| With the rapid development of underground space engineering,the form of foundation pit engineering support structure has always been the focus of research.Qingdao Metro Anshan Road Interchange Station is located at the intersection of Anshan Road and Shandong Road in North District of Qingdao,the stratum is a typical "soft upper and hard lower" soil-rock composite stratum in Qingdao area,and the local burial depth of the foundation pit reaches 40 m.The upper layer of the foundation pit is covered with soil and the lower layer is granite with high strength,the micro steel pipe pile anchor support has obvious advantages in this stratum,the micro steel pipe pile construction is convenient and flexible,which effectively solves the problem that the support pile is difficult to construct in the hard rock layer.The support system can effectively control the structure of the This kind of support system can effectively control the deformation of deep and large foundation pits of soil and rock,and its deformation characteristics and support characteristics are worthy of further study.In this paper,by summarizing the previous research results,analyzing the common support methods and the characteristics of micro steel pipe pile and anchor support system,and taking the soil-rock composite deep foundation pit of Qingdao Anshan Road as the engineering background,the study of the force deformation of the enclosure structure during the whole process of foundation excavation is conducted to summarize the deformation law of the enclosure structure during the graded excavation.The numerical model is created and the calculation results are compared and analyzed with the measured data.Finally,the main factors affecting the micro steel pipe pile anchor cable support system are discussed,and the influence of three variables on the deformation of the support structure,namely the number of micro steel pipe pile rows,the value of pre-stressed anchor cable and the depth of pile embedment,is studied as follows.(1)Review the previous literature on the application of micro steel pipe pile anchor cable support structure in foundation pit engineering,summarize the characteristics of foundation pit deformation in different areas and under different support structure conditions,introduce the characteristics of several common support forms,propose the limitations of the current support structure for excavation support of deep and large foundation pits with soil-rock composite in Qingdao area,and analyze the mechanism of action and main damage forms of micro steel pipe pile anchor cable support structure.(2)Three typical support units of Anshan Road Station are monitored during the whole excavation process,and the monitoring objects mainly include the horizontal displacement of pile top,vertical displacement of pile top and internal force of anchor cable,and the innovative Canadian ESG microseismic monitoring system is introduced to monitor the real-time damage status of the lower surrounding rock of the soil-rock composite foundation pit,and explore the correlation between microseismic events,pit displacement and internal force of anchor cable during the excavation process of foundation pit.By analyzing the monitoring data of the whole process of foundation excavation,the deformation characteristics of each stage in the process of graded excavation and the deformation control effect of this support system are studied.(3)Create a three-dimensional numerical model of soil-rock deep foundation pit and analyze the deformation characteristics of the soil-rock combination pit under the conditions of double-row miniature steel pipe pile + prestressed anchor cable in the first stage and single-row pile + anchor rod support in the second and third stages.The numerical calculation results are compared and analyzed with the actual measured data to verify the reliability of the numerical calculation results.Exploring the rationality of micro steel pipe pile anchor cable support structure applied in the excavation process of soil-rock composite foundation pit by analyzing the numerical simulation results.(4)By changing three factors,namely,the number of piles in the first stage of the support structure,the value of anchor cable pre-stress and the depth of pile embedment,the influence of several factors on the support effect of the support system in the soil-rock composite foundation pit is studied.By analyzing three numerical calculation data of pile horizontal displacement,bending moment and shear force,the influence of several factors on the deformation of the support system is summarized,and the value of the design parameters of the support structure of this foundation pit is optimized to provide reference for similar foundation pit projects. |
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