Numerical Analyses of a Piled Raft Foundation With Grid-Form Dmws Under Large-Scale Earthquakes

Abstract eng:
The seismic performance of a piled raft foundation with grid-form cement deep mixing walls (DMWs) under a large earthquake load is evaluated numerically. A base-isolated building located in Tokyo is modeled as a detailed threedimensional finite element ground–structure interaction model. An elasto–plastic multi-surface model directly using the G- and h- characteristics as the input parameters is used for the soil, and a nonlinear model with tensile and shear criteria is applied to the stabilized soil. In this study, the model is first validated by comparing it with the observation records from the 2011 off the Pacific Coast of Tohoku Earthquake which was categorized as a medium earthquake at this site. And then a seismic response analysis using a large earthquake that is officially notified in Japanese design codes is conducted. According to the analysis, the maximum bending moment of the piles in the case with the grid-form DMWs is within the allowable criterion of the NM relation of the steel pipe–concrete composite pile, while that in the case without DMWs is markedly large and beyond the ultimate criterion. Consequently, it is found that the grid-form DMWs are very effective at reducing the sectional force of the piles to an acceptable level, even if the induced stress in the DMWs partially reaches its tensile strength during a large earthquake.

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