Experimental Study On Underpinning Retaining Method

Support system combined with underpinning pile and soil nailing as a new form of supporting, the working mechanism has a fundamentally difference with other conventional composite soil nailing wall. In order to ensure the safe use of the buildings around the foundation pits, traditional composite soil nail wall is controlled by limiting the horizontal displacement of the foundation pit, and the underpinning pile-soil nailing wall structure is formed by connecting the underpinning pile with foundation of the upper building, taking the initiative to undertake a part of the building load, thereby reducing lateral earth pressure caused by existing buildings. Also underpinning pile and soil nailing wall share the responsibility of lateral earth pressure, limiting the deformation of the buildings and the excavation, it constitutes the underpinning pile-soil nail wall-the upper part of the building structure interaction system, so as to guarantee the safety of buildings and excavation. In this paper, the underpinning pile-soil nail wall supporting system are studied mainly from the indoor model test and the finite element numerical simulation, through the comparative analysis of the experimental data obtained underpinning pile-soil nailing support system in loading and excavation process deformation and bearing mechanism. Mainly have:(1) Under the step loading test, with the increase of the load, the horizontal and vertical displacement of foundation pit is gradually increased, the maximum horizontal displacement of foundation pit occurred in the range of 1.5m in the slope top, middle and upper displacement is relatively large. The internal force of underpinning pile,also increases with the increase of load;(2) In underpinning pile-soil nail wall supporting test, with the increase of the depth of excavation, foundation pit horizontal displacement also increases gradually, the horizontal displacement of foundation pit is large in the middle and small in both ends, At the same time, the ground surface settlement gradually decreases with the distance from the foundation pit; Through three groups of experiments that, in a certain extent, the longer the length of soil nailing, the more obvious the effect of deformation of foundation pit is.(3) Compared with the micro pile composite soil nailing wall, it is concluded that the limiting effect of underpinning pile soil nailing wall support system on the deformation of foundation pit is obvious, the horizontal displacement of foundation pit is obviously smaller than micro pile composite soil nailing wall. In the excavation of foundation pit, underpinning pile-soil nailing wall in supporting pile bending moment and lateral earth pressure were less than the micro pile composite soil nailing wall. It shows that the underpinning pile has a good effect on reducing the lateral earth pressure of foundation pit and the horizontal displacement of foundation pit.(4) In the numerical simulation of underpinning pile-soil nailing wall and micro pile composite soil nailing wall, underpinning pile limit effect of soil nailing wall on foundation pit horizontal displacement and the surface subsidence to significantly larger than the micro pile composite soil nailing wall.