Study On The Impact On The Excavation Of Deep Foundation Pit By Groundwater In Tianjin Area

The problems caused by ground water are unavoidable during the excavation of foundation pit engineering in soft fields containing plenty of ground water. The seepage field and the stress field will be changed as the ground water level changes. Therefore, it would be of great theoretical value as well as engineering practice value to study the manual interaction mechanism between ground water and soils and the impact of seepage function on the foundation engineering, and obtain the specific data of the changes of soil structure as the ground water level changes. This thesis studies the impact of ground water on the excavation of foundation pit based on a certain engineering in Tianjin area.Firstly, the hydrogeological conditions of Tianjin area are comprehensively evaluated. Through analyzing the formation of the stratum and the lithology, the formation and status of ground water is studied. The motion characteristic of the ground water is obtained based on the analysis of the hydrodynamic connection between each aquifers and the ground water and the ambient water, which lays the foundation of the afterwards studies.Secondly, different kinds of geologic hazards caused by ground water are synthetically analyzed. This thesis studied the resisting of uplift effect of the pit bottom, and analyzed the mechanism of uplift effect, based on which, the corresponding countermeasures are brought up. Also, the mechanism of piping, surging and soil flowing are studied, and the numerical prediction equations are established, at last, the countermeasures for each geologic hazards are brought up.Based on the synthetic analysis of hydrogeological conditions, this thesis studied the coupling effect mechanism between seepage field and stress field according to Darcy's Law, Dupuit Hypothesis and The Principle of Effective Stress, and established the coupling model of seepage and stress.At last, this thesis took the specific engineering of the second line of Tianjin metro as an example, calculated the interaction connection between the seepage field and the stress field, and achieved the numerical relevance of the void ratio and the settlement as the ground water level descends, furthermore, the specific relevance between the permeability coefficient and the soil structure are obtained.The study based on this thesis provides valuable instructions for the designing, construction of the dewatering excavation.