Study On Large Deformation Mechanism And Construction Control Technology Of Red-bed Soft Rock Tunnel With High Ground Stress

Large deformation disasters are prone to occur during the construction of soft rock tunnels in red beds with high ground stress,which seriously affect the construction safety and engineering progress of tunnels.A large number of studies have been carried out on the large deformation problem of soft rock tunnel with high geostress,but the large deformation problem of tunnel has not been effectively solved.Based on the key project of science and technology research and development plan of China Railway Co.,Ltd.(2021-key-09),combined with the actual project,using the field test,theoretical analysis and numerical simulation method,this thesis deeply studies the catastrophic mechanism of large deformation,the calculation method of surrounding rock pressure and the construction control technology of tunnel crossing high stress red layer soft rock stratum.The main work and achievements are as follows :(1)Based on the field deformation monitoring and in-situ stress test data,combined with the existing research results on the mechanical properties of red-bed soft rock,the catastrophic mechanism of large deformation of red-bed soft rock tunnel with high in-situ stress is analyzed.The red-bed soft rock exceeds its yield strength under the action of high insitu stress,and then large deformation occurs.The softening and expansion of rock mass aggravates the deformation development.The high temperature environment of tunnel leads to the delay of the construction of primary support and secondary lining,which makes the deformation grow rapidly.The rheological effect of rock mass and groundwater promotes the occurrence of large deformation.(2)Based on the nonlinear Hoek-Brown strength criterion,considering the softening and dilatancy characteristics of surrounding rock under high geostress,the theoretical calculation method of surrounding rock pressure of red-bed soft rock tunnel with high geostress is established,and the characteristic curve equation of surrounding rock pressure of redbed soft rock tunnel with high geostress is further obtained.(3)According to the established surrounding rock characteristic curve of red-bed soft rock tunnel with high geostress,based on the basic principle of convergence constraint method,the stability of support structure in redbed soft rock section of Xinhua tunnel with high geostress is analyzed.The analysis results show that the original design scheme cannot meet the deformation control requirements of red-bed soft rock tunnel with high geostress,and the influence of surrounding rock softening and expansion effect cannot be ignored in the design and stability analysis of tunnel support structure.(4)Taking the strength-stress ratio of surrounding rock as the standard,the large deformation level of Xinhua tunnel is divided into three levels :slight,medium and severe.By using numerical simulation method,considering the softening and expansion effect of surrounding rock,the construction control schemes under different large deformation levels are determined,and the construction disposal process of large deformation section of tunnel is proposed.