Centrifuge Modelling of Improved Ground
M. Kitazume, Y. Morikawa and S. Nishimura
ABSTRACT: Soft soil is often encountered during infrastructure construction, in which large ground settlement and stability failure can be anticipated. There are many soil improvement techniques in existence to counter these problems. The behaviour of improved ground is affected by many factors such as the physical and mechanical properties of the original ground and the improved ground, interaction of the original and improved ground, external loading conditions, etc. Many centrifuge model tests have been carried out on the topic of ground improvement, which can be classified into two categories: the investigation of soil properties’ changes and the behavior of original ground during ground improvement work or the investigation of the behavior of improved ground. The Port and Airport Research Institute carried out many centrifuge model tests on research topics related to several ground improvement techniques over many years. In this report, several examples of centrifuge modelling carried out at the Institute regarding these two categories are briefly introduced.
Simulation of Soil Movement in Geotechnical Centrifuge Testing – Deep Excavations, Tunnelling, Deposit
D. König, O. Detert and T. Schanz
ABSTRACT: Foundation engineering works are mostly related to movement of soil masses. Excavation of construction pits and of tunnels, construction of embankments and dams, all these activities impose the take of, transport and deposit of more or less huge amount of soil masses. These processes of soil movement lead to change of stress, activation of shear resistance and deformation in the remaining or underlying soil. To control such effects special works like installation of retaining structures, soil stabilisation by nailing or injection, improvement of drainage conditions or others are carried out. These measures have to be designed taking into account the interaction with the surrounding soil and the construction process. Up to now not all of the relations between the different construction elements and soil reactions are fully understood. Independent on the progress in numerical modelling physical modelling is helpful to discover and analyse such interactive reactions. For this it is necessary to simulate soil movement in physical modelling. Especially in centrifuge modelling this is a challenge. Within this paper an overview is given of different methods to simulate soil movements in the geotechnical centrifuge and three examples on projects carried out in the Bochum Geotechnical Centrifuge ZI are described more in detail. The main topics are the excavation of construction pits, the excavation of tunnels and the deposit of soil masses.
Run-out of Sensitive Clay Debris: Significance of the Flow Behavior of Sensitive Clays
V. Thakur and D. Nigussie
ABSTRACT: Geohazards in the form of massive flow slides in sensitive clay deposits have been responsible for the loss of human lives and damage to nearby infrastructure. The run-out of sensitive clay debris involved in such flow slides is, among others, largely influenced by the remolded shear strength (cur) of the sensitive clays. The present work studied this factor using a small-scale model referred to as the run-out test. The results demonstrated that sensitive clay debris with cur < 0.3 kPa have a potential for a longer run-out, whereas a very short run-out was observed for the sensitive clay debris with cur >1 kPa. These observations were back-calculated using the three-dimensional numerical tool DAN3D.
Verification of the Generalized Scaling Law for Flat Layered Sand Deposit
T. Tobita, S. Escoffier, J. L. Chazelas and S. Iai
ABSTRACT: To verify the generalized scaling law, dynamic centrifuge tests under two different centrifugal accelerations of 25 g and 50 g are conducted. The model ground constitutes of a flat dry sand layer. With the scaling law, a prototype ground is scaled down to 1/100. A sinusoidal input acceleration of frequency 1.0 Hz, maximum amplitude 0.5 g, and duration 14 sec in prototype scale is applied to the model ground. Each model is exposed to the identical input motion sequentially 10 times. In total nine accelerometers are installed in the model. Surface settlements are measured by laser displacement transducers. Settlements at three different depths (300, 200 and 50 mm – model scale – from the surface) are measured by settlement gauges. Response acceleration and penetrometer resistance show good agreements in prototype scale. Measured settlements after the initial shake in prototype scale also show significant agreements between the two models when the intensity of shaking is nearly identical. As shaking continues discrepancy in settlement becomes large due to minor differences of input acceleration levels and random error associated with model constructions.
Performance of Rail Embankments Constructed with Coal Ash as a Structural Fill Material: Centrifuge Study
B.V.S. Viswanadham and V.K. Mathur
ABSTRACT: The objective of the present study is to understand the stability and deformation behavior of rail embankments constructed with coal ash as a structural fill material through centrifuge model tests. Two types of railway embankments were modeled: 1) Clay confined coal ash embankment with 1V:2H slope of 11 m height and 2) Geogrid reinforced coal ash embankment with 2V:1H slope of 4 m height using a large beam centrifuge facility available at IIT Bombay. Considering the nature of railway embankments and possibility of buildingup of ground water table due to rainfall, a seepage tank simulator was used to induce seepage into the rail embankment during centrifuge tests. After establishing steady-state seepage conditions, the crest of the embankment was subjected to an incremental static loading pressure distributed through a rigid strip footing up to 700 kPa or failure, whichever occurred first. Additionally, an option of provision of drainage at the mid-height of the railway embankment was also explored for clay-confined coal ash embankments. Based on the analysis and interpretation of centrifuge model test results, for a soil confined coal ash embankment with 1V:2H slope with a confinement layer of 1.5 m thickness in the top-half height and berms in the bottom-half zone was observed to sustain an ultimate load bearing pressure of 400 kPa. Geogrid reinforcement layers in a reinforced coal ash embankment with 2V:1H slope were observed to experience straining after applying a bearing pressure of 250 kPa in the top-half zone and indicating a need to provide high strength layers in top-half zone. Further, results of stability analysis of soil confined coal ash embankment models constructed with coal ash as a fill material were found to corroborate well
with physically observed centrifuge test results.
Field Scale Tests for Determination of Pullout Capacity of Suction Pile Anchors under Varying Loading Conditions
Vijaya Ravichandran, R. Ramesh, S. Muthukrishna Babu, G.A. Ramadass, M.V.Ramanamoorthy and M.A. Atmanand
ABSTRACT: Full scale tests have been conducted on suction pile anchors for testing the pullout behaviour under various loading conditions for mooring applications. Suction pile anchors with varying diameters and constant length to diameter ratios have been used in the tests. The tests have been carried out in the field within breakwaters where natural environmental factors like wind, lower waves and tidal influence exists. Comparison has been made between static pullout and dynamic loading on the suction pile. It is found that the pullout capacity of the suction pile anchors is influenced by pile geometry, angle of pullout and nature of pull (static/dynamic loading).
A Novel Mobile Information System for Risk Management of Adjacent Buildings in Urban Underground Construction
Hanh Quang Le and Bin-Chen Benson Hsiung
ABSTRACT: Adjacent structure, Risk Management, BIM, Mobile web service, Urban Underground
During the urban underground construction, control of behaviours and assessment of hazards to adjacent structures right at the sites can be extremely difficult owing to processing data from various types of monitored instruments corresponding to multiform of building structures. In this paper, a novel mobile web-based comprehensive information system, named MitiRisk, which is combined from building information model – BIM, mobile web service technology to be presented. In the proposed system, building information model is applied to visualize the current situation of monitoring building structures, whereas, mobile web service technology is used to enable effective necessary data exchange in real-time. Testing examples of the developed system to the O6 station’s excavation in Kaohsiung metro system in Taiwan and application scenarios in Metro line 1 (Ben Thanh – Suoi Tien) in Ho Chi Minh metro system in Vietnam, are presented to illustrate the improvements of safety management to adjacent structures in urban underground construction projects.
Comparison between Design Methods Applied to Segmental Tunnel Linings
N.A. Do, D. Dias, P.P. Oreste, I. Djeran-Maigre
ABSTRACT: Development of the underground construction system in urban areas in Vietnam, such as Hanoi capital and Ho Chi Minh city, plays an important role to improve the public infrastructures. As most of the tunnels driven in urban areas using mechanized tunnelling method, segmental linings will be utilized in this project. One of the most important aspects during the design of a segmental tunnel lining is to consider the effect of segmental joints on its overall behaviour. This paper has the aim to introduce comparative results of calculated internal forces obtained by using analytical analyses, that is, Einstein & Schwartz’s method, elastic equation method, and a two-dimensional numerical analysis, in which the effects of segmental joints have been taken into account. A cross-section of a twin bored tunnels of the Nhon – Hanoi Railway station section of the Hanoi pilot light metro has been used as a case studied.
KEYWORDS: Analytical method, Internal forces, Numerical method, Segmental lining, Tunnel
Challenging Construction Projects Related to Urban Tunnels
R. Katzenbach and S. Leppla
ABSTRACT: The growing size and population density of metropolitan areas and the along going traffic demands lead to the construction of large infrastructure projects. In many cases these infrastructure projects are close to sensitive properties. The construction of new underground structures and the deconstruction of existing structures often have a significant influence on existing (underground) structures. The experiences of two large projects from Spain and Germany will be presented in the paper. The first of the presented projects is the new tunnel of the Spanish high speed railway line under the city centre of Barcelona, Spain. The tunnel boring machine (TBM) with a diameter of 11.55 m passed next to two buildings that belong to the World Heritage Properties of the UNESCO. The second project is the deconstruction of an up to 14 storeys high building in Frankfurt am Main, Germany. Under the deconstructed building are an underground station and tunnels of the urban metro system. The uplift and deformation of the underground structures had to be limited to guarantee the serviceability of the sealing. The paper focuses on the extensive geotechnical and geodetic measurement programs that were installed regarding the observational method and the measurement results. The experiences made in the planning and construction phases of these complex projects are explained and for new inner urban projects recommendations are given. In order to reduce the subsidence risk, earth pressure balanced shield machines are a good solution in an urban environment in comparison to other tunnelling methods. Settlements are evoked by changes in the stress conditions or changes in pore water pressure. With an active support pressure of the face, of the gap between the shield and the surrounding soil and the gap behind the tail of the shield these changes can be reduced to a minimum. Nevertheless settlements or ground subsidence occur in every tunnel construction process. To characterise the settlement trough in width and depth over a tunnel section the volume loss factor Vl can be used. Vl describes the volume of the settlement trough to the theoretical tunnel volume.
Bulk Compression of Dredged Soils by Vacuum Consolidation Method Using Horizontal Drains
Hiroshi Shinsha and Takahiro Kumagai
ABSTRACT: Two landfill sites were constructed on shore to dispose of dredged soil, and dredged soil was reclaimed after the placement of horizontal drains. In this manner, bulk compression of the soil has been achieved by application of vacuum consolidation method. The horizontal drain was a plastic board drain (PBD) with a width of 100 mm, a thickness of 10 mm, and a length of 117 to 171 m. The PBDs were set at both the bottom and the intermediate height of the landfill sites with a horizontal spacing of 0.8 m, and were completely overlaid with the dredged soil. By alternately placing the drain material and disposing of dredged soil at two landfill sites and applying negative pressure continuously to the sedimentary soil, it was possible to deposit an amount of sedimentary soil that corresponds to about 1.1 times the disposable volume at the landfill sites. This paper outlines the implemented construction and presents various measurement results and a settlement analysis.
Mechanical Behaviour of Energy Piles in Dry Sand
A.M. Tang, A. Kalantidou, J.M. Pereira, G. Hassen, N. Yavari
ABSTRACT: In this study, for investigating the mechanical behaviour of energy pile, the behaviour of an axially loaded pile under thermal cycles was investigated using a physical model. After applying the axial load by dead weights on the pile’s head, the pile was heated from 25°C to 50°C and subsequently cooled to 25°C. Four tests (corresponding to four values of axial load) were performed and two temperature cycles were undertaken in each test. When low axial loads were applied, the heating induced heave and cooling induced settlement of the pile’s head. In the case of higher axial loads, the heave of the pile’s head, obtained during heating, was lower than the thermal expansion of the pile demonstrating the settlement of the pile’s toe.
Estimating Side Resistance of Bored Pile in Residual Soils
Mutiasani Dianmarti Kusuma and Eng-Choon Leong
ABSTRACT: Bored piles are extensively used as foundation in Singapore residual soils. However, traditional design of bored piles is based on properties of clays, sands, or rocks. In addition, bored piles are design to rely on base resistance In addition, bored piles are design to rely on base resistance (Qb) despite the fact that side resistance’s (Qs) contribution towards axial capacity is higher at the working load. Using instrumented pile load test results from Bukit Timah Granite and Jurong Formation residual soils, correlations for unit side resistance (fs) with SPT-N and soil properties were developed. The estimates of side resistance (Qs_est) from the developed correlations were compared with Qs_est from recommendations by other researchers which have been adopted in practice. Based on the comparison, the design of bored piles installed in Singapore residual soils can be optimized using the developed correlations.
Seismic Response of Geosynthetic Reinforced Earth Embankment by Centrifuge Shaking Table Tests
W.Y. Hung, J.H. Hwang, C.J. Lee
ABSTRACT: The advantages of reinforced earth structures are their flexibility and capability to absorb deformations due to poor foundation and seismic loadings. In this study, 7 centrifuge shaking table tests were performed to investigate the effect of reinforcement arrangement on seismic response of geosynthetic reinforced earth embankment. The test results show that the natural frequency of an 8 m-high GRE embankment is about 5.7Hz. The arrangement of reinforcement and the inclination of slope facing do not affect the natural frequency significantly. The amplification of acceleration increases with the increasing elevation and the increasing frequency of input motion. If the embankment has enough reinforcement strength, the reinforcement spacing and the inclination of slope facing would not affect the settlement significantly. Insufficient reinforcement strength would lead to internal instability failure and a large settlement. The external instability would occur for the embankment using too short reinforcement length.
KEYWORDS: Centrifuge shaking table test, geosynthetic reinforced earth embankment, natural frequency
