Abstract
The authors studied on the effectiveness of two kinds of countermeasures against liquefaction, sand compaction piles and gravel drain piles, under Level 2 earthquake motion. In the current design of the sand compaction piles, the diameter and interval of sand piles are evaluated based on the critical density or SPT N-value of the ground. In this procedure, several items have not been considered. Among them, effect of increase of horizontal pressure due to the installation of sand piles were studied by conducting model tests and laboratory tests. Test results showed that liquefaction strength can be evaluated as about 1.2 to 1.4 times of the strength estimated by current design method, if the effect of K0 is considered. Effects of other factors were also studied by tests and analyses. In the gravel drain piles, effect of recover of shear modulus due to drainage on the settlement of structures in liquefied ground, was studied by conducting seismic response analyses. Analyzed results showed that the settlement of the structure can be decreased by installing drain piles, though liquefaction occurs under Level 2 earthquake motion.
