Parameter identification of soil properties in shaking table test on liquefiable soil-high-rise buildings system

Based on the shaking table tests on liquefiable soil-high-rise buildings interaction system, the site liquefaction mechanism and dynamic characteristics of liquefiable soil during earthquake excitation were analyzed by using parameter identification technique to study the acceleration and water pore pressure records. The time-history curves of cyclic shear stress and shear strain in the soils were evaluated from the acceleration records in the soil by one-dimensional shear beam model. These time-history curves were used to estimate variation in dynamic shear modulus of soil and material damping characteristics with shear strain amplitude. Shear wave velocity, effective stress path and shear strain of pile and soil were discussed further. The analysis result shows that: Under the stronger earthquake excitation, the soil stiffness increases with the increasing depth; the stress-strain loops are rounded and show larger hysteretic damping characteristics for large earthquake excitation; the ratio of pore water pressure to vertical effective consolidation pressure goes up obviously; the increasing pore water pressure has influence on shear wave of soil; soil stiffness and shear strength both decrease with the increase in pore water pressure. Soil stiffness calculated from measured accelerations is consistent with that obtained through independent laboratory tests; but the material damping calculated from measured accelerations is much larger than that measured in laboratory tests, which is smaller than the equivalent damping associated with hysteretic damping. The shear strains in the soils inside and outside the pile group were found to be compatible. However, the amplitude of the shear strain outside the pile group is larger than that inside the pile group. The parameter identification technique of soil properties is useful for studying liquefaction field and practical seismic design of structure in liquefaction field.