Study On Stress And Deformation Characteristics Of Semi-rigid And Semi-cover Excavation System

Based on the Lv Cuo Station Project of Xiamen Rail Transit Line 2,this paper takes the semi-rigid and semi-cover excavation structure system as the research object,and uses the means of theoretical analysis,numerical simulation and field test to combine the method of theoretical analysis,numerical simulation and field test.The deformation and mechanical properties of semi-rigid and semi-cover excavation system are studied in this paper.The following preliminary conclusions have been reached:(1)The internal force analysis of semi-rigid and semi-cover excavation system is carried out by using the improved increment method.The results show that the bearing capacity of the structure meets the requirements.The cover plate is the weakest part in the whole structure system,which is the control factor of the safety of the structure system.(2)By comparing the numerical analysis results with the field test results,it is concluded that the deformation of the semi-rigid and semi-cover excavation foundation pit ground continuous wall is "big belly",and the corner and the edge corner of the ground continuous wall have the restraint effect on the deformation of the ground connecting wall.On the side of vehicle load,the closer to the ground wall,the larger the ground settlement value is,the smaller the ground settlement value is,and the smaller the surface settlement value is,on the side of no vehicle load,the curve of surface settlement is a "groove" type.Under the condition of self-weight of cover plate under construction load,the settlement of column shows the trend of continuous subsidence,which leads to the settlement of column at the end of the foundation pit is smaller than that of the column in the middle part of the foundation pit.Concrete The trend of the axial force of the brace decreases first and then increases,and the axial force of the steel bracing increases with the excavation.(3)Through the comprehensive analysis of the theoretical calculation results,numerical analysis results and field test results,it is concluded that the internal force of the structure does not exceed its bearing capacity and the surface settlement in the whole excavation process of the half-cover excavation and semi-rigid foundation pit.The horizontal displacement of the wall,the axial force of the concrete support,the axial force of the steel support and the settlement of the column do not exceed the control value,which indicates that the semi-rigid and semi-cover excavation system of the project has a large safety reserve.It is safe and feasible under the combined load of slag-soil vehicle load and urban traffic load.(4)Through the comprehensive analysis of the stiffness of the cover plate,the bearing capacity of the column,the stability in the plane under the action of the moment of the column,the axial force of the support and the horizontal displacement of the wall on theground,it is concluded that the limit value of the load on the one side of the column is 45 t.And when the cover plate takes 45 t slag-soil vehicle,the maximum deflection value of the cover plate reaches its allowable value,while the calculation of the column cross-section strength and the overall stability in the plane under the action of the bending moment,the horizontal displacement of the wall on the ground,The axial force of concrete brace and steel brace exceeds the corresponding allowable value and control value.It is concluded that the critical load control factor of semi-rigid and semi-cover excavation system is also the cover plate.