A. Sawicki

ABSTRACT: Possible links between certain aspects of pre-failure instabilities of sand (instability line) and plastic dilation are studied. The starting point is experimental results obtained from triaxial investigations, which are approximated separately by analytical formulae for initially contractive and dilative sands. The irreversible strains are deduced from the condition that plastic work (dissipation) should be positive. Then, analytical formulae for plastic dilation are derived and presented in graphical form. In the case of initially contractive sand, a possible link between the instability line and maximum of the plastic dilatancy function is demonstrated. This condition is equivalent to the minimum dilation parameter or maximum of Rowe’s function. In the case of initially dilative sand, it is shown that the negative work done by a mean stress on expanding (dilating) soil should not be treated as dissipative because of thermodynamical requirements. Consequently, the plastic dilation function is zero for shearing stress exceeding the instability line.

Strength Anisotropy of a Residual Soil in Singapore

G. Meng and J. Chu

ABSTRACT: The undrained shear strength of soil is one of the most important parameters required for geotechnical design. Depending on the design situations, the undrained shear strength of soil may have to be determined by different tests. In this paper, some testing data on the determination of the undrained shear strength of a residual soil in Singapore are presented. Large blocks of undisturbed residual soil samples were taken from a construction site of the Deep Tunnel Sewerage System Project in Singapore. To study the inherent strength anisotropy, specimens cut in both vertical and horizontal directions were tests. The anisotropy behaviour of intact residual soil was also investigated under different major principal stress directions. The tests conducted included K0 consolidated undrained triaxial compression (CK0UC) and extension (CK0UE) tests, and K0 consolidated undrained direct simple shear (CK0UDSS) tests. Based on the experimental results, the cu/s10¢ versus OCR relationships of each type of tests are established for practical applications. The failure envelopes and friction angles determined from different types of tests are also compared.

Effect of Boundary Conditions on Shear Banding in True Triaxial Tests on Sand

P.V. Lade and Q. Wang

ABSTRACT: Shear banding in true triaxial tests on sand have been studied to determine its effects on failure under three-dimensional conditions. Experiments have been performed on rectangular prismatic specimens with height-to-diameter ratio H/D = 2.47 and on cubical specimens with H/D = 1.0 to determine the influence of slenderness ratio and stiff versus soft boundaries on the results of such tests. The experiments show clear differences between the two types of tests: Shear banding in the tall specimens occurs with a sharp peak, while the short specimens show smoother stress-strain behavior near the peak, and all friction angles from the short specimens are 1-2 degrees higher than those from the tall specimens. The analysis of shear banding indicates that the critical hardening moduli are closer to zero for the short specimens than for the tall specimens. Indications are that experiments should be performed on tall specimens in which the shear banding occurs freely, while the short specimens impede and delay the development of shear bands.

Behavioural Patterns of Fine Sands

V.N. Georgiannou

ABSTRACT: The behavioural patterns of five fine sands are investigated in the Hollow Cylinder and the triaxial apparatus under undrained loading conditions. The paper focuses on distinctive patterns of undrained response of sands, namely an unstable or brittle response associated with strength reduction after a transient peak and a stable response when a continuous increase in strength with loading is observed. The influence of various parameters such as particle shape, grading, addition of fines, consolidation history, stress level and loading conditions on sand behaviour is examined. Particle shape and angularity has much more significant influence on sand’s response pattern than small variations in the grading curves of uniform sands. However, larger variations in the grading curves or the addition of even small contents of fines (<5%) can also alter the behaviour of a sand from stable to brittle. The response of a sand to cyclic loading is related to its response to monotonic loading. Anisotropic consolidation does not appear to alter the mobilized angle at failure and phase transformation during torsional loading.

Simulating Shear Rate-Dependent Undrained Stress-Strain Behaviour of Natural Sedimentary Clay at Kobe Airport

M.-S. Jung and S. Shibuya

ABSTRACT: Effects of strain rate on undrained shear behaviour of seabed Holocene clay at Kobe airport site were examined in a series of triaxial compression and extension tests performed using different rate of axial straining. A comparative compression test in which the strain rate was changed in steps was also carried out. Similar tests were performed in constant-volume direct shear box (DSB) test. It was found that the undrained strength increased with increasing shear rate and increasing consolidation period. Isotach properties seemed a key to govern the undrained shear behaviour. The behaviour can be described such that the stress-strain response as well as the development of excess pore pressures was uniquely related to the axial strain rate, for which softer and more contracting response was examined when the rate of axial strain decreased, and vice versa as the axial strain rate increased. In this paper, a type of Isotach stress-strain response of the clay, together with the development of drained creep strain with time was successfully simulated by newly developed models.

Experimental Investigation on Settling Behavior of Hong Kong Marine Deposits in Settling Column Condition

F. Tong J.H.Yin and G.F. Zhun

ABSTRACT: Due to the high water content and viscous property, the Hong Kong marine deposit (HKMD) frequently poses challenge to geotechnical practice, particularly to the reclamation in Hong Kong. Formation of HKMD typically goes through sedimentation and selfweight consolidation. These behaviours are time-dependent and hard to describe. A series of one-dimensional settling column consolidation tests were conducted on the HKMD. Results reveal that the settling curve and settling rate are significantly affected by the sediment concentration in self-weight consolidation. Soils even exhibit viscosity in self-weight consolidation. After the primary self-weight consolidation, the settling rate is reduced in the “secondary consolidation”. Related parameters from sketches are evaluated for a better interpretation of the consolidation behaviour.

Development of a Hollow Cylinder Torsional Apparatus for Pre-failure Deformation and Large Strains Behaviour of Sand

E. Ibraim, P. Christiaens and M. Pope

ABSTRACT: A hollow cylindrical torsional apparatus (HCTA) recently developed at University of Bristol, UK is presented. The HCTA apparatus is testing granular soils in drained and undrained, in monotonic but also dynamic loading conditions, and it is equipped with a complex strain measurement system based on high resolution non-contact transducers. The experimental developments are designed to allow the study of the pre-failure deformation characteristics and the large strains behaviour, via a continuous test on a single specimen and, thus, analyze the soil stiffness with the evolution of the strain and stress levels. While the experimental developments and apparatus capabilities in large strains have been explored and validated in an earlier study, this paper describes mainly the precision measurement system, including the assessment of its performance with reference to the soil stiffness.

Effect of High Confining Pressure on the Behaviour of Fibre Reinforced Sand

S. Ud-din, A. Marri and D. Wanatowski

ABSTRACT: Several techniques of soil stabilisation and soil reinforcement are available for improving properties of geotechnical materials. However, the addition of fibre into soils has its unique potential. This is because friction between fibres and soil particles increases bonding between the particles. As a result, the stress-strain behaviour and failure characteristics of both cemented and uncemented soils reinforced with fibres can be improved. In this paper, the influence of fibre and cement on the behaviour of sand in a wide range of confining pressures is studied. Drained triaxial compression tests carried out on uncemented and artificially cemented Portaway sand with 0.5% randomly distributed discrete polypropylene fibres are presented. The experimental results show that stress-strain behaviour and strength characteristics of Portaway sand improve with addition of fibres. However, the effect of fibre reinforcement is more significant at lower confining pressures.

At high confining pressures, the contribution of fibres is suppressed and the effect of high confinement becomes dominant.

A Comment on the Ratio of the Maximum and Minimum Dry Density for Sand

E. Imre, S. Fityus, E. Keszeyne and T. Schanz

ABSTRACT: This work reveals an interesting feature of sand behaviour: the ratio of the minimum and the maximum dry density, D, is about constant. This statement is discussed here on the basis of the analysis of two databases: the database of the “Calibration Chamber” sands and the database of the Danube sands. Results show that although the D values are significantly and systematically different for the Calibration Chamber sands and the Danube sands, the coefficients of variation of the D values for each sample population is very small in each case. The difference in the characteristic D values in each case is explained in terms of differences in the experimental methods used and differences in the geological origin of the soils.

W. Mairaing, A. Jotisankasa and S. Soralump

ABSTRACT: This paper is involved with some applications of unsaturated soil mechanics on several problems in Thailand, namely rainfallinduced landslide, dam engineering as well as other volume change problems. In particular, the concept of appropriate technology has been considered in applying unsaturated soil mechanics for these problems. Utilization of the in-house-built miniature tensiometer and relative humidity sensors with conventional standard apparatus has been proposed as an appropriate technology in the country for testing of unsaturated shear strength, volume change as well as other unsaturated hydraulic properties (Soil-Water Characteristic Curve and permeability function). Regarding rainfall-induced landslide, unsaturated soil mechanics has been used in correlating rainfall intensity with slope instability and developing a critical rainfall criteria which has been used in Geographic Information System (GIS) to create dynamic hazard map as well as providing a real-time early warning of landslide based on soil moisture and rain-fall. A case of leakage detection technique as well as volume change analysis for embankment dam are briefly explained. Finally, some aspects of unsaturated soil mechanics education in Thailand is discussed.

Calculation Of Heave Of Deep Pier Foundations

J.D. Nelson, K.C. Chao, D.D. Overton and R.W. Schaut

ABSTRACT: Design of pier and grade beam foundations in highly expansive soils is one of the most important and challenging aspects of geotechnical engineering. Existing design methods consider only uniform soil profiles, and piers with limited length to diameter ratios. These methods are restricted with regard to evaluation of more complex aspects of pier heave. A finite element method of analysis was developed to compute pier movement in expansive soils having variable soil profiles, complex wetting profiles, large length-to-diameter ratios, and complex pier configurations and materials. The model has been named APEX (for Analysis of Piers in EXpansive soils). This paper describes the method of analysis and demonstrates its validity using several case histories. The results of pier design using APEX are compared with those of both conventional rigid pier analyses and elastic pier analyses. A series of simplified design charts developed using APEX are presented to facilitate its use. The results show the versatility of the model with regard to variable soil profiles and wetting zones.

In-Situ And Laboratory Investigations Of Stress-Dependent Permeability Function And SDSWCC From An Unsaturated Soil Slope

C. W. W. Ng and A. K. Leung

ABSTRACT: Permeability function of an unsaturated soil, k(y), where y is suction, is a vital hydrogeological property that governs seepage in various geotechnical problems. Owing to considerably long test duration, direct measurement of k(y) is often avoided if at all possible. Instead, numerous semi-empirical predictive equations have been developed to determine k(y) indirectly. However, effects of drying-wetting history and net normal stress are not generally considered, casting doubts on the validity of some semi-empirical predictive equations. In this paper, stress-dependent k(y) and stress-dependent soil-water characteristic curve (SDSWCC) of a decomposed silty clay are investigated under both field and laboratory conditions. To measure effects of drying and wetting on k(y) directly, an in-situ one-dimensional (1D) permeability test was carried out using the instantaneous profile method on a saprolitic hillslope in Hong Kong. In the laboratory, a new 1D stress-controllable soil column was developed to determine stress-dependent k(y) and SDSWCC on block samples taken from the same hillslope. Effects of drying-wetting cycle(s) and net normal stress on measured stress-dependent k(y)s and SDSWCCs are explored and analysed. By comparing measured and predicted k(y)s, the predictability of some existing semi-empirical equations is evaluated.

Measurements Of Shrinkage Induced Pressure (Sip) In Unsaturated Expansive Clays

A.J. Puppala, T. Wejrungsikul, V. Puljan and T. Manosuthikij

ABSTRACT: Unsaturated expansive soils are located in many regions of the world. Expansive soils can swell more than 100% and shrink more than 50% of its original volume. When these soil movements are totaled, they often result in significant distress to low overburden structures such as pavements and residential buildings. Cracking occurs when the shrinkage or desiccation induced pressure inside the expansive soil matrix exceeds the tensile strength of the same soils. In general, practitioners use soil tests such as linear shrinkage strain and Atterberg limit tests to determine shrinkage strain potentials of soils. However, these tests do not provide shrinkage induced soil pressures generated within the soil. The main objective of this paper is to present a new technique to measure the shrinkage pressure inherently induced inside the matrix of clays. This test termed as Shrinkage Induced Pressure (SIP) is evaluated for providing repeatable and reliable measurements. SIP test results are compared with Indirect Tensile (IDT) strength test results to explain the shrinkage mechanisms in the soils.

KEYWORDS: expansive clay, cracking, curling, shrinkage, shrinkage induced pressure (SIP), indirect tensile (IDT) strength

Unsaturated Soil Mechanics For Slope Stabilization

H. Rahardjo, A. Satyanaga, E. C. Leong

ABSTRACT: Rainfall-induced slope failures commonly occur in the unsaturated zone above groundwater table in many steep residual soil slopes. During a rainy season, desiccated soils with higher permeabilities will increase rain infiltration into slopes causing an increase in pore-water pressures in the zone above the groundwater table. In addition, the groundwater table may rise to result in a further increase in pore-water pressures. As a result, the shear strength of the soil will decrease and factor of safety of the slope can decrease to below a critical value, triggering slope failure. Therefore, it is important to be able to protect unsaturated soil zone within a slope by controlling the
groundwater level and the flux boundary conditions across slope surface as a slope stabilization method. In this paper, the mechanisms for maintaining unsaturated zone in a slope using several slope stabilization methods are described using field examples involving site investigation, numerical analyses and instrumentation. The effectiveness of each slope stabilization method is assessed using principles of unsaturated soil mechanics.

The Development Of Unsaturated Soil Mechanics At Imperial College, London

J.R. Standing

ABSTRACT: Saturated soil mechanics is a complex subject because of the particulate form of the solid phase of soil, its interaction with the aqueous water phase and also because soil is a product of nature and so has potentially great variability. When the soil dries such that there is also an air phase it becomes unsaturated and its behaviour is far more complex because of the interface between the air and the water and the volumetric response of the air under changing conditions of pressure and temperature. Additionally the pressure in the water phase becomes negative (tensile) and measuring such pressures has until recently been fraught with problems. As many parts of the world are covered by unsaturated soils, understanding their response would significantly enhance engineering design and analysis. This paper describes the research work done at Imperial College over the past decades to advance our understanding of unsaturated soils. The work is considered under four main headings of theoretical formulations, laboratory experimentation, field studies and numerical analysis research.

Climate Change And The Role Of Unsaturated Soil Mechanics

D.G. Toll, J. Mendes, P.N. Hughes, S. Glendinning and D. Gallipoli

ABSTRACT: The Intergovernmental Panel on Climate Change (IPCC) provides convincing evidence of global warming as a result of increased greenhouse gas production. There has been a greater occurrence of extreme climate events in recent decades. We need to ensure that our buildings and infrastructure can cope with such events and possibly more extreme events in the future. A good grounding in unsaturated soil mechanics will be necessary to understand future changes involving the drying and desiccation of soils that will occur in dry seasons and the wetting and infiltration processes that prevail during wet seasons. To predict the impacts of climate change will require the use of robust numerical modelling of climate/soil interactions that can be used to model the effects of future climate regimes. To achieve this we need high quality field observations involving climate/soil interaction that can be used to validate the models. This paper reports on a study in the UK to acquire such data.

Some Mining Applications Of Unsaturated Soil Mechanics

D.J. Williams

ABSTRACT: Unsaturated soil mechanics continues to play poor relation to saturated soil mechanics, although an unsaturated soil at a given density is stronger, less compressible and less permeable (i.e. performs better) than the same soil in a saturated state. There are many examples of unsaturated conditions in the mining field, including the wetting-up and drain-down of initially dry surface waste rock dumps; the irrigation and drain-down of heap leach materials; the drain-down, desiccation and rewetting of mine tailings; the dewatering of mineral products such as coal; the shear strength and compressibility of stored mine wastes; and the performance of geo-covers placed on mine wastes on rehabilitation. This paper highlights the key unsaturated soil mechanics parameters, overviews the nature of mining and processing wastes, and some products, and discusses the issues involved. Some applications of unsaturated soil mechanics addressing the shear strength, compressibility and permeability of mine wastes, and mineral products, are presented, together with data to highlight them.

Tahmeed M. Al-Hussaini, Tahsin R. Hossain and M. Hayeem Al-Noman

ABSTRACT: The Bangladesh National Building Code (BNBC) has not been updated since its inception in 1993. Earthquake design
provisions are important, since Bangladesh is located in a seismically active region not far from the boundary of the Indian Plate and Eurasian Plate. Many advances in earthquake engineering research have taken place over the last two decades. In 2010, a project has been taken up for upgradation of the building code to incorporate current knowledge and developments. Significant changes have been proposed in the seismic design provisions of the updated version of the building code. This paper describes the salient features of the proposed changes to geotechnical earthquake engineering provisions affecting computation of the seismic loads. Major changes have taken place with regard to the seismic zoning map, soil classification system, site-dependent response spectrum, and in defining seismic design category.

Analysis of Soil Liquefaction during the Recent Canterbury (New Zealand) Earthquakes

RP Orense, MJ Pender and LM Wotherspoon

ABSTRACT: Four successive large-scale earthquakes, with moment magnitudes (M w) ranging from 5.9 to 7.1, struck the Canterbury region on the South Island of New Zealand within a period of 15 months in 2010-2011. These earthquakes caused extensive damage to lifelines and residential houses in Christchurch City and adjacent areas due to widespread liquefaction and re-liquefaction in areas close to major streams, rivers and wetlands. In this paper, various analyses were made considering the results of the reconnaissance work conducted immediately after the events, the acceleration records at strong motion sites and the available boring information. The liquefaction risk in the city was evaluated to explain the severity and extent of damage during the 2010 and 2011 events. Finally, simulation of recorded ground motions through 1D effective stress ground response analysis gave a better understanding of the dynamic properties of Christchurch soils.

Numerical Simulation of Seismic Slope Stability Analysis based on Tension-Shear Failure Mechanism

Yingbin Zhang, Guangqi Chen, Jian Wu, Lu Zheng, Xiaoying Zhuang

ABSTRACT: Most slope stability analysis approaches regard the failure mechanism of seismic slope as single shear failure while ignoring the influence of tension failure. However, many model testes and a large number of post-earthquake investigations provided supporting evidence of the significant influence of tension failure in seismic slope instability. To estimate the effects of tension failure on seismic slope stability, a numerical modeling considering both shear and tension failure is performed using FLAC3D. After discussions of failure mechanism, strength reduction techniques and the definition of slope failure, a homogeneity slope under a modified transverse earthquake load is analyzed. The results obtained from the simulation are presented in terms of permanent displacement, factor of safety and failure surface. Finally, the outcomes compared with those from various existing methods. The results show that the influence of tension failure is significant and consideration of it is necessary.
KEYWORDS: Seismic slope stability analysis, Numerical simulation, Failure mechanism, Tension failure, Factor of safety

A Real-time Prediction Method for Regional Rainfall-induced Geohazards in Post-earthquake Region of Wenchuan Earthquake

Z. Yang, J. Qiao, H. Tian, D. Huang, M. Wang and H. Meng

ABSTRACT: After years of the Wenchuan earthquake took place in 12 May, 2008, rainfall has been the most major triggering factor of geohazards in the earthquake stricken areas. As a random event, geohazards including landslides and debris flows occurrence are affected by environmental factors and triggering factors, as a result the hazard degree should be a variational value varying from the regional random precipitation triggering factor and regional geohazards susceptibility assessment environmental factors. According to geohazards mechanism, the probability based method of assessing the variational hazard degree of regional geohazards is proposed by the combination of probability of daily precipitation and susceptibility assessment. The prediction model is established by the analysis of geology and hydrology factors of the study area, which is incorporating with the analysis of geohazards occurrence data and the corresponding precipitation data. Then, the method is applied in earthquake region of Chengdu City, 8 km away from the epicenter of Wenchuan earthquake, Sichuan province. The validity of the prediction method is verified by evaluating the hazard degree of regional geohazards in Chengdu city on September, 24, 2008 and July, 17, 2009. It is found that the occurrence location and occurrence time of the two geohazards from prediction coincide with those from measurement. As a result, this variational hazard degree assessment model for regional geohazards demonstrates a useful application of a new predictive method and provides a basis for the prediction of time and space of regional Rainfall-induced geohazards.

Effects of Anisotropic Consolidation and Stress Reversal on the Liquefaction Resistance of Sands and Silty Sands

Abbas Galandarzadeh and Alireza Ahmadi

ABSTRACT: In this study, a total number of 83 undrained cyclic tests were carried out on Firoozkuh pure sand and sand-silt mixtures using cyclic triaxial apparatus. The tested specimens were subjected to both isotropic and anisotropic consolidation. The anisotropic consolidation was applied both in compression and in extension modes. The results indicate that the isotropic consolidated pure sandy samples when subjected to symmetric cyclic stresses exhibit asymmetric cyclic strains reversely, as extensional part of each cyclic strain curve is larger than compressional part. This behavior of sandy soils could be addressed to the anisotropic behavior of sands. The effect of adding silt on this deformational behavior of sandy specimens is studied too. The results indicated that this behavior disappears in silt mixed sand.

In addition, the effect of anisotropic consolidation on deformational behavior of pure sand and sand-silt mixtures was considered. The results indicate that the cyclic resistance of saturated sand to liquefaction is the function of compressional or extensional consolidation and besides, reversal of cyclic deviator stress. Anisotropic consolidation exerts an initial static deviator stress in triaxial tests. Effect of initial static shear stress on the cyclic liquefaction of sands is acknowledged in the literature and a correction factor of k is introduced to take this into account. However, shear stress reversal in the cases with presence of initial static shear stress is another factor that affects the liquefaction potential. A new coefficient called rc is introduced in this study to show degree of cyclic stress reversal. Combined effect of initial static shear stress and shear stress reversal is studied and it is shown that the correction factor for initial static shear stress k is not sufficient and stress reversal effect should also be considered for correction of cyclic resistance to liquefaction. Effect of initial shear stress and cyclic stress reversal on the silt mixed sands is also studied.

Characteristics of Slope Failures During Natural Disasters Considering Geographical Features and Groundwater Level: Case Study of the Chuetsu Region of Niigata, Japan

H. Toyota

ABSTRACT: Several natural disasters—earthquakes, heavy rainfall, and snow—struck the Chuetsu region of Niigata during the short period of 2004-2011. Recently it has been pointed out that damage by a certain natural disaster is exacerbated by other natural disasters occurring before and after the natural disaster. This phenomenon, designated as a compound disaster, is of widely acknowledged importance. Records of such uncommon disaster circumstances and effects are presumed to be valuable from the viewpoint of disaster prevention. Therefore, actual conditions of damaged areas were investigated in the Chuetsu area to assess the degree of damage, with consideration of geographical features including geology and groundwater level. Moreover, the results of follow-up monitoring related to the damaged slopes during the unprecedented Chuetsu Earthquake are briefly introduced in this paper.
KEYWORDS: ground water level, model test, monitoring on site, site investigation, slope stability

Overview of the Geotechnical Damages and the Technical Problems Posed after the 2011 off the Pacific Coast of Tohoku Earthquake

M. Kazama, T. Noda, T. Mori and J. Kim

ABSTRACT: The 2011 Off the Pacific Coast of Tohoku Earthquake which occurred on March 11, caused serious damage to the infrastructural facilities in Tohoku and Kanto districts due to the strong motion of the earthquake and the subsequent tsunami. This paper includes a brief outline of the earthquake, the earthquake damage to various facilities, and the main geotechnical engineering problems which have emerged after this disaster.

Development of Potentail Map for Landslides Induced by the Chi-Chi Earthquake Using Instability Index

Meei-Ling Lin and Yu-Hung Shu

ABSTRACT: In Taiwan, sloping lands cover more than 70% of the total area, and the geological condition of Taiwan is fairly fragile. The topography, geology, and tectonic setting make it highly prone to landslides induced by earthquake. In this research, data of the landslides triggered by the Chi-Chi Earthquake was analyzed for assessment of the potential and a predictive model was established for landslide occurrence of the area if similar earthquakes occur. Influence factors were selected and the instability index was used for assessing landslide potential. Through verification of an independent set of ground-based investigation data, results of the prediction model appeared to be satisfactory and can be used for mapping of landslide potential induced by similar earthquake in the future.

Geotechnical Hazards with Emphasis on Seismically-Combined Effects on Slopes

Ikuo Towhata

ABSTRACT: This paper first addresses several examples of complex or compound natural disasters with an emphasis of slope instabilities. In many of them, the first effect was produced by earthquakes and the second one was made by heavy rains. Weathering is another kind of the first event. Because the complex events are of stronger action, it is made more difficult to achieve safety. Hence discussion is often made of the importance of relocation of habitats to safer places and/or emergency evacuation. Technical visits to sites of such “soft” measures revealed that the success of those measures depends on education of people and the administrator’s reasonable respect of the people’s need for good jobs and reliable income.

Monitoring on Earthquake Induced Landslide – A Case Study in Northwest Chengdu, China

Hongling Tian, Jianping Qiao., Taro Uchimura and Lin Wang

ABSTRACT: Many after-shock slopes covered by loose deposits, when heavy rain comes, the slope easily slides and turns into debris flow. Thus, the slope movement and the moisture of slope are most important factors for landslide and debris flow. For these style landslides, real-time monitoring is a good way for local people. After analysed the system requirements, the authors proposed an easy-to-use and low power consumption monitoring system. This system consists of two parts, field part and data processing part. The field part includes a few sensors and a data transferring unit. The sensors are made up of tilt sensor, soil moisture meter and rain gauge. A demo system was setup on a sliding slope in Taziping, northwest of Chengdu city. After a field test with artificial rainfall, a criterion for warning was drawn. The demo system has proved it’s effective. It is an economy and simple solution for similar area.

N. Dixon, K. Zamara, D.R.V. Jones, G. Fowmes

ABSTRACT: Despite the relative maturity of landfill design practice, world-wide there are still significant numbers of large scale failures of waste bodies, often incorporating the lining system. In addition, there is growing evidence that post waste placement deformations in the lining system are leading to loss of function (i.e. discontinuous drainage layers, loss on protection and leaking liners). Best practice has established that both stability and integrity of the lining system must be assessed during the design process, and specifically that interaction between the waste body and lining system should be considered both in the short-term (i.e. during construction) and long-term (i.e. following waste degradation). The paper introduces available analysis approaches, reviews knowledge of waste behaviour required for such analyses and provides guidance on the mechanisms to consider. The need for field monitoring to validate numerical models is established as is the need for extensive measurements of waste mechanics properties linked to a standard classification system to aid comparison and use. The benefits of using probability of failure analysis to incorporate material and test variability in design are highlighted.

Wrinkling of a Geomembrane on a Compacted Clay Liner on a Slope

R. K. Rowe, P. Yang, M.J. Chappel, R.W.I. Brachman , W.A. Take

ABSTRACT: The development of wrinkles in a 1.5 mm thick textured HDPE geomembraneover a compacted clay liner on a 3H:1V (33%; 18°) slope is reported at different times of the day on 25 August 2008. The width of wrinkles did not vary significantly throughout the day once notable wrinkling had developed. The mean wrinkle width (0.31 m) is greater than that at other sites with a GCL below the geomembranereported in the literature (0.21-0.23m). The maximum connected wrinkle ranged from less than 20 m at 08:40 to 1370 m at 15:10. Given the size of the area monitored(0.26 ha) one might expect about four such wrinkles per hectare. Wrinkles covered less than 2% of the area at 08:40 but exceeded 8% after 10:10 with a maximum of 20% at 15:10. The practical implications of the time of day the geomembrane is covered and the effect this could have on leakage are discussed.
KEYWORDS: geomembranes, wrinkles, landfills, liners, leakage

Diffusion of phenolic compounds through an HDPE geomembrane

N. Touze-Foltz, M. Ahari, M. Mendes, C. Barral, M. Gardoni and L. Mazeas

ABSTRACT: The experimental results obtained regarding diffusion through a high density polyethylene geomembrane of phenol, o-cresol, p-cresol, 2,4-xylenol, 3,4-xylenol, 2-chlorophenol, 4-chlorophenol, 2,4-dichlorophenol, 2,4,6-trichlorophenol, 2,3,4,6-tetrachlorophenol, 2,3,5,6-tetrachlorophenol, pentachlorophenol and bisphenol A are presented. Partitioning coefficients range from 0.3 to 205 respectively for phenol and pentachlorophenol. Diffusion coefficients lie in the range 1.1×10 -13 to 4.3×10 -13 m 2 /s respectively for 2-methylphenol and bisphenol A. The effect of aqueous solubility, n-octanol/water partitioning coefficient, molecular diameter and molecular weight on partitioning coefficient, diffusion coefficient and permeation coefficient were studied. Different trends from the ones previously given in the literature for volatile organic compounds (VOCs) were observed. An increase in the number of chlorine atom on the phenolic nucleus results in an increase of the partitioning coefficient and permeation coefficient, probably linked to the polarity of the molecules under study.

Shear-Induced Geomembrane Damage due to Gravel in Underlying Compacted Clay

P. J. Fox, C. Athanassopoulos, S. S. Thielmann, and A. N. Stern

ABSTRACT: Lining systems for landfills and heap leach pads are often constructed with compacted clay liners (CCLs) containing significant amounts of gravel. Geomembranes placed against gravelly CCLs are vulnerable to damage due tohighoverburden stress andinterface shear displacement. This invited paper reports results from the first experimental investigation of shear-induced damage to geomembranes placed in contact with gravelly compacted clay. A series of large-scale direct shear tests was conducted for the interface between smoothHDPE geomembranes and CCLs with 20 percent gravel. The tests were performed for normal stress levels ranging from 72 to 1658 kPa to simulate overburden stresses associated with bottom liner systems. Replicate interface shear tests were also performed for normal stresses up to 4145 kPa with a geosynthetic clay liner (GCL) placed in between the geomembrane and the CCL to evaluate protection provided by the GCL. Results indicate that shear displacement between a geomembrane and a gravelly CCL under high normal stress conditions can cause severe damage to the geomembrane. The testing program also found that placing a GCL between a geomembrane and a gravellyCCL can essentially eliminate such damage.

Evaluation of mineral barriers against acid rock drainage

A. Naka, T. Katsumi, G. Flores, T. Inui, T. Ohta, T. Urakoshi, and T. Ishihara

ABSTRACT: The barrier performance of geosynthetic clay liners (GCLs) containing Na-bentonite, zeolite, and ferrihydrate against acid rock drainage (ARD) was evaluated through hydraulic conductivity and sorption tests in order to determine their applicability as adsorption layers in waste rock containment facilities. The hydraulic conductivity (k) of GCL permeated with water was 1.4×10-11 m/s and this increased by one order of magnitude with ARDpermeation (k= 5.0×10-10 m/s). The k of zeolite permeated with water was 3.0×10-10 m/s and this also increased with ARDpermeation (k = 1.4×10-9 m/s). The k value of ferrihydrate was 7.3×10-9 m/s when permeated with water and this remained constant after ARD permeation (k= 8.6×10-9 m/s). Metal sorption of bentonite, zeolite, and ferrihydrate were different in terms of sorption capacity and selectivity, which can be summarized as follows: bentonite: Cu>Fe>Zn>Al>As>Pb, zeolite: Cu>Fe>Zn>Pb Al As, and ferrihydrate: Cu>Zn>Al>As>Pb. According to experimental results, the tree minerals appear to be good candidates for ARD mitigation.

Improvement on the Performance of Geosynthetic Clay Liners Using Polymer Modified Bentonite

Y. Liu, W. P. Gates and A. Bouazza

ABSTRACT: Polymers have been added to improve bentonite swelling capacity with the view of improving the hydraulic performance of GCLs. This paper presents an on-going study in which three bentonites were polymer-treated (0.5%, 1%, 2% by weight) and polymerincluded changes to swell index and Atterberg limits were determined. The liquid limit values generally increased with polymer content, although a decrease appeared at higher concentration of some polymers. However, polymer addition had only slight effects on plastic limits. Higher polymer concentration, regardless of type, generally resulted in higher swell index values and swell percentages. Different response of bentonites to polymers occurred which is mainly due to the individual characteristics of bentonites, such as chemical composition, type of gel formation etc.

Effect of Settlement rate and Geogrid reinforcement on the Deformation Behaviour of Soil barriers of Landfill Covers: Centrifuge Study

S. Rajesh and B.V.S. Viswanadham

ABSTRACT: The objective of this paper is to examine the influence of settlement rate and geogrid reinforcement on the deformation behaviour of soil barriers of landfill covers subjected to differential settlements. A series of centrifuge tests were performed on soil barriers at 40 gravities. Two different settlement rates were induced using motor-based differential settlement simulator designed for a high gravity environment. Centrifuge tests on a 1.2 m thick unreinforced soil barrier subjected to two different settlement rates without provision of any overburden pressure was found to experience identical deformation profiles and cracking pattern. A slight delay in the occurrence of crack initiation and an increase in the strain at crack initiation was noticed when the soil barrier was tested at slow settlement rate. An increase in the limiting distortion level from 0.044 to 0.069 was noticed when the unreinforced soil barrier was subjected to an overburden pressure equivalent to that of cover system. When the soil barrier was reinforced with a geogrid layer without any overburden pressure, the limiting distortion level was increased from 0.044 to 0.064. An increase in the maximum mobilized tensile load of model geogrid from 77 kN/m to 120 kN/m was observed with the provision of overburden pressureequivalent to that of cover system.

Effect of differential settlements on the sealing efficiency of GCLs compared to CCLs: Centrifuge Study

B.V.S. Viswanadham, S. Rajesh and A. Bouazza

ABSTRACT: Geosynthetic clay liners (GCLs) are being used as an alternative to compacted clays in landfill cover systems because of their very low hydraulic conductivity to water and ease of placement. The main objective of this paper is to examine the performance of GCLs subjected to continuous differential settlements during a centrifuge test at 40 gravities. This paper presents results to two centrifuge model tests, one on clay-based cover system and another on GCL-based cover system. Both models were subjected to an overburden equivalent to that of landfill covers and are instrumented to measure sealing efficiency at the onset of differential settlements. Limiting maximum distortion level at which the barrier system loses it sealing efficiency could be established. For the type of cover systems investigated, the ability of GCL-based cover system to withstand differential settlements without losing their sealing efficiency was found to be superior to that of clay based cover system.

Geosynthetic Lining System for Modern Waste Facilities – Experiences in Developing Asia

H. B. Ng and B. Ramsey

ABSTRACT: The applications of geosynthetic liner systems are being used with increasing frequency, particularly for the environmental engineering applications in developing countries at recent years. Polyethylene geomembrane sheets have been widely accepted as a standard component of geosynthetic lining system in the waste containments for decades, which includes solid waste sanitary landfill and wastewater treatment lagoons. The paper presents the application of impervious Polyethylene geomembrane used as bottom liners and final capping systems in waste containment facilities in developing Asia. This paper discusses the characteristics and durability of polyethylene geomembrane as a lining solution to the waste containments. Successful case histories on the application of polyethylene geomembranes in bottom liner and final capping systems of modern solid waste facilities are illustrated.

A. S. Bradshaw, A. C. Morales-Velez and C.D.P. Baxter

ABSTRACT: This paper evaluates the applicability of existing Cone Penetration Test (CPT) soil type and soil properties correlations in two different deposits of uniformly graded non-plastic silt. Current CPT correlations for soil engineering properties are based largely on experience in either sands that are typically drained during penetration, or clays that are typically undrained. Silts may exhibit partially drained conditions during penetration that introduces uncertainty when applying correlations from the literature. The assessment is based on an analysis of existing CPT data collected at two study sites in Rhode Island, U.S.A. that are underlain by thick deposits of non-plastic silt. Existing CPT correlations were used to predict the soil type and selected geotechnical properties of the silt, which were compared to laboratory test results to evaluate the quality of the predictions. The silts in this study exhibited partially drained to drained behaviour during cone penetration. Existing CPT soil classification charts were ineffective in identifying the silt but correctly characterized its engineering behaviours. Existing CPT correlations accurately predicted the friction angle, shear wave velocity, and cyclic resistance of the silts investigated in this study.

Characterisation of quick clay at Dragvoll, Trondheim, Norway

A. Emdal, M. Long, A. Bihs, A. Gylland and N. Boylan

ABSTRACT: A detailed characterisation of the quick clay underlying the NTNU research site at Dragvoll, Trondheim is presented. The objective of the work is to provide guidance on quick clay parameters to engineers and researchers working with similar clays in Scandinavia and North America. Dragvoll clay is characterised by its high sensitivity and is quick at relatively shallow depth. The material exhibits low undrained shear strength and high compressibility except over a shallow overconsolidated zone. Its properties are similar to other quick clays in the area and are consistent with well know correlations for Norwegian clays. A combination of simple index tests such as water content and Atterberg limits and CPTU testing proved very useful in characterising the material. The material is very sensitive to sampling and laboratory handling. Results of standard and non standard tests, such as piezoball testing, are presented.

Field response of push-in earth pressure cells for instrumentation and site characterization of soils

Alan J. Lutenegger

ABSTRACT: The use of Push-In Earth Pressure Cells in Geotechnical Engineering is described. Applications for both instrumentation and site characterization are discussed. Several examples of the field response of Push-In Earth Pressure Cells in soils are shown to illustrate their behaviour. These instruments can provide a reasonably simple, economical and reliable tool for a wide range of applications in geoconstruction and site characterization and should be considered by engineers more frequently. A discussion of the interrelationships between the Initial Lateral Stress Ratio and the Reconsolidation Lateral Stress Ratio suggests that in fine-grained soils these values should be related to the stress history of the soil through the overconsolidation ratio.

Frequent-interval SDMT and continuous SCPTu for detailed shear wave velocity profiling in soils

T. Ku and P.W. Mayne

ABSTRACT: Two new approaches to downhole shear wave velocity (Vs) measurements are presented, including frequent-interval method by seismic flat dilatometer (FiSDMT) and continuous-interval method by seismic piezocone testing (CiSCPTu). A recently-awarded patent for a roto-autoseis source assists in both methods by generation of fast and repeatable wavelets that are recorded by the probes during advancement. In the case of frequent-interval SDMT, either pseudo-interval or true-interval Vs data are procured at the same depth intervals of 0.2-m as the normal lift-off pressure (p0) and expansion pressure (p1) and therefore is a slowest version of downhole testing. This offers the advantage of accurate and detailed small-strain stiffness measurements (i.e., Gmax) that can be useful in careful settlement calculations, pavement subgrade designs, and paleoliquefaction studies with shallow fine resolution requirements. In the continuous SCPTu, the autoseis generates wavelets as frequently as every 1 or 2 seconds, thus a fastest type of downhole testing. As there are considerable issues with signals that are complex because of refraction effects, variable penetration rates, noise, and vibration, special measures in processing are required in order to extract the Vs profile. The result offers continuous profiles of qt, fs, u2, and Vs with depth from a single sounding.

KEYWORDS: cone penetration, dilatometer, geophysics, in-situ testing, shear wave velocity, seismic flat dilatometer, seismic piezocone

In situ testing of peat – a review and update on recent developments

M. Long and N. Boylan

ABSTRACT: This paper reviews the techniques used and some recent developments on in situ testing of peat for the purposes of the design and surveillance of engineering structures. Geophysical techniques, especially ground penetrating radar, are now being used extensively in peatlands. All geotechnical in-situ tests in peat can be influenced by partial drainage and therefore can give misleading results if not used carefully to well established guidelines and if not interpreted correctly. There is therefore a benefit in multi-measurement tests (e.g. CPTU and piezoball) which give additional information to help assess the drainage condition. There seems promise in the use of the pore pressure measurements for both CPTU and piezoball for the purposes of profiling peat decomposition and possibly shear strength assessment. Field vane testing will frequently give misleading results. Other standard geotechnical techniques may only be useful when used in conjunction with locally derived empirical correlations. Pore pressure measurements in peat may be influenced by the presence of gas in the deposits.

Understanding the stiffness of soils in Singapore from pressuremeter testing

K.H. Goh, K. Jeyatharan and D. Wen

ABSTRACT: The stiffness of soil is an important parameter that affects the prediction of ground deformation and impact on adjacent structures due to construction activities such as deep excavations and tunnelling. Whilst constitutive models and analytical methods have been derived to predict soil deformation from its stiffness, engineers face a difficult task of identifying soil stiffness from routine site investigations. This paper discusses the use of pressuremeter testing in site investigations to estimate the soil modulus for design.

In recent years, an intensive regime of pressuremeter testing was implemented along with conventional soil investigation works for the land transportation infrastructure construction in Singapore. These include the investigations in the Downtown Line project on Kallang Formation and the Old Alluvium soils, investigations in the North-South Expressway and Thomson Line projects on the Bukit Timah Granite Formation, and investigations in the Tuas West Extension project on the Jurong Formation. This paper reports on the use of various types of pressuremeter testing in Singapore – namely the Menard pressuremeter, the OYO pressuremeter and the self-boring pressuremeter – in terms of the practical experience and the interpretation of pressuremeter test results to understand the stiffness of local soils.

The paper begins by summarising the applications and limitations for various types of pressuremeters in in-situ testing, before discussing the lessons learned from using these pressuremeters in Singapore. Some of the improvements include relating the pressuremeter modulus to the corresponding strains from which they are derived, as well as developing guidance for operators on when to start the unloading cycle. Empirical relationships using SPT-N correlations would also be recommended based on the pressuremeter tests for the various local soils. Other than its elastic modulus, the small strain stiffness of soil has also been investigated to various extents depending on the type of pressuremeter test. These in-situ investigations will improve on the understanding of soil stiffness in Singapore.

Rate effect on cone penetration test in sand

F. A. B. Danziger and T. Lunne

ABSTRACT: A literature survey has provided quite variable results with respect to rate effect on cone penetration test(CPT) in sand. Most of the available data refer to the penetration rate in the range 2 mm/s – 20 mm/s, and show some rate effect. The analysis of the data shows that the factors controlling rate effect on CPT in sand are excess pore pressure generation (in the case of loose silty sands and loose fine sands) and grain crushing (especially in the case of dense sands). Excess pore pressure generation produces a reduction in cone resistance when the rate is increased from 2 mm/s to 20 mm/s, while the opposite occurs in the case of grain crushing. Since the stress level influences grain crushing, the higher the stress level the higher the rate effect. Moreover, the higher the crushability of the sand grains, the higher the rate effect. There is scarcity of tests at high rates. Few data available from tests with variable high rates indicate a significant rate effect.

In situ measurement of hydraulic conductivity of saturated soils

D.J. DeGroot, D.W. Ostendorf and A.I. Judge

ABSTRACT: The hydraulic conductivity of saturated soilsvaries significantly from approximately 10-13 m/s for high plasticity clays to 1 m/s for clean, uniformly graded, coarse gravels. This very large range in possible values has resulted in the developed of numerous fieldmethods that cater to the soil type being tested and the anticipated hydraulic conductivity. The most common in situ method used in practice is the slug test as performed in open standpipe piezometers. Other methods include in situ dissipation tests and large scale pumping tests. This paper describes these various in situ measurement and analysis options and presents results obtained for a variety of soils including clays, silts, sands and gravels. The examples highlight the major influence of soil type on measured hydraulic conductivity values and also show the secondary influence of soil fabric and scale effects.

KEYWORDS: hydraulic conductivity, in situ testing, slug tests, dissipation testing, pump tests

Ahmed B Mabrouk and R Kerry Rowe

ABSTRACT: A study of excavations within normally to slightly over consolidated deposits over a gas source is presented with reference to the potential for gas venting from a bedrock aquifer. The effects of key design factors on excavation integrity and potential of inducing hydrofractures are examined. Based on the calculated gas distribution, the study introduces the gassy effect to the deepest 6 m of the clayey layer by: a) increasing pore fluid compressibility, b) reducing Young’s modulus of soil skeleton. The study illustrates the importance of considering hydrofracturing potential and gassy behaviour when assessing the stability of excavations in deposits overlying a gas source.

Effects of Consolidation and Specimen Disturbance on Strengths of Taipei Clays

Richard N Hwang, Za-Chieh Moh and I-Chou Hu

ABSTRACT: Presented herein are the results of a study supplementing the one carried out in the early 90’s for investigating the characteristics of Taipei clays for the design and construction of the Taipei Metro. It has been found that the lowering of piezometric level in the Chingmei Formation in the 70’s has drastically increased the shear strengths of the clays which can be estimated by using the SHANSEP equations, as a result of consolidation. Furthermore, the shear strengths obtained in the routine unconsolidated undrained shearing tests are far too low due to specimen disturbance.

Lime Stabilisation of Organic Clay and the Effects of Humic Acid Content

NZ Mohd Yunus, D Wanatowski and LR Stace

ABSTRACT: The effectiveness of lime as a chemical additive for the stabilisation of organic clay is considered uncertain, especially in the long term. The presence of humic acid is believed to be the main detrimental constituent of organic matter that renders lime stabilisation inefficient. In this paper, the amount of humic acid that may render lime stabilisation inefficient was carefully investigated. Artificial organic clay, prepared by mixing commercial kaolin and various amounts of humic acid (0.5%, 1.5% and 3.0%) was treated with hydrated lime. The strength properties of lime-treated organic clays were examined by unconfined compressive strength (UCS) and drained and undrained triaxial compression tests. Curing periods of 7, 28 and 90 days were chosen as key points to monitor the evolution and the effect of the stabilisation process on lime-treated specimens. Overall, the development of physical and engineering properties of lime-treated organic clay was most affected when the humic acid content in clay exceeded 1.5%.

Estimating Wetting-induced Settlement of Compacted Soils using Oedometer Test

EC Leong, S Widiastuti and H Rahardjo

ABSTRACT: Compacted soils undergo volume changes when wetted. Oedometer tests have been commonly used to estimate the settlement of unsaturated soils when wetted. Several variations of the oedometer test are available. The double-oedometer test has been more popular as it requires only two nominally identical specimens for the test to produce the unsaturated and saturated compression curves. The wetting induced settlement of a compacted soil at any load can be estimated by the difference in ordinate between the unsaturated and saturated compression curves. In this paper, it is shown that the unsaturated and saturated compression curves are linked by the initial degree of saturation and soil type. The compression curve of an unsaturated compacted soil can be derived from the compression curve of an inundated compacted soil, making it possible to estimate the wetting-induced settlement of compacted soils using a single oedometer test on an inundated specimen.

Compaction Curve with Consideration of Time and Temperature Effects for Mudstones

A Puttiwongrak, H Honda, T Matsuoka and Y Yamada

ABSTRACT: A compilation of compaction curves shows that the curves vary widely (porosity-burial depth), especially at the depth shallower 2000 m. There is no unique physical or mathematic expression of mudstone compaction. In this study, we have considered the burial depths (shallower 2000m), where the process of mechanical compaction dominate, and point out on time and temperature effects influencing variations of mudstone compaction curves. We revised and reconstructed the existing, widely referred, mudstone compaction curves using a correction of clay mineral dehydration and thermal correction based on time and temperature effects, respectively. The results show that the mudstone compaction curves seem to improve matching with one another. These corrections are possible toward establishment of a standard compaction curve of mudstones.

Small strain behavior of sand under various stress paths considering anisotropic initial stress state

Lai Yong, Shi Jian-yong, Yu Xiao-jun and Cao Qiu-rong

ABSTRACT: The stress-strain characteristics in small strain region for a Chinese sand were investigated under different stress paths. The strain contour circle method was used to simulate the small strain characteristics of the sand under various stress paths. The test results showed that the inherent stress-strain characteristics of the sand depend on the anisotropic initial stress state. The contraction and dilation behaviors of the tested sand under various K₀ initial stress conditions are different from that under isotropic initial stress state conditions. The test results of the sand agreed with the Wong-Mitchell’s research results very well. The strain contour circle method can approximately simulate small stress-strain characteristics of the sand for various stress paths by using the proportion function λ and expansion function l. The calculation results from the new method agree with the test results for Bothkennar clay.

Study of Joint Effect on Pipe in Pipe Jacking Method

L G Le, M Takise, M Sugimoto and K Nakamura

ABSTRACT: Recently, pipe jacking method has become popular in micro tunnelling because of its benefits for economy and environment. However, jacked pipes have complex performance during installation process, particularly when the pipes are driven through a curved alignment. In such a case, the joints between the pipes significantly affect the behaviour of the pipes and the alignment deviation. To investigate the influence of joints on pipes, full scale tests and numerical modelling were carried out to simulate pipe jacking of two consecutive pipes in both straight and curved alignments. It was found that stress concentration occurs along pipe length at the range where cushion materials are set for both alignments and at the concave side of curve for the curved alignment. In addition, it was confirmed that the stack pipe model gives a reasonable result to simulate the experiments for the pipe jacking method.

Finite Element Analysis of Ground Behaviour due to Box-jacking Tunnel Work

K Komiya and T Nakayama

ABSTRACT: A box-jacking tunnel method is a new mechanized tunnelling method which has been developed to construct large scale tunnels undercrossing the existing traffics in urban areas. During the box jacking operation, a box-module is driven forward by applying mechanical forces and excavating the soil in front of the box-module with boring machine. The step-by-step insertion of the box-module forms a lining frame of the tunnel in the ground and after completion of the lining frame, the tunnel is complete by excavation of soil within the internal section of the frame. In this study, the step-by-step advancement and excavation processes of the box-module are modelled using the finite element method with the finite element remeshing technique. Three dimensional finite element analyses are conducted to simulate the construction process of a box jacking tunnelling work and the numerical results are compared with the field measurements.

Tunneling Induced Deformation of a Historic Building in Shanghai

Shi-ping Gea, Dong-wu Xied, Wen-qi Dinga, Ya-fei Qiao and Jin-chun Chai

ABSTRACT: Tunnelling induced deformations of a historic building, Chongsi Building, in Shanghai, China, are reported. The construction site located in Xuhui District, along the Metro line 11, and at the site the thickness of soft soil layer, soft clay and clayey silt, is about 30 m. The tunnelling method used is the earth pressure balance (EPB) shield tunnelling. The building with masonry structure was built about a century ago, and there were already considerable deformations. Considering this situation, the criteria for total and incremental deformations have been proposed; especially the twist criteria have been newly established and applied to the project. Controlling both the total and incremental deformations is called Dual-control criteria (DCC). The measured maximum settlement, differential settlement, and twist during tunnelling construction were 13.29 mm, 0.67 mm/m, and 3.23×10^-5 rad/m respectively. Based on the monitoring results, the deformations of the historic building during and after tunnel construction were very small and, causing no serious damage to the building, and it is considered that the construction control is successful.

KEYWORDS: tunnelling, historic building, underground crossing, deformation criteria

In-situ monitoring of internal displacements by FBG sensors and slope stability analysis under rainfall infiltration

Dongsheng Xu, Fei Tong, Huahu Pei, and Jianhua Yin

ABSTRACT: The Wenchuan earthquake in Sichuan Province of China has caused tremendous loss of life and property. The severe earthquake along with the heavy rainfall has induced landslide and debris flows so that the slope stability is a significant concern in this earthquake region. A newly developed inclinometer based on the Fiber Bragg Grating (FBG) sensing technique has been installed in a slope in Sichuan Province for long-term monitoring of internal displacements. A series of FBG sensing bars are installed at different depths of two different boreholes in the slope; meanwhile, all optical fibers of the sensing bars are connected and extended to a monitoring station around 1000m away from the slope site through a main armored cable of optical fibers. Monitoring works are carried out in the monitoring station from 20 June to 25 September 2010. Thus, internal displacements of the slope are analyzed together with the rainfall data which are also collected by a rainfall gauge. The results demonstrate that rainfall infiltration has a strong influence on the internal displacements, while the influence reduces dramatically when the depth exceeds 5.2m. Through a numerical model for the effect analysis of rainfall intensity and duration, the slope stability decreases significantly when the rainfall intensity higher (or equal) than 0.5mm/h and rainfall duration longer than 100h.

Mechanistic-Empirical Pavement Design: A Brief Overview

A T Papagiannakis

ABSTRACT: This paper provides an overview of the state of the art of mechanistic-empirical pavement design, as established by NCHRP Study 1-37A in the United States. It describes the method used to characterize traffic loading and materials, as well as the methods used to analyse flexible and rigid pavement response and calculate damage. This methodology is referred as the Mechanistic-Empirical Pavement Design Guise (MEPDG) and was recently implemented into the commercially available software referred to as the AASHTOWare Pavement Mechanistic Empirical Design.

K. Fujisawa, A. Murakami, S. Nishimura and T. Shuku

ABSTRACT: Thus far, the focus of studies on seepage failure, known as sand boiling or the piping phenomenon, has been to determine the critical hydraulic gradient or the critical seepage flow velocity. However, the transport of soil after seepage failure also needs to be well investigated in order to estimate the damage to soil structures or the ground. The purpose of this study is to experimentally investigate the relationship between the seepage force and the velocity of the sand particles during sand boiling induced by upward and horizontal seepage flows. In the experiments, silica sand is used as the test material and the migration velocities of the seepage water and the sand particles are calculated from the measured amounts of their discharge. The test results reveal that the equilibrium of the forces exerted on the sand particles, i.e., gravity, buoyancy and fluid-particle interaction, can be successfully used to estimate the velocity of the sand particles subjected to upward seepage flow and that the seepage force needed for the horizontal transport of the sand tends to decrease as the velocity of the sand particles increases.

A density-and stress-dependent elasto-plastic model for sands subjected to monotonic undrained torsional shear loading

G. Chiaro, J. Koseki and L.I. Nalin De Silva

ABSTRACT: A density- and stress-dependent elasto-plastic model for saturated sands undergoing monotonic undrained torsional shear loading is presented in this paper. The model is developed under an extended general hyperbolic equation (GHE) approach, in which the void ratio and stress level dependence upon stress-strain response of sand is incorporated. Most importantly, a state-dependent stress-dilatancy relationship is introduced to account for the effect of density on the stress ratio. Such a stress-dilatancy relation is used for modeling the excess pore water pressure generation in undrained shear conditions as the mirror effect of volumetric change in drained shear conditions. In this paper, details of the model formulation and soil parameters calibration are described. By using the proposed model, numerical simulation of monotonic undrained torsional shear tests have been carried out on Toyoura sand. The model predictions show that undrained shear behavior, described in terms of stress-strain relationship and effective stress path for both loose and dense sands, can be modeled satisfactorily by using a single set of soil parameters.

1-G model test with digital image analysis for seismic behavior of earth dam

Y. Miyanaga, A. Kobayashi and A.Murakami

ABSTRACT: This paper proposes a new experimental method using small 1-G shaking table tests to investigate the seismic behavior of an earth dam. In this research, a digital image analysis was applied to observe strain distributions during excitation. White gauge points were placed on the surface of the model and the movements of these points were analyzed via successive digital image pictures. From the displacements of the gauge points, the distributions of shear strain and volumetric strain were examined as the functions of the acceleration response of the dam body. As a result of the volumetric strain distributions, it was found that vertical tension and compression zones exist in turn, and that tensile stress was observed at the top of the model. It was estimated that the crack at the crest of the earth dam, brought about by the earthquake, was attributed to the tensile stress.

X-ray CT imaging of 3-D bearing capacity mechanism for vertically loaded shallow foundations

D. Takano, J. Otani, M. Nakamura, and R. Mokwa

ABSTRACT: The three-dimensional bearing capacity of shallow foundations has not been fully investigated because of the difficulty in visualizing and understanding the complex three-dimensional failure mechanism. In this paper, a series of model loading tests were conducted on shallow foundations with square and rectangular shaped footings X-ray CT scanning techniques were utilized to nondestructively visualize and investigate the soil behavior during the loading tests. Based on the tomographic results for four different footing geometries, both surface deformations and below ground deformations along the failure surface cross section are described and three-dimensional failure mechanisms illustrated. A gradual change or progression of the bearing capacity failure pattern was observed and quantified as the footing aspect ratio changed from a square foundation to a rectangular shape that approached plane strain conditions. It is anticipated that the process and technique developed in this study could be beneficial in understanding and quantifying the mechanics associated with other soil-structure interaction problems, especially complex problems in which the failure mechanism is difficult or impossible to predict using conventional geotechnical engineering principles.

Modeling and bending test simulations of cement treated soil

K. Kaneda, T. Tanikawa and S. Onimaru

ABSTRACT: Cement treated soil, which is commonly utilized to prevent liquefaction and/or to increase the bearing capacity of soft clay foundations, is characterized by four basic properties: 1) its strength is greater than that of untreated soil, yet less than that of concrete, 2) it exhibits nonlinear behavior close to its peak strength, 3) softening occurs after its peak strength has been exceeded, and 4) the extension strength is found while the soil is not considered. In this study, the subloading surface model introduced by Hashiguchi was incorporated into a modified Drucker-Prager criterion, and undrained triaxial compression tests of cement treated soil were performed under constrained pressures of 0.1 and 0.4 MN/m2, after which bending tests and simulations were performed. The numerical results of these tests agreed well with the actual results of element wise and boundary condition testing.

Modelling viscous effects during and after construction in London Clay

S. D. Clarke and C. C. Hird

ABSTRACT: A new approach to allow the modelling of the viscous behaviour of clay soils has recently been developed (Clarke & Hird, 2012) based on the BRICK constitutive model (Simpson, 1992). In this approach viscous effects, such as creep and stress relaxation, and the effects of strain history on soil stiffness are modelled within a single conceptual framework. The developed model, SRD (strain-rate dependent) BRICK, has been incorporated in a finite element program, allowing boundary value problems to be analysed. In this paper two case histories involving London Clay, where viscous effects possibly had an influence on the observed displacements, are back-analysed. These cases are the Jubilee Line extension at St James’s Park (Standing et al., 1996, Nyren et al., 2001) and a deep basement at Horseferry Road (May, 1975, Chapman, 1999). The results of the numerical modelling show that, in each case, the SRD BRICK model is able to achieve closer agreement with the recorded displacements when compared with the unmodified BRICK model.

Modelling viscous effects during and after construction in London Clay

S. D. Clarke and C. C. Hird

ABSTRACT: A new approach to allow the modelling of the viscous behaviour of clay soils has recently been developed (Clarke & Hird, 2012) based on the BRICK constitutive model (Simpson, 1992). In this approach viscous effects, such as creep and stress relaxation, and the effects of strain history on soil stiffness are modelled within a single conceptual framework. The developed model, SRD (strain-rate dependent) BRICK, has been incorporated in a finite element program, allowing boundary value problems to be analysed. In this paper two case histories involving London Clay, where viscous effects possibly had an influence on the observed displacements, are back-analysed. These cases are the Jubilee Line extension at St James’s Park (Standing et al., 1996, Nyren et al., 2001) and a deep basement at Horseferry Road (May, 1975, Chapman, 1999). The results of the numerical modelling show that, in each case, the SRD BRICK model is able to achieve closer agreement with the recorded displacements when compared with the unmodified BRICK model.

S.Kimoto, F.Oka and E.Garcia

ABSTRACT: Frequent failures of river embankments have occurred in the world due to heavy rains. Heavy rainfalls bring about an increase of the ground water level within the soil as well as a rise in the water level of the rivers. As a result, embankments have been failed due to the rainfall infiltration and the generation of seepage flow. A series of two-dimensional numerical analyses of river embankments are carried out using a seepage-deformation coupled method for unsaturated soil. The mechanism of the surface deformation and the strain localization on these soil structures are discussed mainly with respect to the water permeability of the soils. Results obtained by the simulations show that the deformation of the embankments significantly depends on the water permeability of the soil and it is localized on the slope surface at the river sides. The larger the saturated water permeability of the soil, the larger the velocity of the seepage flow and the larger the deformation on the surface of the river embankments. Additionally, numerical simulations of a field experiment are used to show that, the method adopted here, can effectively be used to study the practical seepage deformation coupled problems on unsaturated soils.

Seismic Response of Gravity-Cantilever Retaining Wall Backfilled with Shredded Tire

N. Ravichandran and E. L. Huggins

ABSTRACT: Using shredded tires as an alternative backfill material for retaining walls is an effective method for recycling a common and abundant waste material. In this paper, the engineering properties of the shredded tire from various sources were compiled; retaining walls were designed for static and seismic conditions using the mean properties following LRFD method and compared with that of conventional granular material. The performance of retaining wall backfilled with shredded tires was then investigated by applying design earthquake acceleration-time histories using advanced finite element software and compared with that of sand backfill. In addition, a detailed parametric study was conducted to quantify the effect of variations in shredded tire properties and earthquake loadings. Results show that the shredded tire backfill significantly reduces the wall tip deflection and maximum shear force and bending moment along the wall. Parametric studies on the shredded tire properties determined that cohesion has the greatest effect on the shear force and wall tip deflection. The friction angle showed the most influence on the bending moment in the wall. Quantitative and qualitative analysis of wall response with variations in shredded tire properties provide guidelines for the design of walls to be backfilled with shredded tires and for the selection of backfill materials.

Numerical modeling of lateral response of long flexible piles in sand

Md. Iftekharuzzaman and Bipul C Hawlader

ABSTRACT: The behavior of a steel pipe pile in sand subjected to lateral load is examined by finite element (FE) analysis. Threedimensional finite element analyses are performed for pure lateral load applied at 0.3m above the ground surface. The FE analyses are performed using the commercially available software package ABAQUS/Standard. The sand around the pile is modeled using a modified form of Mohr-Coulomb soil constitutive model. The modification involves the variation of mobilized angle of internal friction and dilation angle with plastic shear strain. The nonlinear variation of elastic modulus with mean effective stress is also considered in the present FE analyses. These important features of soil constitutive model have been implemented in ABAQUS/Standard using a user subroutine. Numerical analyses are also performed by using the LPILE software, which is based on the p-y curve. The FE and LPILE results are compared with the results of a full-scale test. It is shown that the FE analysis with modified Mohr-Coulomb soil model can successfully simulate better the response of a pile under lateral load. Comparing the numerical results with the full-scale test results some limitations of the p-y curve method are highlighted.

A New Sampling Algorithm in Particle Filter for Geotechnical Analysis

T. Shuku, S. Nishimura, K. Fujisawa and A. Murakami

ABSTRACT: This paper discusses the applicability of the particle filter (PF) algorithms to geotechnical analysis through some numerical tests. Although several types of the PF algorithms have been proposed so far, this study focuses on three typical PF algorithms: sequential importance resampling (SIR), sequential importance sampling (SIS), and merging particle filter (MPF). First, a geotechnical parameter is identified using the three algorithms in both total stress and soil-water coupled analyses, and the effectiveness of each algorithm is investigated. The test results clarify that (1)SIS can be applied to non-Markov dynamics such as elasto-plastic problems, but degeneration problems are often encountered, and (2)MPF can avoid the degeneration problems, but it cannot be applied to non-Markov dynamics. To overcome the dilemma, an algorithm which can treat non-Markov dynamics and solve the degeneration problems is newly proposed. The proposed algorithm is applied to an element test, and the performance is demonstrated experimentally.

Comparison of deep foundation systems using 3D finite element analysis employing different modeling techniques

F. Tschuchnigg & H.F. Schweiger

ABSTRACT: Finite element analyses for the deep foundation of the Donau City Towers in Vienna are discussed in this paper. The towers are located very close to each other, thus interaction of the two towers has to be taken into account for the design of the foundation system. The objective of the analysis was twofold, namely to calculate maximum and differential settlements to be expected and optimisation of the layout of the foundation elements. In addition to the foundation concept actually constructed alternative solutions have been studied in a numerical study and the results of this study are presented in this paper. Different techniques for modelling the foundation elements in the numerical model, namely a standard approach using volume elements and the embedded pile concept, are investigated. The latter approach is discussed is some detail before the case study is presented.

Application of a constitutive model for swelling rock to tunnelling

B. Schadlich, T. Marcher and H.F. Schweiger

ABSTRACT: Swelling due to chemical processes is a well-known problem in tunnelling in anhydritic rocks and certain types of claystone. If the swelling rock mass is exposed to water due to tunnel excavation or natural water influx, in anhydritic rocks large deformations of more than 1 m can be observed, which are typically concentrated at the tunnel invert. Estimating swelling deformations and swelling pressures is of paramount importance for the design of durable underground structures in such materials. This paper presents the results of a numerical back analysis of measured swelling deformations with a simple constitutive model, using swelling parameters derived from laboratory swelling tests.

Finite element modelling of seismic liquefaction in soils

V. Galavi, A. Petalas and R.B.J. Brinkgreve

ABSTRACT: Numerical aspects of seismic liquefaction in soils as implemented in the finite element code, PLAXIS, is described in this paper. After description of finite element equations of dynamic problems, three practical dynamic boundary con ditions, namely viscous boundary tractions, tied degrees of freedom and free field elements are reviewed. Possibilities and limitation of each type of boundary condition is highlighted. The formulation of a constitutive model, called as UBC3D-PLM, which describes the mechanical behaviour of soils under cyclic loading is also presented. The model is an extension of the two dimensional UBCSAND model developed at University of British Colombia which utilises isotropic and kinematic hardening rules for primary and secondary yield surfaces to properly take into account accumulation of excess pore water pressure and effect of soil densification during cyclic loading. By means of a simp lified Rowe’s stress-dilatancy theory, the model is capable of modelling liquefaction for different stress paths. It will be presented in this paper how most of the model parameters can be found from the corrected SPT blow count which makes the model easy to use for practical applications. Finally, the model is used for modelling a real boundary value problem and the results are compared with field measurements.

Random Wave-Induced Seabed Responses around Breakwater Heads

Y Zhang, D-S Jeng, Z-W Fu and J Ou

ABSTRACT: Wave-induced pore pressures and effective stresses in a porous seabed around breakwater heads have been recognised as one of the key factors in the design of breakwaters. Unlike previous investigations, which were limited to regular wave loading, this paper investigated random wave-induced seabed responses. Two common wave spectra, B-M and JONSWAP, were used for the simulation of random waves in a model. Based on this poro-elastoplastic model, the influence of random wave parameters, waves and seabed parameters on the pore pressures around breakwater heads were examined and discussed in detail.

Influence of brittle property of cement treated soil on undrained bearing capacity characteristics of the ground

S. Yamada, T. Noda, A. Asaoka and T. Shina

ABSTRACT: In this study, the influence of brittle property of geomaterials on the failure behavior of the ground in an undrained bearing capacity problem was investigated numerically from the standpoint of taking the brittle behavior of cement treated soil as softening behavior of the soil element. The numerical analyses were performed using the soil-water coupled finite deformation analysis code GEOASIA mounted with the SYS Cam-clay model, which describes the soil skeleton structure at work. Cement treated ground and naturally deposited clay ground were modelled and compared, and it was found that they showed widely differing failure processes depending on differing initial conditions. Especially, it was found that when progressive failure in which strain localization region develops due to propagation of material failure occurs, even though the ground is composed of brittle materials such as cement treated soil, those brittle properties do not directly manifest in the load-settlement relationship. Additionally, the investigation revealed that, since every soil element on the slip lines does not reach its peak strength simultaneously when progressive failure occurs, post -peak material properties, i.e. the ratio of residual strength to peak strength and softening rate from peak to residual state, affect the bearing capacity of the ground.

J.-C. Chai, J. P. Carter, A. Saito and T. Hino

ABSTRACT: The deformation of clayey soil subjected to the combination of a vacuum pressure and a surcharge load in an oedometer apparatus, with either vertical or inward radial drainage, has been investigated experimentally. A parameter Kw, defined as the horizontal effective stress exerted on the wall of the consolidation ring (s’hw) divided by the vertical effective stress (s’v) in the soil specimen is suggested as an indicator of the tendency for lateral deformation under field conditions. It is observed that if the value of Kw is close to the value of K0 of the soil (the ‘at-rest’ earth pressure coefficient), there should be very limited lateral displacement in field situations. The laboratory test results show that during the loading process, the value of Kw is mainly influenced by the ratio of the magnitude of the surcharge pressure to the vacuum pressure (RL) and the rate of surcharge loading (SLR). At the end of consolidation the value of Kw increases with increasing RL, but it is almost independent of SLR for the conditions investigated. In the presence of a vacuum pressure, at the end of consolidation the value of Kw is usually less than the original value of K0 of the soil. The test results also indicate that Kw has a strong correlation with the synthetic non-dimensional loading parameter, RLS, as defined by Chai et al. (2013), which includes the effects of both RL and SLR as well as the consolidation properties of the soil. It is suggested that the parameter RLS can be used to predict lateral displacements under field conditions that involve combined surcharge and vacuum pressure loading.

KEYWORDS: Vacuum consolidation, combined loading, oedometer, earth pressure, deformation

Behaviour of Geogrid Reinforced Abutments on Soft Soil

Ennio M. Palmeira, André R.S. Fahel and Gregório. L. S. Araújo

ABSTRACT: The behaviour of embankments on soft soils is a complex problem, particularly when the substitution of the soft material is not cost effective. In this case, the use of geosynthetics may be a feasible and economical solution for the stabilization of the embankment and reduction of the effects of differential settlements. This paper shows an investigation on the use of geogrid reinforcement in combination with pre-fabricated vertical drains (PVD) to accelerate soft soil consolidation in abutments for the duplication of the BR-101 highway, in Brazil. The instrumentation of bridge abutments included inclinometers, settlement and horizontal displacement plates, full-profile settlement gauges and piezometers, as well as strain gauges in the reinforcement layer. The results obtained showed that one of the abutments almost collapsed due to wrong construction practice and reinforcement specification. Insufficient reinforcement tensile force mobilization along the embankment transverse direction combined with wrong reinforcement orientation yielded to large embankment displacements and the initiation of failure. This failure mechanism could have been predicted with the use of current slope stability analysis for this type of problem. The results also showed the beneficial effect of the reinforcement for the stability of the embankment and reduction of lateral displacements of the abutments.

KEYWORDS: Reinforced abutments, soft soil, geogrid, stability, strains

Geocell-Reinforced Granular Fill under Static and Cyclic Loading: A Synthesis of Analysis

X. Yang and J. Han

ABSTRACT: Geocell is a three-dimensional geosynthetic that provides direct lateral confinement to the infill material. In recent years, the use of geocell-reinforced granular fill as a load supporting layer has received increased attention. In the past, lack of well-developed design methods that could quantify the benefit of geocell reinforcement limited the application. To fill the gap between the design and the application, fundamental, theoretical, and applied research projects have been carried out in several research institutes. This paper presents a synthesis of these studies on the analysis of geocell-reinforced granular fill. Due to the differences of soil behaviour under static and cyclic loading, theoretical and numerical analyses are summarized in this paper based on loading conditions. Experiments performed to facilitate the theoretical and numerical analyses are also reviewed. Recommendations are made for areas of future research.

KEYWORDS: Geocell, geosynthetic reinforcement, granular fill, static load, and dynamic load

Electrical Vertical Drains in Geotechnical Engineering Applications

J. K. Lee and J.Q. Shang

ABSTRACT: Electrical vertical drains (EVDs) have been applied for improvement of soft clays. In this state of the art review, an overview of the theory of electrokinetics is presented, followed by discussions of the characteristics and limitations of some EVDs via laboratory and field experimental studies on electrokinetic stabilization of geo-materials. The predominant mechanism of electrokinetic stabilization includes electroosmosis, the movement of pore water in soil driven by a direct current (DC), and electro cementation induced by electrochemical reactions at electrodes. The overall effect of electrokinetic treatment is the increase in the soil shear strength and decrease in the soil compressibility. The technique has been applied successfully in geotechnical engineering, while one of the challenges is corrosion of anodes that are typically made of steel or copper. More recently, conductive polymer products have been developed, such as electrokinetic geosynthetics (EKGs) and electrical vertical drains (EVDs). This paper presents case histories on using EVDs in soil improvement. The authors hope that this review serves as a guidance for future research and development of electrokinetic treatment of geo-materials using EVDs.

KEYWORDS: Electrokinetics, electrical vertical drains (EVDs), physiochemical properties, soil shear strength, and settlement

Design and Performance of Soft Ground Improvement Using PVD with and without Vacuum Consolidation

P.V. Long, D.T. Bergado, L.V. Nguyen and A.S. Balasubramaniam

ABSTRACT: This paper presents the soft ground improvement using Prefabricated Vertical Drains (PVD) including PVD installation and preloading techniques, settlement and stability design calculations, observational methods and back analyses of monitoring data and performance of conventional preloading with surcharge fill and preloading using vacuum consolidation method (VCM) in combination with fill embankment. Several case histories were studied. The monitored data illustrated that the effectiveness of VCM is dependent on the method of applying vacuum pressure to the PVDs. Measured pore pressure in the PVDs at different depths indicated that the effective vacuum pressure inside the PVDs is distributed uniformly along the PVD depth with a magnitude of over 80 kPa for VCM using airtight membrane. Back-calculated ch values from measured settlement data using Asaoka method confirmed that with the assumed values of ds/dm = 2 and kh/ks = 2, the corresponding value of ch/cv,oed = 3 to 5 were obtained for both soft Bangkok (BKK) clay and soft clays in Mekong River Delta (MRD). Also, the linear relationship between compression index and water content for soft clays in MRD is similar to that of BKK clay. The settlements versus time calculated by 1-D method are in very good comparison with measured data for both conventional preloading and VCM considering the vacuum pressure as an induced vertical stress distributed uniformly in the PVD zone. From the results presented in this paper, simple procedures can be made for selection of soil parameters and design calculations of embankments on PVD improved soft ground using conventional preloading and vacuum consolidation.

KEYWORDS: Settlement, stability, soft clay, ground improvement, PVD

Reassessment of Long-Term Performance of Geogrids by Considering Mutual Interaction among Reduction Factors

Han-Yong Jeon and Yuan Chun Jin

ABSTRACT: For estimating allowable tensile strength of geogrids by reduction factor, it has a limit not to consider interaction force among reduction factors. Junction strength would be reduced by installation damages or chemical degradation as same as tensile strength. Single junction test method cannot properly cover for damaged samples and shows large deviations as it does not consider scale effect. Especially for calculating shear strength, no reasonable study to consider all reduction factors was conducted yet. Therefore, in this study, (a) reduction factors that may affect the long-term performance of geogrids were revaluated to consider various application conditions and (b) accurate long-term allowable tensile strength was calculated to consider interrelation among reduction factors. Creep results after installation damage and chemical resistance test showed lower value than that of GRI GG-4 calculation. After installation damage and chemical resistance test, the reduction factor of junction strength was less than that of tensile strength. Finally, shear strength before and after installation damage showed no change before and after installation.

KEYWORDS: reduction factor, junction strength, scale effect, long-term performance, GRI GG-4

Simulations of PVD Improved Reconstituted Specimens with Surcharge, Vacuum and Heat Preloading using Axisymmetric and Equivalent Vertical Flow Conditions

P. Voottipruex and D.T. Bergado, and W. Wongprasan

ABSTRACT: This paper presents the simulations of prefabricated vertical drain (PVD) improved reconstituted specimens with surcharge preloading (PVD), vacuum and surcharge with PVD (Vacuum-PVD), heat and surcharge with PVD (Thermo-PVD), heat plus vacuum and surcharge with PVD (Thermo-Vacuum-PVD) from large scale consolidometer tests in the laboratory. The flow conditions included axisymmetric conditions with horizontal (Kh) and vertical (Kv) permeabilities as well as equivalent vertical permeability (Kev) using backcalculated coefficient of horizontal consolidation (Ch). The simulation results indicated that the settlements and excess pore pressures obtained from axi-symmetric and equivalent vertical flows were similar at the same ratio of horizontal permeability at undisturbed zone to horizontal permeability at smear zone (Kh/Ks). The back-calculated Ch values were 1.93, 2.23, 4.17 and 4.38 m2/yr as well as the corresponding Kh/Ks values were 3, 2.7, 1.4, and 1.1, for PVD, Vacuum-PVD, Thermo-PVD and Thermo-Vacuum PVD, respectively. The Ch values increased while the Kh/Ks values decreased corresponding to PVD, Vacuum-PVD, Thermo-PVD, and Thermo-Vacuum PVD, respectively.

KEYWORDS: Prefabricated vertical drains (PVDs), equivalent vertical permeability (Kev), heat and surcharge preloading, numerical simulation

Reinforced Embankments on Soft Deposits: Behaviour, Analysis and Design

C. Taechakumthorn and R.K. Rowe

ABSTRACT: This paper reviews the key mechanisms on how basal reinforcement improves embankment behaviour through an examination of cases where embankments were constructed on soft organic clay and peat. The embankment responses from undrained and partially-drained simulations are compared to highlight the effect of consolidation during the construction. The benefits from the combined use of basal reinforcement and PVDs are presented. This paper also provides an overview of a design approach for embankments on soft ground taking account the interaction between basal reinforcement and PVDs as well as explores the effect the time-dependent behaviour of geosynthetics and rate-sensitive soils on the long-term performances of reinforced embankment under working condition. The limitations of the current design method are discussed. Finally a case study involving a reinforced embankment constructed over soft sensitive clay with a weathered crust is presented to illustrate the effect a stiff crust and soil structure can have on the effectiveness of the basal reinforcement used for this particular case.

KEYWORDS: Reinforced embankment, soft soil, basal reinforcement, geotextiles, geogrids

Current State of the Art in Vacuum Preloading for Stabilising Soft Soil

C. Rujikiatkamjorn and B. Indraratna

ABSTRACT: In this paper the analytical solutions for radial consolidation that include time dependent surcharge loading and vacuum pressure are proposed, whilst also considering the impact of the parabolic variation of permeability in the smear zone. The use of the spectral method for multilayered soil consolidation is introduced and verified. The Elliptical Cavity Expansion Theory is used to predict the extent of soil disturbance (smear zone) caused by the installation of mandrel driven vertical drains. The predicted smear zone is then compared to the data obtained from large-scale radial consolidation tests. Furthermore, the advantages and limitations of applying a vacuum through vertical drains are discussed using the proposed solutions. The vacuum pressure applied generates a negative pore water pressure that increases the effective stress within the soil, which leads to an accelerated consolidation. Vacuum pressure is modelled as a distributed negative pressure (suction) along the length of the drain and across the surface of the soil. Analytical and numerical analyses that incorporate the Authors’ equivalent plane strain solution are conducted to predict the excess pore pressures, lateral and vertical displacement. The application of the theoretical models for selected case histories at the site of the 2nd Bangkok International Airport and the Port of Brisbane, are discussed and analysed. The predictions are compared with the available field data and show that the proposed model can be confidently used to predict the performance with acceptable accuracy through rigorous mathematical modelling and numerical analysis. The research findings verify that the role of the smear zone and vacuum distribution can significantly affect the consolidation of soil, but these aspects need to be modelled appropriately to obtain reliable.

KEYWORDS: Analytical modelling; case history; numerical modelling; vacuum consolidation; vertical drain

Jet Grouting Practice: an Overview

Z.F. Wang, S.L. Shen, C.E. Ho and Y.H. Kim

ABSTRACT: Jet grouting is one of the most popular ground improvement techniques due to its applicability in almost all soil types. In this overview, the historical progress of technology development in jet grouting is briefly described, followed by the trace of the development of empirical and theoretical approaches for predicting the achievable diameter of a jet grout column. This paper also introduces a recently developed jet grouting technique called the Twin-Jet method. Twin-Jet method was developed to achieve quick solidification of soft soils by jetting with two types of binders, cement-slurry and sodium silicate (water glass) as an accelerator. This technique is particularly advantageous in horizontal jet grouting applications. Two case histories are presented to demonstrate the performance of Rodin Jet Pile (RJP) method in the soft clayey and sandy soils in Shanghai and the application of the Twin-jet method in sandy soils in South Korea.

KEYWORDS: Soft deposit, Jet Grouting, Diameter, Twin-Jet, Two binders

Deep Mixing Method in Japan

Masaki Kitazume

ABSTRACT: The Deep Mixing Method (DMM), a deep in-situ soil stabilization technique using cement and/or lime as a stabilizing agent, was developed in Japan and in the Nordic countries independently in 1970s. Due to its wide applicability and high improvement effect, the method has gained increased popularity in many countries. The method has been successfully employed in thousands of projects and the volume of improved soil from 1977 to 2010 exceeded 100 million cubic meters in the Japanese market alone. In the past three to four decades, traditional mechanical mixing has been improved to meet changing needs. Also new types of technologies have been introduced in the last 20 years and put into practice; e.g. high pressure injection and hybrid of mechanical and high pressure injection. The design procedures for various infrastructures were standardized by responsible organizations in Japan and revised several times. The manuscript presents a State of the Art on the Deep Mixing methods in Japan that covers the machinery, design, construction and quality control and assurance of the Deep Mixing Method.

KEYWORDS: Ground Improvement, Deep Mixing Method, Design, Execution, Quality control and quality assurance

Recent Studies of Geosynthetic Tubes and Mattress: an overview

Wei Guo, Jian Chu and Shuwang Yan

ABSTRACT: Geosynthetic tubes have been used in recent years in many projects related to coastal protection, dike construction, flood control and waste sludge dewatering purposes. The geosynthetic mattress method that uses flat mattress like geosynthetic containers have also been developed and used in several projects. The applications of geosynthetic tubes and geosynthetic mattresses are summarized in this paper. The existing analytical methods for different kinds of geosynthetic tubes are also summarized and critically reviewed in this paper. Methods for experimental studies and numerical analysis of geosynthetic tubes and mattresses are also reviewed and discussed.

KEYWORDS: Geotextile tube, geosynthetic tube, geosynthetic mattress

Design Method for Bearing Reinforcement Earth Wall

S. Horpibulsuk, C. Suksiripattanapong and A. Chinkulkijniwat

ABSTRACT: The bearing reinforcement was developed as a cost-effective earth reinforcement. It is composed of a longitudinal member and transverse members. The longitudinal member is made of a deformed bar, which exhibits a high pullout friction resistance. The transverse members are a set of equal angles, which provide high pullout bearing resistance. The bearing reinforcement earth (BRE) walls have been applied as a bridge abutment and a retaining structure along mountainous areas in several projects of the Department of Highways, Thailand since 2008. Based on the laboratory and field studies and design experience, the design method of the BRE wall is presented. The examination of external stability is performed using the conventional method (limit equilibrium analysis) assuming that the composite backfill-reinforcement mass behaves as a rigid body. The internal stability deals with rupture and pullout resistances of the reinforcement. The pullout resistance of the bearing reinforcement is approximated using the modified punching shear mechanism. The maximum tension plane is the bilinear failure mechanism (coherent gravity structure hypothesis). Finally, a design procedure, which commonly used in Thailand, is summarized and suggested.

KEYWORDS: bearing reinforcement, inextensible reinforcement, mechanically stabilized earth wall, design method

Current State of Knowledge on Thermal Consolidation using Prefabricated Vertical Drains

H. M. Abuel-Naga, G. A. Lorenzo and D. T. Bergado

ABSTRACT: Several research works have demonstrated that subjecting normally consolidated clays to temperature less than the boiling point of water (100oC) will have positive effects on its hydro-mechanical behaviour. Such effects can be exploited in improving the performance of the well-known preloading ground improvement technique that utilizes prefabricated vertical drains (PVDs). In this review paper, the applicability of a novel prefabricated vertical thermal drain (PVTD) will be presented and discussed using results of large oedometer tests and full-scale embankment tests on soft Bangkok clay. The large oedometer test results gave promising outcomes since the temperature accelerates the rate of consolidation and increases the amount of total settlement. The viability of the proposed technique was also confirmed by the full-scale embankment test results. The success of the proposed technique can be attributed to the thermally induced volume change and the increase in the hydraulic conductivity as the soil temperature increases.

KEYWORDS: Thermal consolidation, temperature effects, Bangkok clay, prefabricated vertical drain (PVD), ground improvement

B. Mutlu Sumer

ABSTRACT: A review is presented of recent advances in seabed liquefaction and its implications for marine structures. The review is organized in seven sections: Residual liquefaction, including the sequence of liquefaction, mathematical modelling, centrifuge modelling and comparison with standard wave-flume results; Momentary liquefaction; Floatation of buried pipelines; Sinking of pipelines and marine objects; Liquefaction at gravity structures; Stability of rock berms in liquefied soils; and Impact of seismic-induced liquefaction.

KEYWORDS: Liquefaction, Waves, Marine structures, Seabed

Eulerian–Lagrangian Modeling of Current-Induced Coastal Sand Dune Migration

R. Sun, J. Wang, Y. Sakai and H. Xiao

ABSTRACT: In this work, an Eulerian–Lagrangian framework is developed for the modeling of current-induced sediment transport and sand dune migration. In this framework, the fluid flow is modeled by solving the Reynolds-averaged Navier–Stokes (RANS) equations, and a conservation equation is used to describe the morphological evolution of the sand bed, both of which are formulated in the Eulerian framework. Empirical models are used for the erosion, the dispersion, and the drag and lift forces exerted on the sediment particles. The trajectories of individual particles are tracked in the Lagrangian framework, which enables a high-fidelity representation of the particle motions and composition statistics, as well as direct representation of sediment deposition without the need of ad hoc models. This framework consists of four tightly coupled modules: (1) a fluid flow solver based on RANS equations, (2) a morphological evolution modeling equation, (3) a Lagrangian particle-tracking scheme for suspended sediments, and (4) a dynamic mesh motion solver which deforms the mesh to account for the effects of morphological evolution on the flow field. The developed framework is validated by using previous results in the literature and is used to simulate coastal sand dune formation migration. Favorable agreements with benchmark results are obtained, demonstrating potential of the developed Eulerian–Lagrangian modeling framework for sediment transport.

KEYWORDS: Sediment transport, Fluid–particle interaction, Computational fluid dynamics, Sand dune migration

Numerical Study of the Penetration Mechanism and Kinematic Behaviour of Drag Anchors Using a Coupled Eulerian-Lagrangian Approach

Haixiao Liu and Yanbing Zhao

ABSTRACT: The fundamental properties of drag anchors such as the movement direction of the fluke, the drag angle and drag force at the shackle and the anchor trajectory in soils are closely relevant to the penetration mechanism and kinematic behavior of the drag anchor during installation. In the present work, a large deformation finite element analysis using a coupled Eulerian-Lagrangian approach is performed to simulate the installation process of drag anchors with different fluke sections. The method for determining the reasonable mesh density and drag velocity is proposed based on the investigation on dependency of the numerical results on the mesh density and drag velocity. Through a systematic comparative study between numerical and theoretical analysis, clear knowledge of the movement direction, the drag angle and drag force at the shackle, the anchor trajectory, the effect of anchor geometry and the ultimate embedment depth of the anchor is obtained, which is beneficial to fully understanding the complex behavior of drag anchors in soils.

KEYWORDS: Drag anchor; Penetration mechanism; Kinematic behavior; Movement direction; Drag angle; Drag force; Trajectory; Coupled Eulerian-Lagrangian; Numerical

Cyclic Pore Pressure Generation in Silty Soils under the Action of Combined Waves and Current

Yi-Fa Wang, Fu-Ping Gao, and Wen-Gang Qi

ABSTRACT: Ocean waves and current always coexist in the offshore shallow water environments, which may bring the corresponding seabed responses more complex than those under pure waves. The responses of a silty soil under the action of combined waves and current were physically modeled with a specially designed water flume. A series of tests for the progressive waves with a following-current or with an opposing-current have been conducted, respectively. Both the water-surface elevation and the pore pressure, including the transient and residual components, at various depths in the silty soil were measured simultaneously. The effects of both wave loading history and superimposing current upon waves on the pore pressure responses are examined. It is indicated that the amplitude of the transient pore-pressure component is enlarged for the following-current case and reduced for the opposing-current case. The maximum amplitude of the residual pore-pressure component decreases gradually during the subsequent series of wave loading under the same wave conditions.

KEYWORDS: Pore pressure responses, Silty soil, Combined waves and current, Physical modeling

A Model for Predicting Pipeline Sinkage Induced by Tunnel Scour

Chengcai Luo, Hongwei An, Liang Cheng and David White

ABSTRACT: The current design practice for subsea pipeline on-bottom stability (e.g. DNV-RP-F109) does not account the effect of sediment transport around a pipeline. Both field survey and small scale model test results show that seabed scour has a significant effect on pipeline embedment and therefore stability. Physical model tests carried out in an innovative large experimental facility, named the O-tube, at the University of Western Australia, have shown that tunnel scour and the subsequent pipe sinkage into the scour hole tend to stabilize a pipeline which might otherwise become unstable on an assumed stationary seabed, under ramping-up flow conditions. A simple calculation model that incorporates the three-dimensional scour and pipe sinkage due to the soil bearing capacity failure at the supporting span shoulders is proposed. The model parameters were calibrated using the O-tube experimental results. The model serves as a key element of a new pipeline stability analysis method that takes into account seabed mobility.

KEYWORDS: Pipeline, On-bottom stability, Tunnel scour, Pipe sinkage

Predicting Spud Can Extraction Resistance in Soft Clay

Omid Kohan, Christophe Gaudin, Mark J. Cassidy, and Britta Bienen

ABSTRACT: Jack-ups are mobile offshore structures that are frequently relocated to new operation sites. To be relocated, the jack-up footings, known as spudcans need to be extracted from the seabed, using essentially the buoyancy of the hull as extraction force. This operation may be time consuming or even jeopardised if the spudcan extraction resistance is higher than the available extraction force. The maximum extraction (or breakout) resistance consists of suction at the spudcan base, weight of the soil above the spudcan, and soil shear resistance above the spudcan, with the contribution of the suction at the spudcan invert being the dominant component of the breakout resistance. This paper reviews an existing prediction method used to estimate spudcan extraction resistance and proposes an update of some of the input parameters based on insights obtained from a large database of experimental model data on two types of clays and for spudcan embedment up to three diameters.

KEYWORDS: Spudcan, Extraction resistance, Centrifuge modelling, Soft clay, Prediction method

A FE Procedure for Foundation Design of Offshore Structures – Applied to Study a Potential OWT Monopile Foundation in the Korean Western Sea

H.P. Jostad, G. Grimstad, K.H. Andersen, M. Saue, Y. Shin, and D. You

ABSTRACT: A finite element based calculation procedure that accounts for the effect of cyclic loading of soils under undrained conditions is presented. A material model called UDCAM that uses 3D strain contour diagrams from undrained cyclic and monotonic triaxial and DSS tests is used in the procedure. The model accounts for cyclic degradation by using the cyclic strain accumulation procedure developed at NGI in the seventies. The load history is idealized by a load composition containing load parcels with constant average and cyclic loads in each parcel. The applicability of the procedure is verified by back calculating a model test of a gravity base structure (GBS) in soft clay subjected to monotonic and cyclic loading. The procedure is then used to predict the behaviour of a monopile for a potential offshore wind turbine (OWT) in the Korean Western Sea. These results are compared with results obtained with traditional beam-spring analyses.

KEYWORDS: Offshore Engineering, Numerical modelling, Soil/structure interaction, Cyclic Loading, Clays, Monopiles, Wind Turbines

Compressibility as an Indicator of Liquefaction Potential

M. Murat Monkul, Poul V. Lade, Ehsan Etminan, Aykut Senol

ABSTRACT: It is difficult to impossible to obtain intact samples of loose, silty sand from coastal and offshore sandy soil deposits, which could potentially liquefy. To evaluate the liquefaction potential for such soils, a quantity that may be used as an indicator and can be measured in-situ is the volume compressibility. The more compressible the easier the soil will liquefy. Presented here is a study of three clean sands with the same geologic origin: Sile Sand 20/30, Sile Sand 50/55 and Sile Sand 80/100. Sile Sand 80/100 is also mixed with two types of non-plastic silts: TT Silt and IZ Silt. Three different fines contents of 5%, 15% and 25% are used for each of the two combinations of silty sands. Isotropic compression tests and undrained triaxial compression tests have been performed on these soils to determine their liquefaction potential and their compressibilities, and these are correlated with each other. Experiments have shown that volumetric compressibilities increase with increasing fines content for both silt types, which is similar to the observation of increasing liquefaction potential with fines content. Approximate boundaries for stable response, transition stage, and liquefaction region are determined. Accordingly, specimens with volumetric compressibility values smaller than 0.17 (1/MPa) were stable, while all specimens with volumetric compressibility values greater than 0.23 (1/MPa) liquefied. Further laboratory and in-situ tests on different sand and silt types are still needed to verify and tune those boundaries, which could potentially serve as indicators of liquefaction potential via in-situ compressibility tests.

KEYWORDS: Compressibility, Fines, Instability, Silty sand, Static liquefaction, Triaxial tests

Centrifuge Modelling of the Seismic Responses of a Gently Sloped Liquefiable Sand Deposit Confined within Parallel Walls

C.J. Lee, W.Y. Chung, and W.Y. Hung

ABSTRACT: A series of one-dimensional (1-D) centrifuge shaking table tests was performed to investigate the seismic responses of a 4° sloped liquefiable sand deposit confined within parallel walls, having various penetration depths and row distances, and with different fixed ends. The parallel walls relieved the build-up of excess pore water pressure in the deeper enclosed sand layer, but no obvious reductions were observed in the excess pore water pressure in the shallower sand layer during large earthquakes. The effective relief of the excess pore water pressure and decrease in the surface settlement within the walls would be expected to improve at deeper penetration depths and for higher wall bending stiffness values. Stiffer parallel walls with fixed ends can constrain the enclosed sands more effectively and prevent lateral displacement induced by lateral spreading occurred in gently sloped ground. The walls can also transmit larger accelerations into the enclosed soils. Protected structures would not, therefore, come in contact with the parallel walls, thereby avoiding experiencing larger accelerations.

KEYWORDS: Parallel walls, Liquefaction, Lateral spreading, Centrifuge modeling, Shaking table test

Eulerian Finite Element Analysis for Uplift Capacity of Circular Plate Anchors in Normally Consolidated Clay

Z. Chen, K. K. Tho, C. F. Leung and Y. K. Chow

ABSTRACT: Anchors are often used to provide uplift resistance for mooring of boats and floating decks as well as anchoring of pipelines offshore. Anchor is often idealized as a circular plate in the analysis of its uplift resistance. The uplift capacity of circular plate anchor in uniform soil is well documented in the literature. However, the pullout behavior of circular anchor in nonhomogeneous soil is less well studied and forms the motivation of this paper. In order to circumvent computational difficulties associated with severe mesh distortion during the pullout process, the Eulerian large strain, large deformation finite element approach is adopted in this study to investigate the pullout behavior of circular plate in normally consolidated clay. The applicability of the Eulerian numerical model is validated by comparing the numerical results with analytical solutions from lower bound limit analysis for a uniform soil as well as data for a centrifuge test conducted in normally consolidated Kaolin clay. Conventionally, it is generally accepted that the uplift behavior of a plate anchor in a normally consolidated soil can be inferred from that in a uniform soil by adopting the strength at the initial plate position as the reference strength. However, it is observed from the numerical results that the failure mechanisms corresponding to plate anchors in uniform clay and normally consolidated clay are different for the same set of reference undrained shear strength and geometric parameters. This implies that the conventional approach is not always applicable. A direct design method for obtaining the uplift capacity of a circular plate anchor embedded in a linearly increasing soil shear strength profile is then proposed.

KEYWORDS: Eulerian finite element, circular plate anchor, normally consolidated clay

Restoration Method of Artificial Tidal Flat by Use of Pressure Injection of Slurry Dredge Clay

Takahiro Kumagai, Takashi Tsuchida, Changjin Ko and Hiroaki Sugihara

ABSTRACT: The method of uplifting the ground surface by pressure injection of slurry dredge clay is proposed to restore the settled tidal flat without influencing the creatures living on and inside it. In order to establish the method, the study was carried out to examine the effectiveness of several technologies to uplift the ground smoothly avoiding the blowout of injected soil. As a result of laboratory experiment, it turns out that prior softening of original ground horizontally and placement of uplift restraint are effective for the purpose. The applicability of the proposed method was verified in situ contributing to the future practical application of technology by a field experiment.

KEYWORDS: Consolidation settlement, Dredged soil, Clam

Tsunami-Seabed-Structure Interaction from Geotechnical and Hydrodynamic Perspectives

S. Sassa

ABSTRACT: The paper reports some recent research advances on tsunami-seabed-structure interaction following the 2011 off the Pacific Coast of Tohoku Earthquake Tsunami, Japan. It presents a concise review of the latest research performed on the stability of breakwater foundation under tsunami by utilizing a geotechnical centrifuge and a large-scale hydro flume at Port and Airport Research Institute. I highlight here the role of tsunami-induced seepage in piping/boiling, erosion and bearing capacity decrease and failure of the rubble/seabed foundation. A comparison and discussion are made on the stability assessment for the design of tsunami-resistant structures on the basis of the results from both geo-centrifuge and large-scale hydrodynamic experiments.

KEYWORDS: Breakwaters, Geo-centrifuge, Large-scale hydro flume, Seepage, Tsunami

Feature Story on “Challenges in the Design of Tall Building Foundations”

Harry G. Poulos

ABSTRACT: This paper reviews some of the challenges that face designers of foundations for very tall buildings, primarily from a geotechnical viewpoint. Some characteristic features of such buildings will be reviewed and then the options for foundation systems will be discussed. A three-stage process of foundation design and verification will be described, and the importance of proper ground characterization and assessment of geotechnical parameters will be emphasized. The application of the foundation design principles to meet the challenges will be illustrated via three high-rise projects.

KEYWORDS: Case histories; design; foundations; piles; piled raft; settlement; tall buildings