Study On Mechanical Response Law And Umbrella Steel Support Technology Of Shallow Tunnel Construction

In the process of excavation of shallow tunnel,the method of temporary support is often used.The excavation and settlement control of the shallow buried section of the tunnel are the key and difficult problems of the whole tunnel engineering.There are often engineering diseases such as the uneven settlement of the ground surface and the collapse of the side and front slopes.When encountering the settlement problem of shallow buried section,the temporary reinforcement method of vertical steel support is often used for subsequent excavation.However,in the process of tunnel design,the tunnel contour is often set by reasonable arch axis.In this case,there is only axial force and no bending moment in the initial support of the tunnel.When the vertical steel support is added,the stress system of the initial support is changed.Under the action of the surrounding rock earth pressure,the initial support will produce stress concentration and bending moment,which may lead to the local damage of the initial support.Aiming at this kind of engineering problem,combined with the example of SangZhouLing tunnel shallow buried section of Tongzhou ma’aoling section diversion project of yonglincha Road,the monitoring and measurement data of relevant engineering are collected,the cause of the disease is analyzed and investigated,and the shallow buried section of the tunnel is analyzed by finite element method.Finally,combined with the field monitoring data,the stress-strain and settlement displacement of the surrounding rock and initial support in the shallow buried section of SangZhouLing tunnel are compared and analyzed.In view of the shortcomings of the traditional method of vertical support excavation,the improved scheme of umbrella temporary reinforcement excavation of the next step is proposed.The main research work and conclusions are as follows:1)The survey,design,construction and monitoring data of SangZhouLing tunnel are collected.Based on the study of the relevant data of SangZhouLing tunnel,it is found that the reason for the settlement of the tunnel is that under the continuous rainstorm,the rainwater penetrates into the soil mass of the shallow buried section of the tunnel,reduces the cohesion and internal friction angle of the soil mass,increases the self weight of the soil mass,increases the load on the initial support,and causes the settlement of the shallow buried section of the tunnel.2)In this paper,the finite element calculation of the upper bench excavation of SangZhouLing tunnel is studied.Based on the comparison between the deformation data of monitoring and measurement in the upper bench excavation site and the deformation data calculated by the finite element method,the conclusion is drawn that the soil parameters of the investigation data are not consistent with the rainstorm conditions.On the basis of relevant scholars’ research,the soil parameters under rainstorm condition are determined by reducing the soil parameters and trial calculation.3)In this paper,the finite element calculation of the lower step of the original design excavation of SangZhouLing tunnel is carried out.Through the finite element analysis of the original design of the lower bench excavation.It is concluded that the shallow buried section of the tunnel may collapse under this method.4)The finite element analysis of the lower step of the vertical support excavation of SangZhouLing tunnel is carried out.Through the finite element analysis of the excavation of the lower bench with vertical support.It is concluded that local cracking may occur in the initial support of the tunnel under this method.However,this method is feasible in controlling the deformation of surrounding rock.5)In view of the shortcomings of the vertical support,the paper puts forward the method of improving the temporary reinforcement of umbrella support.In this paper,the finite element analysis of the excavation of the lower step with umbrella support is carried out.Through the finite element analysis of the step opening of umbrella support.It is concluded that this method can control the deformation of initial support and prevent its cracking.In controlling the deformation of surrounding rock,this method is slightly better than the vertical support.The above research results can provide a method for the control of surface settlement and initial support deformation and the subsequent excavation of inverted arch in the shallow buried section of SangZhouLing tunnel and similar engineering problems.