ESTIMATING LIQUEFACTION RESISTANCE IMPROVEMENT DUE TO STONE COLUMNS FROM QUALITY CONTROL TESTS

Abstract

Stone columns are often used in cohesionless soils to decrease their liquefaction susceptibility; however, methods of predicting how much liquefaction resistance increases due to stone columnsgreatly vary. All these methods depend on knowing the stone column stiffness but the quality control tests in the field do not lead to measuring actual column stiffness directly, especially the popular plate load tests on a single stone column. A series of axisymmetric numerical simulations of stone column compression investigate the relationship between the actual stone column stiffness and that interpreted from test results. The paper also presents the results of plane-strain numerical models simulating a reference earthquake acting on a unit cell improved by a stone column. The dynamic analysis assesses the change in liquefaction resistance with increasing column stiffness and friction angle. The analysis results show that the PM4Sand dynamic constitutive model is more suitable than the UBC3D-PLM model in capturing the sensitivity of liquefaction resistance to soil improvement and stone column stiffness. The degrees of improvement in liquefaction resistance predicted in the study agree well with what the theories based on combined shear and flexural stone column deformation mechanisms predict. Finally, the paper presents design curves to get a quick estimate of the degree of improvement in liquefaction resistance from plate load test results.