Research On Pulling Out Profile Steel Of Grout Micro-pile In Foundation Pit Of Loess Area

With the rapid development of urban construction,a large number of municipal projects are put into construction,especially underground pipe corridors and urban subways involve underground space development,but most of the projects are located in busy streets,and the construction is greatly affected by the environment.Generally,micro piles are used to support The technical foundation pit project often faces the problem that its piles and built-in reinforced materials remain in the original soil,which affects the subsequent utilization of underground space.In this paper,the cement-soil grouting micropile is taken as the research object to study the mechanical performance and load transfer mechanism of the section steel during the removal of the section steel,so as to realize the recycling of the section steel built in the micro pile.The main research contents and conclusions are as follows:(1)In this paper,the unconfined compressive strength test and triaxial compression test of cement loess were carried out,and the influence of cement mixing ratio on the strength of cement loess was analyzed.The test results show that with the increase of the cement content,the unconfined compressive strength and elastic modulus of the cement soil gradually increase;the cement loess has the characteristics of brittle materials.As the cement mixing ratio increases,the cement loess’ s The peak strength and residual strength gradually increase,and at the same time the initial tangent modulus is increased;the shear strength index of cement loess can be obtained by drawing the stress Mohr circle.The results show that the increase of cement mixing ratio increases the internal friction angle φ and The cohesion c has improved to varying degrees.(2)In the field test,through the design of different cement incorporation ratio and whether to apply anti-friction agent for the test pile section steel removal,the removal load-displacement curve of the section steel,axial distribution of the section steel axial force and shear stress were analyzed.The results show that the section steel removal can be roughly divided into four stages: slow sliding stage,rapid sliding stage,ring breaking stage and horizontal stage;the ultimate load for removal increases linearly with the cement incorporation ratio,and the residual load of the steel with antifriction agent applied About 59% of its ultimate load,the ratio of uncoated anti-friction steel has increased;at the same cement content,the ultimate load of steel with antifriction agent is about 49% of the steel without anti-friction agent.(3)Use the ABAQUS finite element software to establish a finite element model of the field test pile and compare and analyze the results with the field test.The results show that the finite element simulation results are in good agreement with the field test results,indicating that the finite element model parameters are set reasonably,and the finite element model can more accurately reflect the stress of the steel during the removal process;in addition,the use of finite element software for different sizes The simulation of the removal of the steel section shows that the relationship between the unit shear stress and the contact area is not obvious,and it is related to the surface condition of the bonding interface between the cement soil and the section steel.