Analysis Of Deep Excavation Considering Changes Of Void Ratio And Permeability Coefficient With Soil Stress

According to engineering actuality that soil void ratio and permeability coefficient change with stress state during deep excavation, a numerical model based on Modified Cam-Clay model and considering the impact of changing soil void ratio and permeability coefficient, is constructed by using the software ABAQUS and its secondary-development platform. Then three simulation tests, one of which considers both the impacts of soil void ratio and permeability coefficient changing, another considers only the impact of soil void ratio changing, another considers neither of them, are carried out for contrastive analysis. The main achievements of the research and conclusions given by the simulation results are summed up as follows.(1) Relations of soil permeability coefficient to its void ratio and void ratio to stress state are described by different reasonable formulas, respectively. Two user subroutines related to the formulas are compiled for numerical modeling. And the model is proved to be practicable in deep excavation analysis after comparing its simulation results with test data and other research results.(2) The contrastive analysis results of the simulation considering only the impact of soil void ratio changing and that considering neither of them, indicates that when considering only the impact of soil void ratio changing, the maximum horizontal displacement of diaphragm wall, the maximum ground settlement are about 28%,110% larger than that considering neither of them, and also the deep soil settlement and horizontal displacement of soil above excavation depth of the former are much larger than that of the latter, while the bottom heave is about 31% smaller.(3) The results of the simulation considering both the impacts of soil void ratio changing and permeability coefficient changing, are compared against that considering only the impact of soil void ratio changing. It is shown that the maximum horizontal displacement of diaphragm wall, the maximum ground settlement, the maximum bottom heave and the maximum bending moment of diaphragm wall considering both the impacts of soil void ratio changing and permeability coefficient changing are about 30%,25%,10%, and 12%smaller than that only considering the impact of soil void ratio changing, respectively. And the deep soil settlement and horizontal displacement of soil above excavation depth of the former are much smaller than that of the latter(4) By comparing the results of the simulation considering both the impacts of soil void ratio changing and permeability coefficient changing and the simulation considering neither of them, it turned out that the maximum horizontal displacement of diaphragm wall, the maximum bottom heave and the maximum bending moment of diaphragm wall considering both the impacts of soil void ratio changing and permeability coefficient changing are about 10%,38%, and 5% smaller than that considering neither of them, respectively. While the soil settlement outside the pit considering both the impacts is much larger than that considering neither of them.(5) The simulation considering both the impacts of soil void ratio changing and permeability coefficient changing can reflect the influence of dewatering much better than the other two. Therefore, it is necessary to consider the changes of void ratio and permeability coefficient with soil stress in the numerical analysis of deep excavation.