Seismic response of mid-rise buildings on shallow and end-bearing pile foundations in soft soil

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Journal Article
Soils and Foundations, 2014, 54 (3), pp. 345 - 363
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The seismic behaviour of structures built on soft soil is influenced by the soil properties, and the response is significantly different from the fixed-base condition owing to the interaction between the ground and the structure. In this study, in order to investigate the influence of the foundation type on the response of structures, considering soil-structure interaction, a series of experimental shaking table tests has been conducted for three different cases, namely, (i) a fixed-base structure representing the situation excluding the soil-structure interaction; (ii) a structure supported by a shallow foundation on soft soil; and (iii) a structure supported by an end-bearing pile foundation in soft soil. A laminar soil container has been designed and constructed to simulate the free-field soil response by minimising the boundary effects. Simulating the superstructure as a multi-storey frame during the shaking table tests makes the experimental data unique. A fully nonlinear three-dimensional numerical model employing FLAC3D has been adopted to perform a time history analysis and to simulate the performance of the structure considering the seismic soil-structure interaction. Hysteretic damping of the soil is implemented to represent the variation in the shear modulus reduction factor and the damping ratio of the soil with cyclic shear strain. Free-field boundary conditions have been assigned to the numerical model and appropriate interface elements, capable of modelling sliding and separation between the pile and the soil elements, is considered. A comparison of the numerical predictions and the experimental data shows a good agreement confirming the reliability of the numerical model. Both experimental and numerical results indicate that soil-structure interaction amplifies the lateral deflections and inter-storey drifts of structures supported by end-bearing pile foundations in comparison to fixed-base structures. However, pile foundations contribute more to the reduction in lateral displacements than shallow foundations due to the reduced rocking components. Consequently, the choice of foundation type is dominant and should be included when investigating the influence of SSI on the response of superstructures during shaking excitations, which is significantly important in the performance-based design of structures. © 2014 The Japanese Geotechnical Society. Production and hosting by Elsevier B.V. All rights reserved.
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