Experimental study on influence of foundation pit dewatering on soil permeability

Aiming at layer 3 (mucky silty clay), layer 4 (mucky clay), layer 5-1 (silty clay) and layer 5-2 (clayey silt) involved in the process of excavation dewatering in soft soil stratum of Shanghai, a study was made on the influence of foundation pit dewatering on the soil permeability through the two step consolidation method and variable head permeability test. The test results show that: (1) as the drawdown increases, both the vertical permeability coefficient and the horizontal permeability coefficient of the soil decrease, and finally they tend to be stable. (2) for the vertical permeability coefficient, the K-v value of Layer 5-2, layer 3, layer 4 and layer 5-1 decreases 20%, 10%, 5%, 3% per drawdown respectively, and for the horizontal permeability coefficient, the K-h value of Layer 5-2, layer 3, layer 4 and layer 5-1 decreases 12%, 6%, 5%, 2% per drawdown respectively. (3) the horizontal permeability coefficient for each layer is 1-5 times larger than the vertical permeability coefficient. In the end, the simplified calculation formulas of the soil permeability coefficient are obtained based on the theory of regression analysis, which provides reference for determination on the permeability coefficient of the soil during dewatering of foundation pit.