Application And Numerical Simulation Of Sparse Pile-Soil Nail Wall Retaining Structure

With the rapid development of economic, urban construction is progressing with each passing day. In the process of building sustainable cities, Development and Utilization of Underground Space play a very important role, witch is not only an important means of regulating the land use structure of urban and expanding space of the city, but also an important way of establishing an integrated modern city transport system, an integrated space systems for disaster prevention and relief, meanwhile, it has been the primary method to establish modern urban infrastructure. Therefore, in order to make full and rational use of urban underground space, a large-scale excavation and support of foundation excavation engineering is becoming necessary. As a result of meeting requirements of building structure and application, area of excavation is growing; foundation has developed from original depth of about 5m to the current depth of nearly 40m.Deep foundation excavation engineering is usually intensive in the urban buildings, with narrow space, complex geological conditions and surrounding environmental conditions, and major technical difficulty of construction, which is unprecedented. In addition to ensuring the stability of its foundation, digging deep foundation excavation engineering must also ensure the safety of the nearby building facilities, so digging deep foundation excavation in the narrow space will not only bring great difficulties to support design, but also bring great threat to the safety of the approach building.Composite soil nailing walls supporting structure is a new technology, which is developed from the basis of soil nailing, and for pitting foundation or increase stability of the slope. A large number of engineering has practice in China urban construction. But inferior theory of composite soil nailing walls supporting structure is behind the practice, imperfection of design and analysis methods, limited pilot studies, also limited the development of this technology. Sparse pile - soil nail retaining wall structure is a new type support of composite soil nailing walls, witch is formed on the basis of summarizing limitations of pre-stressed cable composite soil nailing walls and micro-pile composite soil nailing walls the .This article pointed out that the main limitation of composite soil nailing walls is the limited depth of excavation and difficulty to forecast and effective control. According to stability analysis mixing piles, root bored piles cable composite soil nail wall, a conclusion is reached that insufficient bending and shearing capability of mixing piles (root bored piles) are main restraining factors to depth the of composite soil nailing walls Supporting Foundation in the soft soil layer. Sparse pile-soil nail retaining wall type have advantages of strong sparse pile bending ability, and soil resistance ability supplied by soil arching witch is supported by composite soil nailing walls. With the condition of limited increase or even decrease in the cost, the stability of support was greatly enhanced.Sparse pile - soil nail retaining wall system as a relatively new form of support, this article analyzes the mechanism of support structure, sparse pile - soil nail retaining wall system is effective integration use of initiative support with the passive support. We control soil deformation of the excavation process and improve the stability of foundation in the early time through advanced supporting of piles, Because the soil nail wall displacement occurs mainly in the time after lower earth excavation, and before completing lower soil nailing construction, advanced pile support can greatly reduce this part of displacement. At this point piles have insertion depth and higher stiffness and strength, so border restrictions is been strengthening, plastic deformation within the soil is undermined. Position of bolt strength the set of such constraints, limits the development of soil displacement. With the increased depth of excavation, interaction of soil nails and reinforced soil resistance the stress and strain from the damage trend of the foundation. Sliding body slid down at the condition that advantage control surfaces form finally. At the beginning of formation of advantage sliding control surfaces, slipping cracks happen on the ground appears as a guide, and changes in the development rate. We use sufficient "suture strength" soil nail "suture" advantage slipping control surfaces, and than, this surface will not slip initiation, or not develop. If the excavation depth is too large, when part of the slip surface excels the width scope of soil nailing wall, the stabilizing effect of soil nail on the overall become relatively small, bolt will play its greater role, and constitute a pile anchor block soil system with the piles.This article use equivalent beam method to design pile-anchor, and check its stability; soil nailing design use limit equilibrium method, and correct it is reasonable through checking its stability, in checking the stability, LIZHENG software is used to the Compare and check.Finally, I do three-dimensional structure FLAC-3D simulation to sparse pile - soil nail combination retaining wall, through the analyzing and fitting with the measured data I find: the law of horizontal displacement and settlement in the excavation process reveals that sparse row piles, pre-stressed anchor and soil nail retaining wall system play an active role in controlling the horizontal displacement and the settlement; Foundation soil at Lateral of great stress arch is reliability supported, the critical damage body is related to extend to the surface at 35°with horizontal level; plastic zone of sparse pile - soil nail wall supporting structure foundation soil gradually broaden and develop with the progressive of excavation, and expand gradually from the top to the foot, than, occur strain concentration area; With further foundation excavation, plastic zone will be near the foot of the slope, and it gradually develop at two directions of approaching and getting away from excavation wall in the horizontal level, and ultimately cross the plastic zone .In this paper, a project is selected focusing on a Shenzhen city deep foundation excavation engineering, with calculation, analysis, stability check, the use of numerical simulation analysis, the calculation results, monitoring data and numerical simulation results of the analysis, which turns out to be in a very good consistency. It indicates that the project design is reasonable and effective, which provides the practical value and theoretical significance for future design and construction of sparse pile - soil nail combination retaining wall.