Sectional forces on piles during earthquakes are affected not only by the inertial force of the structure but also by ground deformation. In this study, a series of shaking table and static lateral loading tests on pile groups and piled raft foundations were conducted in a centrifuge to estimate the influence of ground deformation on the bending moment in the piles. The results, including the effect of the ground deformation, were compared to those of the static lateral loading tests without ground deformation. Most of the inertial force was transferred to the subsoil through the raft by friction on the piled raft and the bending moments in the piles in the piled raft caused by ground deformation were almost the same as those in the pile group.

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A FE – BE coupling technique is used in the present study for prediction of elastic settlement of rectangular piled raft foundations. The raft is idealised as a thick plate freely resting on soil medium, which is idealised as a semi-infinite, isotropic and homogeneous elastic half -space. The plate and the half- space are two separate models in unilateral and frictional contact at the interface. Pile is idealised as a spring of equivalent stiffness, obtained from simplified approach based on elastic theory assuming it to be a shaft in the half-space. Boundary element method is employed to determine the soil stiffness matrix by inverting the soil flexibility matrix, using Mindlin’s solution for a point load in half-space as a fundamental solution. Finite element method is employed to determine the raft stiffness matrix based on Mindlin’s plate bending theory, which allows transverse shear deformation. Transformation of the boundary element matrices are carried out to make it compatible for coupling with plate stiffness matrix obtained from finite element method. Combined stiffness matrix of the soil-pile-raft system is obtained by summing up the stiffness of the soil-raft system and the stiffness contribution of the piles at selected locations. A computer programme is developed, based on the procedure describe above, in which discretisation is automatic and requires very nominal data input. Effect of pile parameter on settlement of a piled raft system subjected to uniformly distributed load is studied for different number and configuration of piles to demonstrate the efficacy of piled raft system in reducing settlement.

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This paper presents settlement and load sharing behavior of a piled raft supporting a low-rise building subjected to strong seismic motion. On March 11, 2011, the 2011 off the Pacific coast of Tohoku Earthquake struck the building site. Based on the field monitoring results of the piled raft before and after the earthquake, it was found that the foundation settlement near the raft center was increased by 4.1 mm to 24.8 mm while the ratio of the load carried by the piles to the effective structure load was decreased slightly. A mechanism of the increase in settlement of the piled raft subjected to the strong seismic motion is discussed. Using a hysteretic load-unload-settlement curve derived from a rapid load pile testing and a settlement ratio obtained from the results of the pile testing and the field monitoring, the increment in settlement of the piled raft was estimated to be 3.8 mm which roughly agreed with the measured value.

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Disconnected piled raft (DPR) or non-connected piled raft is a foundation approach with highly growing interest over the past few decades. This technique, where the raft is separated from the piles by interposing a load transfer platform (LTP), allows engineers to apply a much lower safety factor against structural failure compared to the piled foundations in which piles are structurally connected to the raft. Also possible damage to structural connections is no longer a design issue, and the horizontal loads can be effectively transmitted through the mobilized frictional force along the soil-raft interface. This paper aims to study the behavior and performance of DPR foundation under vertical loading through a parametric study. In this study, three dimensional finite element method (3D FEM) via Plaxis 3D has been employed to model the complex interactions of this DPR taken into account the load transfer in the LTP and along the pile. The analysis consists of the investigation of the effect of dominant parameters such as the area replacement ratio (pile area to mesh soil area), soil and pile stiffness, and the thickness and strength parameters of LTP. Edge effect resulting from the friction between reinforced soil and non-reinforced soil is also investigated. The results from parametric study have shed some light on design optimization.

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During the last few decades, the quick growth of cities all over the world led to a rapid increase in the number and height of high-rise and super high-rise buildings, even in unfavourable subsoil conditions. Piled raft foundation concept, in which piles only for reducing the settlement, not for carrying the whole load from the superstructure, has been successfully applied for many projects. This design philosophy has also been increasingly applied for high-rise buildings. In this paper the result from the Author’s experimental study, which strongly supports the concept of settlement-reducers are reviewed. The experimental results are surprisingly in good agreement with case histories many years later. Applications of the proposed simplified design method in combination with FEM in design of piled-raft foundations for high-rises are also discussed.

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Load and settlement behaviors of a numerical pile-raft foundation in soft soils after the consolidation are presented in this paper. Modified Cam Clay (MCC) model was adopted to model the soil behaviors. Three dimensional FEM analysis based on MIDAS-GTS program was conducted in the study. The influences of pile-to pile spacing distance and pile length as well as soil model parameters were monitored. It generally finds that the trend of the load distribution and settlements of piles and raft are dependent of these effects. A post consolidation analysis for a pile-raft foundation under the loads could be suggested for the long-term condition of the foundation.

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Tunneling under roadway/railroad in a busy urban area is not an easy work due to a hostile environment involving weak ground and a shallow embedded condition and resulting in a great possibility of tunnel face stability problems. Divided Shield Method (DSM) is one of techniques to reduce the instability of the tunnel face using divided steel plates as a shield for tunneling. This study investigated the effectiveness of layers of the horizontal pipe grouting at the face of DSM tunneling on the stability and construction speed. The investigation was undertaken by the test chamber and its numerical verification. Surface deflection of the chamber fill and the stability of the tunnel face were measured with the excavation sequence. Numerical analyses of the chamber test were conducted to predict further behaviors of DSM tunneling. The results of the study show that DSM tunneling reinforced by horizontal pipe grouting reduced the ground movement and construction time, and enhanced the stability of the tunnel face significantly. Using the test and analysis results, the potential development of a new method that can reduce the construction period was discussed in detail.

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