Research On Technology Of Foundation Pit Supporting Under The Condition Of Discontinuous Foundation With Cap And Multi-pile

Foundation pit excavation engineering closing to the existing buildings are widespread in the urban construction. In order to protect the foundation pit and the existing buildings, We often select the supporting structures which cost is higher. If there exists a building with discontinuous pile foundation with cap and multi-pile beside the foundation pit, this article will consider the pile foundation of the existing buildings as pile bearing horizontal load, then use of the soil arching effect between the discontinuous pile foundation, thus the horizontal load behind the soil arch will transmit to the pile foundation. For the soil between the pile foundations we can adopt soil nailing wall to support. So we will make full use of the pile foundation of the existing buildings and the soil nailing wall, and they will perform together to make up the supporting system.Three-dimensional finite element model is established by ABAQUS. This article respectively simulates the soil arching effect between the discontinuous pile foundation with cap and multi-pile when there is no supporting structures, and the supporting characteristics of the existing buildings and soil nailing wall composite supporting structures. And through the calculation of engineering case, this article analyzes the design method of the composite supporting structure. This article mainly summarizes the formation conditions of the soil arch, analyzes the formation process and appearance of the soil arch between the discontinuous pile foundation with cap and multi-pile. What`s more, the soil arching effect and the load transfer law of pile foundation and soil nailing wall in the composite supporting structures are studied. The main conclusions obtained state as follows:(1)The soil arching effect is forming and changing with the excavation gradually. And it`s formation and destruction process are accompanied with the stress transferring, zone of stress arch forming and damaging. The development of the soil arch can be divided into three stages: initial stage, part of the plastic stage, final stage. In the excavation, only when the slip surface locates behind the arch crown, there will appears complete soil arching effect;(2)In the existing buildings and soil nailing wall composite supporting structure, the soil arching effect has no effect on the vertical bearing capacity of the piles, and mainly pass the horizontal load to the first row of pile. The zone behind the pit can be divided into four parts: the confining region in front of the arch, the confining region behind the arch, the compacting region behind the pile and the stable region. There is a sharp drop period of soil nail axial force after the confining region in front of the arch, but the trend of the steep fall weakens with the increase of depth soil nailing buried;(3)After calculated the engineering example, compared with the results of numerical simulation and the norms, as a economical and reasonable form, the existing buildings and soil nailing wall composite supporting structure can be applied to the foundation pit engineering closing to the buildings.