The Stability Mechanism Research Composite Soil Nailing Structure In Deep Foundation

With the rapid development of China's national economy and the cities, there are more and more deep foundations, which scales and the difficulty of technical requirements are also increasing. So the traditional soil nailing technology can not meet the current needs because of its inherent limitations. As a new type of the supporting structure, composite soil nailing technology is the development of the aditional soil nailing technology, so it has broad prospects for development. However, the research of the stability analysis and the mechanism at home and abroad is still not enough.This paper has applied the methods of theoretical analysis and numerical simulation according to one project. Through the simulation of the excavation and protection, there has a preliminary research about the working mechanism of the common soil nailing and the composite soil nailing technology, the law of the slope displacement and the variation of stress distribution.Based on the existing research results, this paper has described the generation and research of the composite soil nailing technology, and has pointed out some questions which the composite soil nailing technology has, then has discussed the mechanism and unstable mode of the pre-stressed composite soil nailing anchor. It has applied the FLAC3D numerical simulation to make a research about the engineering which use the composite soil nailing by using the Mohr-Coulomb yield criterion. There is a system analysis about the pre-stressed anchor and composite nailing protecting structure. It also discussed the mechanism of composite soil nailing, and the law of the pit deformation and stress vary.The numerical simulation has indicated that the maximum horizontal displacement occurs at the top of the slope, and the pre-stressed anchor can control the displacement effectively. The horizontal displacement and the deformation velocity can increase with the increase of the depth of excavation. The excavation of the soil below has a greater impact on the supporting of the upper free surface. Composite soil nailing structure is mainly affected by tension, and the force is asymmetry. The nails and pre-stressed anchor has undertaken a greater load, so the soil which stay in the support area has undertake a smaller load, that will make the soil play its role of stress transfer and diffusion, so it improves the soil stress concentration. There is a serious stress concentration at the toe of side slope. So at the process of design and construction, there is a need to monitor the toe of the slope. And it prohibits over-excavation and need support timely.