SHO SHIRAHATA

Development of new triaxial liquefaction test considering in-situ testing

HIROHUMI TOYOTA

This study develops a new triaxial liquefaction testing method that considers in-situ liquefaction test, referred to as cyclic pressure meter (CPM) test. Axial cyclic loading is applied under constant lateral pressure in the conventional triaxial liquefaction test. However, in CPM test, lateral cyclic loading is applied in a borehole under constant vertical overburden pressure. Therefore, a new triaxial testing, which can simulate the close stress conditions with CPM test, was developed in the study.
The specific testing methods are follows: 1. Cyclic loading begins under isotropic stress condition because this condition has been used in the conventional triaxial liquefaction test. 2. As the cyclic loading, the lateral stress is first increased and then decreased at a constant rate up to the initial isotropic stress. This process is continued cyclically until liquefaction occurs. 3. This lateral cyclic loading is conducted under a constant axial stress condition. Suitable loading rate, for which the control conditions above mentioned are satisfied, was investigated.
As an example, Toyoura sand specimens with a relative density of 40% were prepared and saturated. A newly developed cyclic loading was applied under undrained conditions. Liquefaction was defined at a residual axial strain of 5%,
The newly developed control was confirmed to work properly from the results. Furthermore, liquefaction strength obtained from the new test was much smaller than that from the conventional triaxial liquefaction test. As a next step, the study should clarify its mechanism why large difference appeared between two liquefaction testing methods.