| Underground diaphragm wall is a kind of foundation pit enclosure structure,which has the advantages of large wall rigidity,good integrity,fast construction speed,and can be constructed in crowded urban areas or complex geological conditions,etc.,and has good functions of waterproof,water cut-off,seepage prevention,load bearing,etc.,which is usually the first choice for the foundation pit enclosure of subway station.However,due to the over-excavation of foundation pit,the weak support system,the failure of support caused by the construction error and other engineering accidents,the ground and even the wall will be deformed,cracked,or even collapsed,and the serious situation will lead to casualties and direct economic losses.Most of the existing studies focus on the deformation law of soil and the derivation of soil-wall interaction,but the research on the deformation and failure law of reinforced concrete underground continuous wall is insufficient.Therefore,the analysis of the correlation between the damage or failure factors of the underground diaphragm wall plays a guiding role in ensuring the safety of the underground diaphragm wall and the foundation pit itself during the excavation of the foundation pit,so as to guide the actual project.Therefore,based on the monitoring data of subway station foundation pit of Zhejiang university international college station,this paper analyzes the deformation and lateral displacement of the enclosure structure,the axial force of the support,the settlement of the surface outside the pit and other change laws to judge the influence of these factors on the engineering construction.In addition,in actual engineering,the underground continuous wall is a reinforced concrete structure.According to the constitutive model of plastic damage of concrete,the damage evolution law of underground continuous wall in the process of deformation can be given,the crack location of wall concrete can be predicted,and the width of wall crack can be quantified,which plays a guiding role in actual engineering safety.The main research and achievements of this thesis are as follows:(1)According to design data and monitoring report of foundation pit engineering,statistical analysis was made on the monitoring data of wall deformation,support axial force and surface settlement of underground diaphragm wall.The results showed that the wall displacement increases with the increase of the excavation depth of the foundation pit,and the wall presents a parabolic deformation form.The maximum horizontal displacement of the wall is 0.09%-0.14%of the excavation depth.The support axial force increases with the increase of excavation depth,and the support axial force of concrete is larger than that of steel.The surface settlement is between 6.5 and 11mm and shows depression deformation.The surface settlement is 0.01%to 0.015%of the excavation depth.(2)Combined with engineering data,ABAQUS finite element software was used to establish a three-dimensional finite element model of foundation pit,the simulation results were in line with the actual engineering monitoring results,and the correctness and feasibility of the numerical model were verified,providing a basis for further analysis of support position change,foundation pit over excavation and support failure on underground diaphragm wall.Combined with the model,the influence of three factors,the change of the second support,the over excavation of the foundation pit and the soil parameters,on the lateral displacement of the wall and the ground settlement was analyzed.The results show that the maximum horizontal displacement of the wall decreases first and then increases with the decrease of the second support position.The maximum horizontal displacement of the wall increases with the increase in the depth of the foundation pit.the axial force of the first support and the ground settlement increase with the increase of the excavation depth.Among the influencing factors of soil parameters,the decrease of elastic modulus of soil will significantly increase wall deformation and surface settlement,increasing poisson's ratio will increase wall deformation and surface settlement,the increase of cohesion will significantly reduce wall deformation and surface settlement,the internal friction Angle of soil is less sensitive to wall deformation and surface settlement.Deformation and surface settlement decrease with the increase of internal friction angle.(3)Since the failure of the support of the underground diaphragm wall,the foundation pit is severely damaged or even collapsed.Therefore,there are few actual measured data available at present,and most of them are simplified scale experiments.The advantages of numerical analysis can be used to focus on the failure of the continuous diaphragm wall support.The results show that the first failed support wall exhibits cantilever deformation and the wall overturns into the pit as a whole.The horizontal displacement of the wall exceeds the normal value by 781%.Moreover,based on the failure condition of the underground diaphragm wall,the damage of the underground diaphragm wall is analyzed and the crack width is quantified.The results show that when the first support fails,the damage location by the third support location The wall damage value is 0.7 and the equivalent crack width of the wall is 0.71mm,the damage location by the second support location and the wall damage value is 0.76,the equivalent crack width is 6.80mm,and it is a through crack.When the third and fourth support fails,the wall damage location by the first support location.The supporting positions of the roads coincide,and the damage value of the wall is 0.29,and the equivalent crack width of the wall is 0.14mm and 0.15mm.To sum up,the failure of the first or second support is greater than the damage value of the wall when the third or fourth support fails,and the quantified equivalent crack width exceeds the normal use range of structural members. |
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