Reduction of Liquefaction-Induced Kinematic Pile Loading By Means of In-Ground Ringwall

Abstract eng:
This paper presents an approach to reducing liquefaction-induced kinematic loading on piles by means of an in-ground ringwall made of overlapping jet grout columns. A vulnerability assessment using Dynamic Soil-Structure Interaction (DSSI) analysis of the pile foundation of an existing liquefied petroleum gas (LPG) spherical storage tank has identified that the piles capacity will be exceeded during a design earthquake. Liquefaction assessment indicated that several soil layers may liquefy and create non-liquefied ‘crusts’ that impose additional lateral deformation along the length of the pile. The precast pre-stressed concrete piles had relatively low lateral capacity and were prone to bending failure during earthquake shaking. A retrofit study was performed to assess the effectiveness of an in-ground wall concept in minimizing the kinematic loads on the piles. The concept was to construct overlapping jet grout columns that form a ringwall that would deflect the kinematic loading of the non-liquefied ‘crusts’, shielding the brittle piles during earthquake shaking. To help select efficient ringwall configurations, several pushover analyses were performed varying the ringwall thickness and depth. Finally, the optimized ringwall configurations were incorporated into the full DSSI model and subjected to two orthogonal horizontal acceleration time histories. Results indicated that the in-ground ringwall greatly reduced the kinematic loading on the piles, and hence piles that once failed now perform within capacity. The DSSI analyses provided ‘proof of concept’ that shows inground walls reduce kinematic loading and can be used to retrofit the existing foundations.

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