Experimental Investigation Of Working Principle For The Composite Supporting Structure Of Upper Soil Nailing Wall And Lower Anchor Pile (Bracing)

With the rapid development of economy in our country, people also put forward higher requirements for foundation pit supporting structures, the traditional supporting structures cannot meet this requirement very well. The upper soil nailing wall and lower anchor pile (bracing) composite supporting structure takes account of the advantages both of the pile anchor supporting structure and inside supporting structures. Not only can it enhance advantages but also circumvent weaknesses. Yet the related researches on this composite retaining structure obviously lag behind the demand of the engineering.This paper bases on the deep foundation pit engineering of the rand international center in Zhengzhou. The displacement of the surrounding foundation pit and main parts of the supporting structures has been monitored in site during the process of excavation of foundation pit; the monitoring data has been analyzed. The law of displacement of the foundation pit with supporting of the upper soil nailing wall and lower anchor pile (bracing) composite supporting structure has been summarized. ABAQUS has been used to simulate the whole process of excavation, the model and parameters shows rational and applicable according to the comparison between simulation result and monitoring data. The influence from design parameters on displacement of foundation pit and supporting has been summarized by changing design parameters for the virtual design. The paper mainly got the following conclusions:(1) It will be better if the height of the soil nailing wall is between three to six meters when the composite supporting structure is used in this type of soil in Zhengzhou, and it should not more than6meters.(2) Should ensure that the beam elevation is higher than the bottom of the surrounding foundations where the upper buildings need to be protected during the process of choosing supporting structures.(3) The under supporting system of pile anchor (bracing) do little to the stability of the upper soil, and the design of the upper soil nail wall should be done based on its own strength and stability.(4) The deep horizontal displacement curve of piles in the composite supporting structure of upper soil nailing wall and lower anchor pile (bracing) is generally presents the "P" shape, at the same time, the maximal displacement appears near the reinforced concrete brace position.(5) It is necessary to set up interior bracings in the interval of upper one-third of the piles if the restriction of deformation is strict. For the deep excavation, inner bracing should be added where the active earth pressure of the under supporting structure is large.