3d Dynamic Impedances of Surface Footings on Liquefiable Soil: Equivalent Linear Approach


Abstract eng:
Recent experimental and theoretical studies suggest that deep foundations may be avoided in a liquefaction regime, in the presence of a non-liquefiable layer on top of the liquefiable of adequate thickness and shear strength, which can restrain the accumulation of excessive seismic settlements and prevent post-shaking bearing capacity failure. This evidence has given rise to attempts for a complete design approach for the performance-based design of shallow foundations on liquefiable soils [1 – 3]. The design is based on the idea of a permeable crust (natural or artificial) which needs not extend over the whole depth of the liquefiable sand in order to take advantage of the observed benefits of settlement reduction [4, 5] at a reduced thickness and width. Within the above context the need arises to investigate the dynamic response of shallow foundations on liquefiable soils. The focus of the present study is upon the influence of liquefaction on the dynamic stiffness and damping (“impedance” functions) of rigid square footings resting on a multilayer soil profile involving a liquefiable layer, under external harmonic loading. To this end, a three-layer soil profile consisting of a surface clayey crust over a loose liquefiable sandy layer followed by a stiff impervious base stratum, are considered. The dynamic impedance of a rigid square footing is investigated parametrically using computer software CONAN [6], which is based on wave propagation in cones. A limited number of rigorous 3D numerical analyses with boundary elements [7] was also performed to check the accuracy of the cone models. Vertical, horizontal and rocking oscillations are considered. The results show that for common soil, foundation and seismic excitation conditions, liquefaction in the foundation soil leads to significant degradation of the dynamic spring coefficients and increase of the associated damping coefficients.

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Conference Title:
Conference Title:
16th World Conference on Earthquake Engineering
Conference Venue:
Santiago (CL)
Conference Dates:
2017-01-09 / 2017-01-13
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 Record created 2017-01-18, last modified 2017-01-18


Original version of the author's contribution as presented on USB, paper 2126.:
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