1g model tests of piled-raft foundation subjected to high-frequency vertical vibration loads

Abstract

The piled-raft foundation (PRF) has been used in high-speed railway in China. If the design and construction of the foundation is done without taking proper precautions, then the vibration loads induced by the high speed trains may cause excessive settlement of the foundation, significantly affecting the stability and safety of trains. To carefully examine the settlement mechanisms of PRFs constructed in different grounds subjected train loads, systematic 1 g model tests were conducted. The dynamic responses of PRFs in dry loose sand, medium dense sand, and saturated medium dense sand ground, subjected to different frequencies of sinusoidal vibration loads, were investigated. Additionally, reinforcement effect of cement-treated partial ground improvement (PGI) for dry loose sand ground, a commonly used countermeasure against settlement of PRF, was also investigated via model tests. It is found that the dynamic loading frequency affected the settlement of PRF, and the pattern of PGI reinforced at different depths of pile also significantly affected the settlement. The model test also showed that load-sharing ratio between pile and raft also changed significantly during vibration loading, implying that extensive precaution should be taken in design and construction of PRFs for high-speed railway constructed in soft ground.