Experimental study on compression and rebound deformation characteristics of residual sandy cohesive soil in Xiamen

Through indoor high-pressure consolidation compression and unloading rebound experiments, the deformation characteristics of underlying residual sandy cohesive soil in Xiamen coastal reclamation area under loading and unloading are studied. The test results show that the residual sandy cohesive soil is medium and low compressibility soil. The compression curve of the soil sample gradually slows down and finally stabilizes with the increase of the applied load. In the process of unloading and rebounding, more obvious rebound deformation will occur only when the unloading amount reaches a certain level.The change law of the consolidation coefficient is related to the relative magnitude change between the preconsolidation stress and the current consolidation stress. Generally, it shows a change trend of first decreasing, then increasing, and finally stabilizing. In the unloading rebound stage of the soil sample, there are critical unloading ratio Rcr = 0.25 and limit unloading ratio Ru = 0.75. When 0 < R ≤ 0.25, the soil hardly rebounds. When 0.25 < R < 0.75, the soil has general rebound. When R ≥ 0.75, the soil has strong rebound，and at this stage, the rebound deformation amount accounts for the largest proportion of the total rebound deformation amount. The rebound modulus decreases linearly as the unloading ratio increases. When R exceeds 0.75, the decreasing rate significantly increases. In engineering, R = 0.75 can be regarded as the lower boundary of the strong rebound zone to estimate the depth of the strong rebound zone.