Simplified models for soil-nail lateral interaction
(2000) Tan, S.A.; Luo, S.Q.; Yong, K.Y.; CIVIL ENGINEERING
A series of simplified failure modes has been used in this paper to describe the behaviour of soil-nail lateral interaction. The criteria for determination of the possible failure modes for a soil-nail structure are set out on the basis of the relative stiffness and strengths of the soil and nail and the local relative lateral displacement across the shear zone. This local relative displacement is produced along a potential sliding surface of the reinforced soil-nail retaining structure. Expressions for calculation of soil-nail lateral resistance have been derived for each potential failure mode. It is found that soil-nail lateral resistance is dependent not only on the relative stiffness and yield strengths of the soil and nail but also on the local relative lateral displacement across the shear zone. Good agreement among the results of numerical simulation of soil-nail lateral performance, published experimental data and theoretical predictions have been demonstrated, to support the validity of the proposed approach for estimating soil-nail lateral resistance capacity in soil-nailing design.
Time-dependent deformation of anchored excavation in soft clay
(1991) Lee, S.I.; Parnploy, U.; Yong, K.Y.; Lee, F.H.; CIVIL ENGINEERING
Excessive movement of excavation support system may result in construction delays and damages to underground services, roads and near-by buildings. It was observed in the field that after excavation, the support system continue to deform even though there was no further excavation. In this paper, the time-dependent deformation of anchored excavation in soft clay was analysed by using a fully coupled consolidation analysis with elasto-plastic soil model. Computed deformation of the excavation support system was found to be in close agreement with field performance of an anchored sheet pile wall which was carefully monitored during excavation.
Three-dimensional numerical simulation of tunnel advancement on adjacent pile foundation
(2005) Pang, C.H.; Yong, K.Y.; Chow, Y.K.; CIVIL ENGINEERING
In this paper, the development of a three-dimensional finite element model to back-analyse a case history on the response of pile foundation subjected to shield tunnelling is described. The case history is from the construction of the MRT North-East Line Contract 704 in Singapore. The FE model was created to back-analyse the behaviour of one of the instrumented pile group at Pier 20 where the full shield tunnelling process, including the application of face pressure, shield tunnel advancement, over-cutting, tail void closure and installation of lining was simulated. The effect of single tunnel advancement was simulated and discussed. Good agreement between the results from analysis and measured data was obtained which validated the FE model. © 2005 Taylor & Francis Group.
A new finite element model for pile-soil interaction
(2004) Liu, K.X.; Lee, F.H.; Yong, K.Y.; CIVIL ENGINEERING
This paper describes the formulation and validation of a new finite element model for 3-D analysis of pile-soil interaction problems. The proposed element is constructed by wrapping 4 slip elements around a 2-nodes flexural element. The 4 slip elements are to model the interface between soil and pile and the 2-node flexural element simulates the pile segment. This element will lead to an ease of use in the 3D numerical analysis of soil-pile interaction problems with slip elements being built in one element and a significant reduction of numbers of system Degree of Freedom comparing to the conventional way of modelling pile with 20-noded brick elements. The element stiffness formulation is based on the weak formulation of virtual work principle with the internal equilibrium between pile and soil being governed by Euler's beam theory in lateral reaction. The FEM program using the proposed model was developed and verified and validated with analytical solutions and a simple case study.
The response of pile foundations subjected to shield tunnelling
(2006) Pang, C.H.; Yong, K.Y.; Chow, Y.K.; Wang, J.; CIVIL ENGINEERING
This paper presents a unique case history in Singapore on the study of the effects of shield tunnelling on the adjacent pile foundations. As part of the construction of the MRT North East Line contract 704, a viaduct bridge was planned in conjunction with the tunnel advancement. The bridge which consists of 2 abutments and 39 piers was constructed in parallel alignment with the new twin tunnels configuration. The piers were supported by groups of four to six 1.2 m diameter bored piles. Along the alignment, 6.5 m diameter tunnels were located very closely, i.e. 1.6 m clear distance, to the pile foundation. As part of the monitoring requirement, an instrumentation programme was implemented at six piers. A total of twelve piles were installed with strain gauges at various levels of foundations to monitor the piles'response during tunnelling. The data was then linked to settlement markers installed in the vicinity of the piles. The results show that the piles were subjected to large dragload particularly when higher volume loss was observed. Bending moments developed in piles were found to be much higher in the transverse direction (bending perpendicular) than in the longitudinal direction (bending parallel to tunnel alignment). © 2006 Taylor & Francis Group.
Ground improvement works in South-East Asia.
(1985) Lee, S.L.; Ramaswamy, S.D.; Karunaratne, G.P.; Lo, K.W.; Yong, K.Y.; Moh, Z.-C.; CIVIL ENGINEERING
Bangkok, Jakarta, Penang and Singapore are some of the major urban centres where soft ground conditions pose numerous geotechnical problems. Work in these areas of ground improvement has only recently taken on significant proportions in this region, in parallel with the present upsurge in variety and scope of construction more often requiring specialist services. Some methods such as soil nailing and geotextiles for soil reinforcement have yet to attain the degrees of implementation and acceptance of ground improvement techniques like deep compaction and the speeding up of consolidation, hence the corresponding lack of publication on their application in projects. -from Authors
A variational approach for the analysis of rectangular rafts on an elastic half-space
(1999) Shen, W.Y.; Chow, Y.K.; Yong, K.Y.; CIVIL ENGINEERING
A variational approach for the analysis of rectangular rafts on an elastic half-space under vertical loading is presented. The deflected shape of a raft is represented by a function with a set of undetermined constants. The response of the raft is determined by the use of the principle of minimum potential energy. The results based on the present method compare well with available published solutions.
Practical method for settlement analysis of pile groups
(2000-10) Shen, W.Y.; Chow, Y.K.; Yong, K.Y.; CIVIL ENGINEERING
This paper presents a practical method that can be used to evaluate the settlement of pile groups. This method is developed based on variational solutions for pile groups embedded in soil modeled using a load-transfer curve model and elastic half-space model. Using this practical method, the settlement of pile groups can be estimated quickly without recourse to complex computer programs based on numerical models, resulting in savings in time and cost. The solutions obtained using this approach are in good agreement with rigorous variational solutions and are also in reasonable agreement with field measurements.
Properties of Singapore marine clays improved by cement mixing
(2002-12) Tan, T.-S.; Goh, T.-L.; Yong, K.-Y.; CIVIL ENGINEERING
Stabilization of soft ground by the deep cement mixing (DCM) method has become an increasingly popular method to improve stability in an excavation in soft clay and to limit movement in adjacent sub-structures. The desired increase in strength and stiffness to fulfil the intended functions can be achieved provided that the right mix proportion is adopted. To proceed with this kind of soil improvement, prediction of the strength and stiffness of the improved soil is necessary. Due to a short history of the DCM method in Singapore, there is limited data on the improved properties of local clays. This study is conducted to bridge that gap and also extends its usefulness to clays elsewhere. In the paper, the influences of three main constituents of the mixture, namely clay, water, and cement on the strength development of Singapore marine clays improved by cement mixing are investigated. Based on the experimental results, it is shown that a convenient normalization can produce a consistent pattern for evaluation of improved strength of clays from different parts of Singapore. This normalization is also shown to work for one Japanese clay. Correlations between strength and stiffness of the improved clay are also obtained. Lastly, it is shown that for a cement mixed clay there is a continual increase in strength and stiffness with time. This will help to reduce ground movement, and it will also increase the bending moment in the retaining wall. Both aspects must be considered in a design.
Determination of consolidation properties for very soft clay
(1988-12) Tan, Siew-Ann; Tan, Thiam-Soon; Ting, Lai Choon; Yong, Kwet-Yew; Karunaratne, G.-P.; Lee, Seng-Lip; CIVIL ENGINEERING
A finite strain consolidation test with a constant surcharge to determine the compressibility (e-$odelta′) and permeability (e-k) relationships of very soft clay is proposed. The method uses Gamma-rays and pore pressure transducers to measure density and pore pressure profiles, respectively, at various times of the test without hindering the consolidation process. The constant surcharge applied accentuates the changes in density and pore pressure profiles enabling them to be measured reliably. These profiles are then used to determine the compressibility and permeability of the soft clay. A test is carried out to extract these properties, which are used in a finite strain consolidation theory to predict the settlement, void ratio, and pore-pressure distributions of other tests done under different initial and boundary conditions. The predictions are found to agree well with the experimental data, thus suggesting that the properties determined are accurate.

Kwet Yew Yong

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