| According to the Mid-term and Long-term Railway Programming established in2008, there will be more than5thousand tunnels in next ten years. The length, which will be9000km, will surpass that of sum of the existing railway tunnels. There are many tunnels in our country, but it is not expert in design tunnels, because the design technique is at a semi-empirical and semi-theoretical stage. It is a new challenge to the present design theory, when tunnels are under geotechnical conditions of big depth, large section and fragile surrounding rock. The methods of experiment, simulation and analytical analysis are used to study determination method of supporting load and structural form of composite surrounding rock, which is the key problem of Control Theory about Tunnel Structure and Stability, when tunnels are under above condition. Some conclusions are achieved as following.(1) Deformation and failure mechanism of surrounding rock is researched by experimental method. Artificial speckle field is developed, which is applied to simulation experiment with analogy material. The evolution rule of surrounding rock deformation field is observed by DSCM in progressive failure experiment. Observation results indicate that a shear fracture zone of "V" form first appeared in arch waist during loading process, and as the load increasing, the shear failure in arch waist formed an arch or half arch cracks expanding to the scope of above vault.(2)A secondary and verification of strain softening constitutive model is also realized. According to the plastic potential theory, incremental iterative format of damage constitutive model in FLAC3D is deduced, and interface procedures of secondary developed FLAC3D are compiled. The secondary developed procedures are used for the engineering and the analytical results validated the correctness of the program. Analysis indicate that degradation of deformation modulus has great affect to the deformation of surrounding rock, and when comparing to Mohr-Colomb model calculation results, damage constitutive model can better reflect the damage characteristics and deformation and failure mechanism of surrounding rock in the self weight stress field when the tunnel is deep buried.(3) Structure layer surrounding rock was analyzed by using experimental method. Pressure boxes are used to monitor the change regulation of surrounding rock during the loading process in the progressive failure experiment. The monitoring results of Pressure box show that structure layer state of surrounding rock in deep buried tunnel is from loosened zone to arch of pressure arch to original stress zone.(4) By using degradation damage constitutive model of FLAC3D, structure layer state of surrounding rock in deep buried tunnel are studied by numerical simulation. And the influences of lateral pressure coefficient, buried depth, rock level to structure layer states are studied through numerical simulation. Analysis shows that structure layer state of surrounding rock in deep buried tunnel is as following three states, deterioration serious damage zone (loosened zone) where tangential stress is lower than the original rock stress region, pressure zone where tangential stress is higher than the original stress zone, the original stress zone which is at the outside of pressure arch. Coefficient of lateral pressure has a great influence on the shape of structure layer in surrounding rock. When the lateral pressure coefficient under certain conditions, buried depth and grade of surrounding rock have a great influence on structure layer range, and also determine the forming arch conditions of pressure arch.(5) By using three linear stress strain softening model which is from elasticity to plastic softness to plastic residue, also considering the dilatancy effect, the stress and displacement analytical solution at any point in the surrounding rock is deduced. The physical concept deep or shallow rock is put forward based on the analytical solution of the displacement and stress distribution characteristics. The Shallow rocks are at plastic residual state, reaching the residual strength and a larger displacement, needing to have reinforcement and treatment. Deep surrounding rocks are in the plastic softening and elastic stress rising zone, having relatively small displacement, bearing itself loads and most rocket loads. Surrounding rock mechanical properties have a significant impact on the range of deep or shallow rock. Finally, rock pressure of deep or shallow surrounding rock to supporting structure is analyzed, the calculation method of strain softening model and surrounding rock characteristic curve, when considering dilatancy property, is proposed.(6) Determination methods of supporting load is obtained with tunnel supporting structure at the certain deformation. First, deep rock, shallow rock and the supporting structure are as support systems of Winkle model with different stiffness, and the mechanical model of support system is also established. Supporting load includes two part, one is because of deformation in deep rock, the other is because of loose in shallow rock. If the lateral pressure coefficient is1and the tunnel section is circular, supporting load can be obtained by using analytic method. If the lateral pressure coefficient is not1 or the tunnel section is not circular, supporting load can be obtained by using numerical method.(7) The layer situation curve describes changing rules of supporting load with different support, when there are displacements in the walls. Method to determine layer situation curve is given by analytical methods. The analysis shows that layer situation curve reflects the actual working conditions of supporting structure and the dynamic relationship between supporting structure and rock; it also indicates the best supporting opportunity and the most reasonable allowed displacement.
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