Optimization Design And Application Research On Deep Foundation Pit Support System

The main idea of this paper include: The choice of retaining method of foundation pit. By considering common retaining structures, the paper discusses the structural features, application fields, functions and mechanisms of pre-stressed anchor and soil-nailing wall and pile-anchor retaining structure. The paper comes up with designing scheme of retaining structures under different conditions and comparison of the schemes from the perspective of cost by taking into consideration the geological conditions illustrated and the actual engineering situation. The paper focuses on two remarkably different retaining structures, with the upper part adopting the pre-stressed anchor and soil-nailing wall and the lower part adopting the retaining pile with multiple anchors. The design adopts deformation control theory, and the paper conducts a safety analysis of the general layout of the design, with a focus on impact factors of the pile anchor retaining structures. The paper also conducts an analysis on the design height, value variation (uniform load or strip load )of upper soil layer, factors of different excavation situations influencing the design of the pile anchor retaining structure, influences of the height variation of upper and lower combination on retaining optimization, and comes up with a safe, reliable and economical design of retaining structure. The paper gives the construction and control points of combined retaining structure, conducts surveying and measuring of excavation of foundation pit with advanced technologies, analyzes data obtained and gives timely feedback to ensure that the retaining structure of the foundation pit is safe, reliable and economical. The conclusion of the paper is as the following:(1) In the soil nail and anchor pile combination support system, the interaction between the force deformation of the two upper and lower support structures is not remarkable, and there will not be an obvious error by means of independent calculation of the two structures in their respective system. That is to say, it is feasible to calculate and analyze separately the upper soil nail support, and then conduct a separate calculation in the lower anchor pile support by means of converting the upper soil nail part to the overburden load.(2) In the design and calculation in accordance with the actual situation, it is economically viable to divide the soil mass load in the upper soil nail support range into uniform load and strip load, and reduce as much as possible the value of the uniform load with the premise to guarantee safety factor.(3) In consideration of the upper bending moment, anchor bolt load, pile top displacement and the slide-proof safety, the vertical height of the upper and lower combination structure has major influence on the safety, stability and cost of the combined support structure, and generally speaking, the height of the upper soil nail wall should not exceed half of the depth of the foundation pit.(4) Designing pile anchor with software guarantees the feasibility of the design length and pull-out strength of the anchor bolt. The stressed situation of the multiple-layer bolts can be adjusted by adjusting the methods of excavation, which effectively balances the pulling forces of different layers and ensures that the soil layer with corresponding bolts provide reliable pulling forces.