Experimental study on rebound and recompression deformation characteristics of different soils

For deep and large foundations, the soil below the foundation is often in a compensated or overcompensated state after the structure is completed. At this time, the proportion of recompression settlement to the total settlement is more significant. Attention should be paid to calculating the rebound deformation and recompression deformation of foundation pit excavation. In this work, the silty clay, clay, and silt in the Binhai New Area of Tianjin were studied. Oedometer tests were carried out on original and remolded samples to investigate the compressibility of different soil samples under unloading/reloading (the minimum unloading pressure ( P min ) was set to 50, 100, 200, and 400 kPa, and the maximum preloading pressure ( P max ) was kept at 400, 800, 1200, and 1600 kPa, respectively). The results indicate that the difference between the compressibility of the original and remolded samples decreases with repeated loading. It is also observed that the smaller the P min value, the smaller the corresponding difference. Compared with the remolded sample, the original sample has a higher maximum rebound rate ( δ max ) and lower recompression rate ( λ ). When P min is constant, the original and remolded samples show that δ max increases while λ decreases with the increase of P max , eventually becoming the same. Clay is the least sensitive to δ max and the most sensitive to λ . Combined with the analysis of pore distribution characteristics, the results indicate that the medium pores converge to the small pores during compression. The conclusion of this study can provide a theoretical basis and support for the design of underground space in coastal areas as well as for deep and large foundation buildings according to deformation control design.