State-of-the-Art Research in Geo-energy and Geo-environmental Engineering: Energy Pile and Earthen Capillary Landfill Cover System
By Charles W.W. Ng, Jason L. Coo & Anthony Gunawan
ABSTRACT: Geo-energy and geo-environment are two branches of geotechnical engineering representing current and future grant challenges because of the pressing need to conserve energy and protect the environment. The Hong Kong University of Science and Technology has been actively seeking solutions to these two challenges. The first part (geo-energy) of this paper describes a series of novel cyclic heating and cooling centrifuge tests performed on replacement and displacement floating energy piles installed in both saturated sand and clay. The test results reveal that replacement floating energy piles exhibit ratcheting settlement under a constant working load but at a reducing rate when subjected to temperature cycles, irrespective of the type of soil in which they are embedded. On the contrary, displacement floating energy piles exhibit heave behaviour. No existing theoretical model can capture observed ratcheting pile settlement well. This suggests that care must be taken when designing replacement floating energy piles. In the second part (geo-environment) of the paper, a novel three-layer environmentally friendly earthen cover system for climate regions like Thailand, Indonesia, the Philippines, Malaysia and Singapore is investigated through theoretical examination, physical modelling (e.g., one-dimensional soil column and two-dimensional large flume tests), and advanced numerical simulations. This novel cover system consists of a fine-grained soil underneath a conventional two-layer cover with capillary barrier effects. Two-dimensional water infiltration experiments and numerical simulations show that the newly introduced fine-grained soil layer can greatly minimize rainfall infiltration even after a 4-h rainfall event having a return period of 100 years in climate regions. One-dimensional gas emission tests and numerical simulations reveal that a minimum of 0.6 m thick fine grained soil layer compacted at 10% saturation (e.g. those in arid regions) can adequately satisfy the Australian guidelines. No geomembrane is needed. This new environmentally friendly and robust earthen landfill cover system is thus a promising alternative to other landfill covers for minimizing rainfall infiltration and landfill gas emission under all kinds of weather conditions.
KEYWORDS: Geo-energy, Geo-environment, Energy Pile, Landfill cover system
Validation of a New Simplified Hypothesis B Method for Calculating Consolidation Settlement of Clayey Soils Exhibiting Creep
By J.-H. Yin and W.-Q. Feng
ABSTRACT: This paper introduces a new simplified Hypothesis B method for calculating consolidation settlement of clayey soils exhibiting creep. The general equations of the new simplified Hypothesis B method are presented and explained firstly. After this, four different cases are used to examine the validation of this new method. The four cases are: (i) a single layer of clay with laboratory test data, (ii) one layer of Hong Kong Marine Deposits (HKMD) with three different over-consolidation ratios (OCRs), (iii) one layer of HKMD with vertical drain, and (iv) two layers of HKMD and Alluvium. The fully coupled consolidation analyses of all four cases are done by using one commercial FE program using a soft soil model, one in-house developed FE program and a finite difference method using Yin and Graham’s Elastic Visco-Plastic (EVP) model. The consolidated settlements of the same cases are also calculated using the new simplified Hypothesis B method and Hypothesis A method and are compared with values from numerical methods. The relative errors are calculated by using the FE results as reference. It is, from the above validation cases, found that the settlements calculated using the new simplified Hypothesis B method are closer to test data or the values from the fully coupled finite element (or finite difference) analyses with the least relative errors. Hypothesis A normally under-estimates the settlement a lot with the largest errors. The main conclusion is that the new simplified Hypothesis B method is very suitable for calculating consolidation settlement of clayey soils exhibiting creep and is easy to use by simple spreadsheet calculation.
KEYWORDS: Creep, Hypothesis A, Hypothesis B, Clay, Consolidation, Settlement, Vertical drain
Finite Element Analysis to Characterize the Lateral Behaviour of a Capped Pile Group
By Chao-Kuang Hsueh, San-Shyan Lin and Dominic E. L. Ong
ABSTRACT: Finite element simulation for analysis of a capped pile group was conducted to investigate the interaction among piles, soil and pile cap, especially the effects resulted from concrete damaging. The simulation was to develop a calibrated model using the test data and to apply that model for conditions not present during the test. In addition to consider pile/soil and cap/pile interaction in the numerical simulation, interaction between steel reinforcement and concrete was also modelled in the analysis. Each steel reinforcement installed in the tested piles and the pile cap was modelled as an individual element at its installed position in the numerical analysis. The simulation results showed that the leading and the middle row piles in the group carried the highest and the lowest fraction of pile head loads when concrete around the pile cap/soil contact area remained its integrity. Increasing loading level, the pile head load carried by the middle row increased due to constraint of the pile cap affected by the concrete damage at the pile cap/soil contact zone.
KEYWORDS: Pile group, Lateral pile loading test, Finite element analysis, Concrete cracking, Soil-pile interaction.
Proposed Design Guideline of Dynamic Compaction for Practicing Engineers
By Tjie-Liong Gouw
ABSTRACT: During an earthquake, saturated fine sands tends to lose its bearing capacity due to the earthquake induced and accumulated excess pore water pressure. The phenomenon, known as liquefaction, is one of the earthquake hazards that need to be mitigated in an earthquake prone area such as the archipelagos of Indonesia. The occurrence of an earthquake cannot be prevented and, with the present knowledge, is difficult – if not impossible – to predict. However, liquefaction potential can be mitigated by carrying out proper ground improvement methods. The most common ground improvement schemes that have been widely implemented in mitigating liquefaction potential of saturated fine sands in Indonesia are dynamic compaction and vibro-compaction. However, many practicing engineers are still not familiar with the methods. This paper presents the design, execution, and evaluation methods of dynamic compaction. Two case histories on real projects are also presented as examples.
KEYWORDS: Dynamic compaction, Design guideline
Settlement of River Dykes and Their Adjacent Residences on Soft Clay Deposits After the Tohoku-Pacific Ocean Earthquake in 2011
By K. Yasuhara, S. S. Yang, I. Horikawa and H. Yamane
ABSTRACT: Among the extensive infrastructure collapses which resulted from the cataclysmic earthquake that struck off the eastern coast of Japan on March 11, 2011, long-term settlement and deformation of clay deposits during the earthquakes has sometimes been overlooked. This paper describes a case history of post-earthquake settlement of clay deposits underlying river dykes and their adjacent residences. Particularly, an attempt is made to assess reactive countermeasures designed to mitigate damage from such settlement and deformation.
KEYWORDS: Land subsidence, Earthquake, Clay deposit, Countermeasure
Application of Photogrammetry and Image Analysis for Rock Slope Investigation
By D-H. Kim, A. S. Balasubramaniam and I. Gratchev
ABSTRACT: This study reviews the applications of close range photogrammetry (CRP) on modelling for rock slope stability analysis and weathering investigations focussing on the applicability of CRP to obtaining roughness characteristics. Current photogrammetric techniques have a potential to provide roughness profiles with dense measurement intervals. However, the quality of the roughness data is still questionable and the level of accuracy has not been sufficiently investigated. To advance the boundaries of the availability of CRP, this paper presents methodologies which can quantify the degree of accuracy for the obtained roughness data and to detect the data noise as an evaluation tool. Firstly, this study suggests an error model which measures the level of accuracy based on an ideal lab condition. The level of accuracy of rock joint roughness coefficient (JRC) obtained from CRP can be interpreted by using the developed error model. Secondly, this paper presents an image analysis workflow via a MATLAB image filtering code for the estimation of recession areas focussing on the variation of rock surface roughness. This post-process of CRP supports more reliable interpretation of photogrammetric roughness data. The developed error model and the combined image analysis with 3D photogrammetric models could compensate the limitations of the uses of both digital photographs and 3D surface models to obtain roughness characteristics and for quantifying weathering patterns.
KEYWORDS: Photogrammetry, Rock surface roughness, Image analysis, MATLAB, Weathering.
Longitudinal and Transverse Interactions between Stacked Parallel Tunnels Constructed using Shield Tunnelling in Residual Soil
By C.W. Boon and L.H. Ooi
ABSTRACT: In the construction of stacked parallel twin tunnels, the lower tunnel is normally constructed first before the upper tunnel to minimise the impact to the first tunnel due to the construction of the second tunnel. This paper examines the special case in which the upper tunnel was constructed first and undermined subsequently in a parallel configuration during the construction of the lower tunnel using shield tunnelling in residual soil. The longitudinal settlement profile of the upper tunnel due to the undermining by the lower tunnel was studied analytically using Winkler beam solutions, and the results were compared with field measurements through a case history. As the twin tunnels transitioned from a stacked configuration into a skewed configuration, the settlement of the upper tunnel was studied using several common solutions in engineering practice, such as cavity expansion, Gaussian settlement solutions and finite element analyses. The discrepancies between the closed-form solutions and field measurements were found to be largely due to the influence of the lateral earth pressure coefficient, K0<1. According to the finite element analyses, the in-situ stresses with K0<1 had a competing deformation mechanism with the settlements induced by tunnelling volume losses. Comparison was carried out against the conventional tunnelling sequence in which the lower tunnel was constructed first, the results of which revealed deformation magnitudes more than five times smaller, underscoring the need for detailed analyses for tunnelling sequences in which an existing tunnel is undermined. Equations to estimate the subsurface Gaussian trough width parameter from a pair of extensometer readings were derived and presented in the Appendix. Nonetheless, the extensometer measurements were localised and may not be representative of the entire geological formation.
KEYWORDS: Tunnel interaction, Stress ratio, Winkler beam, Undermining, Settlement
Common Blind Spots in Ground Investigation, Design, Construction, Performance Monitoring and Feedbacks in Geotechnical Engineering
By Shaw Shong Liew
ABSTRACT: In geotechnical engineering dealing with risks and uncertainties, the processes involved start from the investigation with the fundamental intention to attain better understanding of the subsurface conditions and acquisition of the engineering parameters for the subsequent engineering analyses, designs, detailing, tender documentation and calling, followed by design validation tests at field and construction problem solving. With the forensic investigation experiences by the author in the past, some interesting findings and surprises are compiled in this paper to illustrate these common blind spots at the aforementioned engineering processes. The importance of desk study and sound geological knowledge in planning of investigation programme have not received sufficient emphasis in the higher education system, thus resulting in significant wastage by the trained graduate in using the investigating tools and generating excessive amount of redundant information. Some of the mistakes are fundamental errors in perceiving the engineering behaviours when using the software with intuitive and illusive perception rather than based on sound engineering understanding. There is also strain compatibility issue in mobilising material strength of composite materials with drastic stiffness contrast when approaching failure state of a soil structure interaction problems. Design validation tests are crucial to ensure design methods adopted able to reasonably behave as intended. However, the tests usually do not reveal the overall behaviours of the design in actual scale and time factors, but rather a behaviours of a special case or prototype. Geotechnical instrumentation on a larger scale with time might be a more representative of practical performance with totality. This will be more useful for review and back-analysed of a big picture performance of the geotechnical structures.
KEYWORDS: Mechanism, Forensic investigation, Case study, Soil structure interacti
Detrimental Effects of Lateral Soil Movements on Pile Behaviour
By D.E.L. Ong
KEYWORDS: Limiting soil pressure; Soil movements; Soil-structure interaction; and Riverbank.
Optimising Cement Dosage in Ground Improvement and Early Quality Control Schemes
By S.C. Chian
ABSTRACT: Judicious dosage of cement in soft clayey soils is key in reducing waste, time and cost in this growingly environmental conscious modern society. Despite being a well-established technique in ground improvement, studies on the prediction of strength development of cement stabilised soils are often limited to a couple of clay types or site specific. This paper presents an extensive suite of unconfined compressive strength tests of cement-mixed clayey soils over a wide range of mix ratios, curing ages and sand impurities. A strength predictive model encompassing the above variables was developed and validated with several types of clay and cement from different sources. This enables the optimisation of cement dosage to achieve a desirable unconfined compressive strength to satisfy the ground improvement criteria with ease. Quality control schemes using early age strength and portable bender element were also discussed in this paper.
KEYWORDS: Soft clays, Cement stabilisation, Unconfined compression test, Mixing ratio, Curing age, Quality control
Effects of Preloading of Struts on Retaining Structures in Deep Excavations
By Richard N. Hwang and Lup-Wong Wong
ABSTRACT: The performance of an excavation of 19.4 m in depth in soft ground has been reviewed by interpreting the readings of inclinometers in wall of 35 m in length and strain gauges in six levels of struts. Assuming the wall deflections at the first strut level would not move after preloading, the corrected inclinometer readings show that the deflections at the wall toes and at the tips of inclinometers were as much as 43 % and 25 % of the maximum wall deflections respectively. The large toe and tip movements are verified by numerical analyses, which have been conducted to study the effects of preloading of struts as well. The strain gauge readings show that the preloads applied to the struts do not sustain and drop significantly after subsequent preloading of struts. Four cases, namely, struts with full preloads, 50% preload to the first strut level, zero preload and actually observed preloads, have been adopted in the analyses to evaluate the effects of preloads. The results of the numerical analyses using the Mohr-Coulomb model are then compared with the observed wall deflection profiles in the final excavation stages. The Young’s moduli for clay and sand layers have been correlated with the soil strengths. It is found that computed peak strut loads are in agreement with the observed peak loads for the upper 3 levels of struts. For the lower 3 levels, the computed strut loads are however as much as 50% larger than those observed.
KEYWORDS: Deep excavation, Struts preloading, Wall deflections, Numerical analyses.
Anchors of Anchored Slopes in Taiwan
By Hung-Jiun Liao, Shih-Hao Cheng and Chun-Chung Chen
ABSTRACT: A catastrophic failure of an anchored cut slope at the national expressway in 2010 uncovered the status quo of tie-back anchors in Taiwan. Serious corrosion of anchor components due to poor corrosion protection was found to be the most obvious factor contributing to this landslide among other factors. After an extensive island-wide investigation on the existing anchored slopes, similar corrosion problem was found in many other anchored slopes. After the investigation, the construction and maintenance practice of anchored slopes had been fundamentally changed in Taiwan. This paper covers the inspection results on anchored slopes and also the measures taken to improve the corrosion protection of existing anchors and new anchors. Based on the problems found from the existing anchored slopes, some modifications on anchor tendon assembly and cement grouting practice had been developed to upgrade the corrosion protection of the new anchors and to monitor the long-term anchor load change as well.
KEYWORDS: Ground anchor, Corrosion, Remedial measures, Anchored slopes
Hexagonal Wire Mesh Panel Tensile Behaviour due to Weaving Patterns
By Chiwan Hsieh, Zhi-Yao Cai, and Wen-Shin Shuy
ABSTRACT: The tensile engineering properties of a commonly used wire mesh (120mm x150mm, ψ=4.0mm) with triple-twist (Type A) and fourth-twist (Type B) weaving methods according to the ASTM A975 test standard are studied. Wire mesh panel tensile tests loaded in the longitudinal and transverse directions with and without centre cut wire conditions and panel connection to selvedge tests were evaluated. Generally, the longitudinal tensile strengths were higher than that for the transverse tensile strengths. The Type B panel longitudinal and transverse direction tensile strengths and connection to selvedge strengths were all greater than those for Type A panel. In addition, the Type B panel showed better strength retention rates than the Type A panel with and without centre cut wire condition. The Type B panel showed better tensile behaviour than the Type A panel.
KEYWORDS: Hexagonal wire mesh, Gabion, River bank protection, Slope stabilization, Rock-fall protection.
Trenchless Excavations for Underground Pipelines in Difficult Geology
By Keh-Jian Shou, Jonas Yen, and Chih-Ying Hsieh
ABSTRACT: No-Dig constructions in the city might encounter various difficulties. And the difficulties or obstacles, which might cause schedule delays and damage to the pipes. Among the others, the conditions of overcut and stuck could be the most common and critical to a pipejacking project. This study considered various difficult conditions, including different overcut range and sticking position, together with different resistance, jacking force, etc. The ABAQUS finite element software was applied for three-dimensional numerical simulations for pipe-jacking with different difficult situations. The analyses focused on the pipejacking in gravel formations, and the suggestions were concluded based on the results. The results suggest that the location of sticking and its severity (different frictional coefficient was set) affect the stress field in the pipe. And the worst condition, i.e., the totally stuck, the adjacent soil and pipe will experience excessive deformation, which must be avoided. Therefore, lubrication to avoid this extreme scenario is essential in the pipejacking operation. For the case with large diameter, unavoidable overcut and highly variable geology, the above suggestions are more crucial.
KEYWORDS: Pipejacking, No-Dig, Difficult geology, Numerical analysis, Soil-pipe interaction
Liquefaction-Induced Settlement of Structures on Shallow Foundation
By C.W. Lu, L. Ge, M.C. Chu, and C.T. Chin
ABSTRACT: Unlike the liquefaction potential assessment, the liquefaction-induced ground settlement has not been studied extensively. The uncertainty of the ground profile and associated soil engineering properties is the major challenging to advance the current knowledge on this subject. Within Ishihara and his colleagues’ framework, the liquefaction-induced settlement is computed by the associated post-liquefaction volumetric strain, once the factor of safety for liquefaction is evaluated. For estimating settlement of a building with shallow foundation in liquefiable soils, on the other hand, dynamic behavior of the soils, its relative density, and the thickness of liquefiable soil, building’s weight and dimensions, seismic intensity, and structure-soil interaction should be considered accordingly. This paper aims to develop a practical and simple procedure to estimate the liquefaction-induced settlement on structures on shallow foundation, based on the framework proposed by Sawicki and Mierczynski in 2009. A series of comprehensive numerical analyses were carried out to incorporate the above-mentioned factors in the developed procedure. Data of liquefaction-induced settlement of structures on shallow foundation reported in the literature were used to compared with the estimated ones.
KEYWORDS: Liquefaction-induced settlement, Shallow foundation, Finite element analysis
Evaluation of Failure of Embankment Slope Constructed with Expansive Soils
By Kuo Chieh Chao, Jong Beom Kang and John D. Nelson
ABSTRACT: Slope failures in embankments constructed in expansive soils are often induced by rainfall infiltration during wet seasons or after a heavy rainfall event. Field investigations regarding the effect of rainfall infiltration on slope instability for expansive soil embankments indicate that shrinkage cracks developed during the drying and wetting cycles play an important role in slope instability. The excessive amount of infiltration through the shrinkage cracks decreases the matric suction of the expansive soil, and hence, results in a reduction of the shear strength of the soil accompanied with soil expansion, or heave. Furthermore, the modulus of elasticity of the soil decreases as water content increases and the soil heaves. The influence of these factors on the slope stability of expansive soil embankments is reviewed and discussed in the paper. Numerical modeling using the finite element computer programs SEEP/W and SIGMA/W was conducted to evaluate the volume change of an expansive soil embankment slope due to changes in suction arising from infiltration. Long-term stability of the expansive soil embankment slope was conducted using the computer program SLOPE/W. The expansive soil slope was also analyzed with a proposed remediation scheme to evaluate the effect of the remediation on long-term stability. The results of the numerical modeling for the slope with remediation were compared to those obtained for the slope without remediation. Furthermore, heaving of the expansive soil is accompanied by a reduction in the shear strength of the soil. Therefore, analysis of heave using the oedometer method was discussed in the paper. The results of the heave prediction using the oedometer method were compared to those obtained from the numerical modeling method. Reasons for the differences in amounts of predicted heave using both methods are discussed in the paper.
KEYWORDS: Expansive soil embankment slope, Heave prediction, Numerical modeling, Modulus of elasticity, Shear strength
Strength and Stiffness Parameters of Bangkok clays for Finite Element Analysis
By Suched Likitlersuang, Chhunla Chheng, Chanaton Surarak and Arumugam Balasubramaniam
ABSTRACT: Constitutive soil model and its parameters are the important issue in finite element analysis. Hardening soil model and Mohr-Coulomb model parameters of Bangkok clays for finite element analysis were evaluated in this study. To achieve this purpose, a case study of Sukhumvit MRT Station was selected to model in three dimensions with hardening soil and Mohr-Coulomb models. The instrumented data during construction was used to compare with the results from finite element analysis. PLAXIS 3D software was adopted as solving tool in this study. Lateral wall movement and ground surface settlement predictions were used to compare with the data. The outcomes were concluded that the hardening soil model characterised the Bangkok clay better than Mohr-Coulomb model in 3D finite element analysis for excavation.
KEYWORDS: Finite element analysis; Constitutive soil model; Deep excavation; Lateral wall movement; Ground surface settlement
Failure of Riverbank Protection Structure and Remedial Approach
By S. Horpibulsuk, A. Udomchai, M. Hoy, A. Chinkulkijniwat, and D. B. Van
ABSTRACT: This paper presents the case study of the collapsed riverbank protection structure along the Pasak river in Saraburi province, Thailand. The site investigation and finite element analysis using PLAXIS 2D results show that the failure occurred in sliding mode due to the natural forces. During the rainy season, water flow from the farmlands to the river by crossing the backfill of the retaining wall. Hence, seepage force was developed in the direction of the flow and induced the stability of the riverbank protection. Furthermore, the rivers and streams continuously scour the banks and undermined the natural slope, which caused the soil erosion in passive zone and resulted in instability. Based on these causes of failure, a new reinforced retaining wall structure using bored pile, geocomposite, and riprap at the front of retaining wall to protect the circular failure mechanism, seepage forces, as well as soil erosion and sedimentation, respectively was designed. The finite element verification on the new retaining wall structure showed that this structure had a sufficient factor of safety against the external and internal slope failure.
KEYWORDS: Riverbank protection structure, Seepage flow, Erosion, Finite element analysis
On Prefabricated Vertical Drain (PVD) and Deep Cement Mixing (DCM) / Stiffened DCM (SDCM) Techniques for Soft Ground Improvement
D. T. Bergado, P. V. Long, P. Jamsawang, C. Na Lampun, and A.S. Balasubramaniam
ABSTRACT: Soft ground improvement techniques have become most practical and popular methods to increase soil strength, soil stiffness and reduce soil compressibility including the soft Bangkok clay. This paper focuses on comparative performances of prefabricated vertical drain (PVD) using surcharge, vacuum and heat preloading as well as the cement-admixed clay of Deep Cement Mixing (DCM) and Stiffened DCM (SDCM) methods. The Vacuum-PVD can increase the horizontal coefficient of consolidation, Ch, resulting in faster rate of settlement at the same magnitudes of settlement compared to Conventional PVD. Several field methods of applying vacuum preloading are also compared. Moreover, the Thermal PVD and Thermal Vacuum PVD can increase further the coefficient of horizontal consolidation, Ch, with the associated reduction of kh/ks values by reducing the drainage retardation effects in the smear zone around the PVD which resulted in faster rates of consolidation and higher magnitudes of settlements. Furthermore, the equivalent smear effect due to non-uniform consolidation is also discussed in addition to the smear due to the mechanical installation of PVDs. In addition, a new kind of reinforced method, namely: Stiffened Deep Cement Mixing (SDCM) pile is introduced to mitigate the problems of the Deep Cement Mixing (DCM) pile due to the low flexural resistance, lack of quality control in the field and, consequently, unexpected failures. The SDCM pile consists of DCM pile reinforced with precast reinforced concrete (RC) core pile. The full scale test embankment on soft clay improved by SDCM and DCM piles was studied. Numerical simulations using the 3D PLAXIS Foundation finite element software have been done to understand the behavior of SDCM and DCM piles. The simulation results indicated that the surface settlements decreased with increasing lengths of the RC core piles, and, at lesser extent, increasing sectional areas of the RC core piles in the SDCM piles. In addition, the lateral movements of the embankment decreased by increasing the lengths (longer than 4 m) and, the sectional areas of the RC core piles in the SDCM piles. The results of the numerical simulations closely agreed with the observed data and successfully verified the parameters affecting the performances and behavior of both SDCM and DCM piles.
KEYWORDS: Ground improvement, PVD, DCM pile, SDCM pile, Soft clay, Laboratory test, Full scale test.
Study on Shield Operation Method in Soft Ground by Shield Simulation
By Mitsutaka Sugimoto, Hideyuki Tanaka, Ngoc Thi Huynh, Salisa Chaiyaput, Le Gia Lam, and Jian Chen
ABSTRACT: Shield tunneling technologies have been developed for constructing tunnels in soft ground especially under groundwater. Recently, challenging projects from the viewpoint of tunneling technology have been planned. To realize these constructions, it is necessary to examine the shield operation method preliminarily. The authors have developed a method to carry out the above examination and have confirmed its validity for a tunnel in stiff ground. In this research, to examine the performance of the proposed method for soft ground tunnel, the simulation on shield behavior was carried out using the estimated shield operational data for a tunnel in soft ground. As a result, the following were found: the shield steering conditions by the proposed method are not enough to rotate the shield along a sharp curve in case of soft soil; and the simulation results have a good agreement with the planned alignment using proper shield operational data.
KEYWORDS: Shield tunneling method, Kinematic shield model, Articulated shield, Steering, Numerical simulation
