The aim of this study is to reveal a useful soil stabilization method to increase lateral resistance of existing coupled piles. The authors conducted three kinds of lateral loading tests of coupled piles; centrifuge model test, large-scale model test and X-ray CT scanning model test. The authors discuss how a pair of coupled piles resists against lateral loading compared with a single tilted pile. The experimental results show the ground intermediating between two tilted piles composing a pair of coupled piles exerts lower ground reaction compared with the ground surrounding a single tilted pile.
The paper describes a method to stabilize the intermediate ground of coupled piles using cement treating technique. The paper also describes experimental results of the model tests to evaluate effects of several conditions in terms of depth and strength of cement-treated soil on the lateral resistance of coupled piles for which the intermediate ground is stabilized with its mechanism of increasing lateral resistance. Based on the experimental results, the authors introduce how to determine the specific of soil stabilization of intermediate soil.

Key Words: Coupled piles, lateral resistance, cement-treating method, horizontal loading test, X-ray CT scanning