Research On Large Deformation Control Technique Of Soft Surrounding Rock In Complex Crustal Stress Tunnel

The cause for large-scale deformation in tunnel lies in that:on the one hand, expansion effect of expansive material ingredient leads to large deformation in tunnel; on the other hand, weak soft rock occurs extruded deformation under the effect of complicated stress. Due to complexity of stress and low strength of rock, once the tunnel is excavated, extensive plastic damage area will appear. The shearing and extruding effect occurs on rock in plastic area, and forces the mass to move toward excavation space, thus, large deformation is resulted in.In view of the various reasons, such as uncertainty of geological condition, unreasonable excavation method and supporting measures, collapse is easy to take place during tunnel construction in extruded weak and soft rock area, which affects construction safety, duration and investment. Therefore, selection of reasonable supporting measures and construction plan are critical for control over large deformation of extruded weak rockmass.In this article, combined with construction of Baozhen tunnel in soft, weak and large deformation rock area on Yiwan railway, many measures, such as site measurement, theoretical analysis, numerical simulation, indoor test and artificial intelligence, were integrated to execute the following studies:(1) Study on site measurement method, data analysis and testing content includes rock deformation monitoring and each optional test item.(2) Intelligent forecasting method of large deformation in soft and weak rock area during construction of Baozhen tunnel.(3) Large deformation mechanism and structural parameter optimization for soft and weak rock of Baozhen tunnel.(4) Elasto-plastic back analysis of physical & mechanical parameters and initial crustal stress field for soft and weak rock of Baozhen tunnel in three-dimension.(5) Determination of reserved deformation for soft and weak rock with high crustal stress.(6) Large deformation classification standard of soft and weak rock with high crustal stress and corresponding engineering measure.(7) Displacement control benchmark for large deformation section with high crustal stress in Baozhen tunnel. Through statistics and analysis on site measurement data, and in combination with theoretical analysis and numerical simulation, following results can be obtained:(1) The decimal genetic algorithm was used to search the optimal topological structure parameters of BP network during it's training process and corresponding calculation code was programmed. This algorithm and program were applied in large deformation prediction of Baozhen tunnel by multi-step rolling method. The application result indicates such algorithm has extremely high forecast accuracy, which provide reliable guarantee for predicting final deformation and determining best time of secondary lining.(2) Evolutionary neural algorithm was used to inverse the physical and mechanical parameters of rockmass and initial crustal stress in large deformation area, and the inversion results are used to forecast short-term rock deformation in subsequent excavation. From the applying result, it can be concluded that this method possess high forecasting accuracy.(3) Calculation formula for rock reserved deformation in different stratum structure is proposed to determine reserved deformation control standard for large deformation of rock stratum composition with different rock properties.(4) The factors, such as compressive strength, crustal stress, plastic modulus and side pressure coefficient are considered as a whole to determine the a classification standard of large deformation in Baozhen tunnel. The comprehensive index judgment method for deformation level classification was put forwarded, and the prevention and treatment measures for different-level large deformation were presented clearly.(5) Displacement control benchmark in large deformation area with high crustal stress is determined. The construction condition and engineering measures under different management level and managed displacement are proposed.Above mentioned study results had been applied in construction of Baozhen Tunnel in soft and weak rock area with large deformation, which ensures construction safety and project quality of the tunnel, and provides guidance for similar engineering design and construction effectively.