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E. Y. N. Oh
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THE APPLICATION OF NORMALITY RULE AND ENERGY BALANCE EQUATIONS FOR NORMALLY CONSOLIDATED CLAYS A. S. Balasubramaniam; E. Y. N. Oh; M. Bolton
Lowland Technology International Vol 7 No 1, June (2005)
Publisher : International Association of Lowland Technology

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Abstract

In this paper, it is reiterated that the Roscoe and Poorooshasb (1963) formulation of the stress strain behaviour of normally consolidated clays is indeed in a more generalized form which is easily amenable to incorporate deformations under various degrees of drainage and can be extended to include cyclic loading and time effects beyond the primary phase of deformation. Also, the formulation can be used for stress states below the state boundary surface to include lightly overconsolidated and heavily overconsolidated clays. Particularly, it is shown here that Cam Clay model of Roscoe et al. (1963) and Modified Cam Clay model of Roscoe and Burland (1968) as based on energy balance equations and the normality concept can be considered as the special cases of the original formulation of Roscoe and Poorooshasb (1963). In order to achieve this, all theories are presented in similar mathematical forms, adopting the same formulation of Roscoe and Poorooshasb (1963). Modified Cam Clay Model of Roscoe and Burland, and the Roscoe and Poorooshasb theory made identical predictions of the shape of the state boundary surface, the pore pressure development during undrained behaviour, and the volumetric strain in the drained tests for all types of applied stress paths. Also, Modified Cam Clay model was only successful in predicting the shear strains along radial stress paths. For non-radial stress paths, Modified Cam Clay model needed an additional set of constant deviator stress yield loci, and when such a set was incorporated, the prediction from Modified Cam Clay model was the same as the original prediction of Roscoe and Poorooshasb (1963).
A MORE FUNDAMENTAL APPROACH TO PREDICT PORE PRESSURE FOR SOFT CLAY A. S. Balasubramaniam; E. Y. N. Oh; C. J. Lee; S. Handali; T. H. Seah
Lowland Technology International Vol 9 No 1, June (2007)
Publisher : International Association of Lowland Technology

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Skempton’s (1954) pore pressure coefficient A provides a pragmatic attempt at determining pore pressures during undrained shear, and to use these in settlement computations and stability analysis of embankments in soft clays. Also, the Critical state concept offers a means of acquiring the undrained stress path in normally consolidated clays through using a volumetric yield locus derived from a simple energy balance equation. However, to date there is no novel method by which the undrained stress paths of lightly over-consolidated and heavily overconsolidated clays can be predicted by using fundamental concepts. Based on the work of Handali (1986), Balasubramaniam et al. (1989) presented an alternative pore pressure coefficient that was more generalised than the Skempton’s coefficient. However, Pender (1978) proposed a set of parabolas to describe the undrained stress paths of overconsolidated clays, and Lee (1995) considered elliptic paths to be more in agreement with the experimental observations. In this paper, observed and predicted undrained stress paths both under compression and extension, and also from isotropic and K0 pre-shear consolidation states will be presented. Such expressions can then be readily used in computer softwares for stability analysis and settlement computations.
BORED AND DRIVEN PILE TESTING IN BANGKOK SUB-SOILS A. S. Balasubramaniam; E. Y. N. Oh; N. Phienwej
Lowland Technology International Vol 11 No 1, June (2009)
Publisher : International Association of Lowland Technology

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As a necessity to support an increasing magnitude of loads from tall buildings and long span bridges, the piling practice in the Bangkok Plain has moved several phases from driven pre-cast reinforced and pre-stressed concrete piles of smaller cross sections to spun piles and large diameter bored piles. The Chao Phraya plain in which the Bangkok city is located is low-lying and consists of a broad basin filled with sedimentary soils which form alternate layers of clay, sand, and clay. The upper clay layer is soft and highly compressible followed by a stiff clay layer extending to about 20 m or so and then followed by a layer of sand. Driven piles are normally taken down to this upper sand layer. However when the demand for a higher capacity arise, these piles cannot be extended in length due to construction problems and as such bored piles are needed to be taken down to as deep as 50 to 60 m. Below the upper clay layer there are eight interconnected aquifers from which ground water is pumped from deep wells. Thus in the design of piled foundations aspects such as the negative skin friction due to pile driving as well as deep well pumping are also needed to be considered. Some of the experiences gained over a period of 30 years in the study of piled foundations in the Bangkok Plain are briefly presented in this paper.
Co-Authors A. S. Balasubramaniam C. J. Lee M. Bolton N. Phienwej S. Handali T. H. Seah