Study On Stability Of Interaction Between Soil And Support Structure During Enclosed Excavation In Deep Foundation Pit

This paper combines specific practice of pipe jacking work well deep foundation pit during enclosed excavation in Chongqing city project of confluence sewage. It mostly studies on the content of the stability of interaction between soil and support structure by means of utilizing theory analysis, numerical simulation, on-the-spot monitor in real time etc. It researches the relevant contents about the soil layer displacement, the earth's surface subsidence, the earth pressure distribution and support structure displacement, support structure stress change etc. that caused in the course to enclosed excavation of deep foundation pit, and has obtained some original achievements. This paper analyzes interaction mechanism between soil and support structure during enclosed excavation in deep foundation by using theory. It has demonstrated, under the ratio of breadth and height is B H<5, that the soil behind support structure exists the soil arching effect, and the stress happens to transform, and the earth pressure state is changed. It also analyzes the reason why the earth pressure state changed, and puts forward the concept that "main stress arching circle". According to the interaction mechanism between soil and support structure, has set up the mechanics models and mechanics expression formulae of the space state. It has also derived out the expression formula of the active earth pressure and passive earth pressure under this situation. In order to describe the interaction mechanism between soil and support structure better, using FLAC3D program to carry on the numerical simulation. The model of numerical simulation is set up by based on test in the on-the-spot room, construction craft, construction procedure etc. It is fully considered the effect of strata during the enclosed excavation. It analyses the peculiar change and development rule of displacement field and force field under space state. It also proves that the soil arching effect existed, which analyses the existence form of "main stress arching circle" and the change law in course of excavation. Through the monitor on-the-spot in real time of deep foundation pit work well in Chongqing city pipeline engineering of confluence dirty water. Summarize the law of the earth pressure distribution , and the law of the earth's surface subsidence, and the law of horizontal displacement of support structure, and the law of the stress changed of supporting structure in little section deep foundation pit excavating. It proves that the soil behind the support structure there are space effects obviously. Using the method of back analysis, comparing through the analysis that the results of numerical simulation with the achievements of monitors on-the-spot in real time, which has demonstrated that the mechanics parameter of the soil body is reasonable, and which has offered reliable scientific basis for optimizing design of support structure.