Numerical Simulation Study On Construction Mechanical Behavior Of Deep And Large Shaft In Permeable Strata

With the development of urban construction in our country, major cities are building a large number of subways. There always is a vertical shaft among running tunnel between subway stations. The safety of the shaft directly affects the subway and the surrounding environment. The mechanical behaviors of the shaft structure in construction process are more complex in strong permeable and water-rich formation. How to ensure the safety of the shaft in construction process is a problem that needs to be urgently solved.This thesis is based on the airshaft between the Olympic Sports Center and Century Avenue of No.1 rapid rail transit engineering in Lanzhou city. To study on the mechanical behavior of supporting structure of foundation pit, a fluid-solid coupling method is adopted. And four cases in different ways of water plugging were calculated with FLAC3D software. Therefore, the mechanical behavior of structures is studied, and the main achievements and conclusions are as follows:1. The variation of precipitation depth changes the existing distribution of pore pressure. A large value of hydraulic gradient is formed within the specific scope of the outside of diaphragm wall. Water in the bottom of pit has a tendency to upwell. Equipotential lines of pore pressure are concave in the bottom of diaphragm wall.2. With the soil excavation in shaft, the displacement and internal force become more and more large. The maximum horizontal displacement of retaining structures tends to occur near the excavation face. The increment of precipitation depth and grouting technique change the distribution of soil pressure and improve the stress states of the retaining structure and the main structure. At the same time, these strategies effectively suppress the bottom heave and make the shaft more secure. However, the increment of precipitation depth exacerbated the ground surface settlement, and particular attention should be paid on.3. Openings in shaft during shield driving may affect the overall stability of the shaft. Through study, we find that the stability of shaft is affected slightly by openings the holes in the shaft wall during shield driving.