Abstract
By using the samples of fine sand in Shanghai’s seventh layer, creep tests were performed to investigate the deformation characteristics of fine sand under different groundwater table change. It was revealed that the creep of fine sand is closely related to groundwater table change: when the effective force caused by groundwater table change is smaller than pre-consolidation force, the deformation is mainly elastic. When effective force caused by groundwater table change is bigger than pre-consolidation force, the compression deformation is large and the rebound is small; and the deformation is mainly viscoelastic plastic when equal to pre-consolidation stress. Through the scanning electron microscope (SEM) analysis it was found that creep of fine sand is dominated by the slip of particles, not by the breaking of particles. And the fine sand particles are squeezed under the load induced by the groundwater table change, and the particles slide along the indirect contact surface of the particles, resulting in the continuous adjustment of position and relative displacement. Mercury injection test shows that the pore size distribution of fine sand has little change before and after the test.
Highlights
During construction of deep foundation pit, dewatering needs to be implemented to ensure the safety excavation
For the pore size distribution curves, it can be seen that the four curves of samples are basically overlapped together, which indicates that the particle size distribution of the fine sand is mainly unchanged after creep test, and the percentage of macrospores remained at about 95%
When the load induced by groundwater table change is greater than previous consolidation stress, the compression deformation is large and the rebound is small; and when is equal to the previous consolidation stress, it is mainly viscoelastic plastic deformation
Summary
During construction of deep foundation pit, dewatering needs to be implemented to ensure the safety excavation. The land subsidence induced by dewatering in deep foundation pit involves the creep of soil. Previous studies focused more on the relationship between the material composition and deformation of soil, and rarely combined with the groundwater change mode to explore creep characteristics of soil [6]. The effective stress induced by dewatering is different due to different groundwater table change, and the creep characteristics of soil are often different. The land subsidence induced by dewatering related to the properties of soil itself, and closely related to the changes of groundwater table experienced by soil layers [7]. Taking the typical soil of fine sand in Shanghai’s seventh layer as example, tests were conducted to investigate the creep deformation characteristics under different groundwater table changes. It is of great importance to reveal the mechanism of land subsidence induced by dewatering, and it is beneficial to strengthen the control of land subsidence
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