Dynamic Centrifuge Tests of Soft Clay Reinforced by Soil-Cement Grids

A pair of large centrifuge tests was conducted to evaluate the effect of soil-cement grid reinforcement on the seismic response of a deep soft soil profile. The soil profile consisted of a 23-m-thick layer of lightly overconsolidated clay, underlain and overlain by thin layers of dense sand. Each centrifuge model had two separate zones for a total of four different configurations: a zone without reinforcement, a zone with an embedded soil-cement grid that penetrated the lower dense sand layer and had a unit cell area replacement ratio of Ar=24%, a zone with an embedded grid with Ar=33%, and a zone with a floating grid in the upper half of the clay layer with Ar=33%. Models were subjected to 13 shaking events with peak base accelerations ranging from 0.005 to 0.31g. This paper examines the effect of the soil-cement grids on the global responses of the soil profiles, and the internal interaction between soil-cement grids and their enclosed soils. Nonlinearities in the dynamic responses and interaction mechanisms are examined using (1)time series of accelerations, shaking-induced excess pore-water pressures, and postshaking reconsolidation settlements; (2)response spectra and spectral ratios; (3)back-calculated composite stress-strain responses; (4)analyses of internal stress distributions between the grids and enclosed soils; and (5)dynamic crack detections and posttest crack mapping in the soil-cement grids. The results provide insights on the dynamic performance of soil-cement grids and an archived dataset for evaluating design procedures and numerical analysis methods.