Application research of sand well immersion test in collapsibility evaluation of loess tunnel foundations

It is difficult to accurately evaluate the collapsible deformation of the deep loess strata under loess tunnels by using laboratory compression test or field pit immersion test. In this paper, it is proposed to carry out sand well immersion test to measure and evaluate the collapsibility of loess tunnel foundations. Comparisons among the results of sand well immersion test, field pit immersion test and laboratory test were performed, and the reasonability and reliability of sand well immersion test used to evaluate the collapsible deformation of loess tunnel foundations were demonstrated. The results indicate that the collapsible deformation of soil columns around the sand wall could be effectively released under the immersion condition of the sand well test, and that the deeper the sand well is buried, the more the collapsible deformation of the strata under the bottom of the well develops completely, which shows that the sand well immersion test is more applicable for measuring the collapsible deformation of loess strata with a large buried depth. The sand well immersion test can better simulate the hydraulic condition of collapse deformation of the strata under the tunnel foundations, and the test method can be applied conveniently along the tunnel in loess plateau region due to low requirement of site conditions, less water, short cycle and low cost. Finally, some improvements were put forward to solve the defects of sand well immersion test at present. © 2019, Science Press. All right reserved.