Abstract: To determine the earth pressure at rest of light weight soil mixed with expandable polystyrene(EPS) particles behind a retaining wall, the model tests are conducted for remolded soil and light weight soil respectively. The distribution laws of earth pressure at rest, coefficient of earth pressure at rest and vertical settlement deformation of the filler behind retaining wall are explored under loading and unloading processes, and the mechanisms of pressure reduction and settlement deformation of light weight soil are clarified. The results show that the vertical earth pressure and lateral earth pressure of remolded soil and light weight soil increase linearly with the increasing of filling depth before loading and unloading, and the relative errors between theoretical values and measured values for vertical earth pressure and lateral earth pressure are no more than 26.35%. The effect of load on vertical earth pressure and lateral earth pressure decreases with the increase of filling depth for remolded soil. After curing, light weight soil has self-supporting property, thus the influencing depth of load on light weight soil is limited. In this test, the load influencing area depth of light weight soil is about 50% of the wall height. In the process of loading and unloading, when the filling depth is less than 50% of the wall height, the vertical earth pressures and lateral earth pressures of light weight soil increase or decrease obviously with the gradual load increasing or decreasing. When the filling depth is greater than 50% of the wall height, the vertical earth pressures and lateral earth pressures gradually converge with the gradual load increasing or decreasing, but the change range is smaller. The measured coefficients of earth pressure at rest of remolded soil and light weight soil are non-linear distribution behind the retaining wall, which are in the range of 0.27?0.74 and 0.33?0.44, respectively. The theoretical values of the coefficient of earth pressure at rest calculated by Jaky formula are basically larger than the measured values, but the difference is smaller. The vertical settlement deformation of remolded soil decreases with the increasing of filling depth, which is approximately 0?21.5 mm. The vertical settlement of light weight soil after curing has no obvious change under load, which is approximately 0?2.8 mm. Compared with remolded soil, light weight soil after curing has good buffering and self-supporting capacity, which can more effectively absorb and disperse the vertical pressure, due to the buffering effect of EPS particles and the solidification effect of cement. Light weight soil can greatly reduce the earth pressure at rest, the coefficient of earth pressure at rest and vertical settlement deformation, and meet the requirements of filling load reduction in retaining wall engineering.

Key words: light weight soil, retaining wall, earth pressure at rest, coefficient of earth pressure at rest, model test