Stability Analysis And Control Techniques Of Surrounding Rock Of A Carbonaceous Slate Tunnel With Large Cross-section

ABSTRACT:Xiuning tunnel of the Guangtong-Kunming railway line crossing the slate strata nearly4km, accounting for about30%of the whole tunnel。The construction of the carbonaceous slate tunnel is prone to slump, over excavation and large deformation with its thin layers and low intensity. It is hard to keep the surround rock stability and control the deformation. A study is carried out on engineering properties for carbonaceous slate by a series of in-situ and laboratory tests. Meanwhile, research the control technology of the carbonaceous slate stability and the failure regular pattern surround the tunnel in use of the Site monitoring and Numerical Simulation. The main contents and conclusions of this thesis are as follows:1. Through searching a large number of the related papers, summary and analysis the failure regular pattern of the slate and instability mechanism of the broken rock.2. To take the carbonaceous slate samples from the Xiuning tunnel carbonaceous slate segment. And the water content w, density p, modulus of elasticity E, tensile strength Rm are obtained by in-situ and laboratory tests.3. To obtain the progressive failure of the carbonaceous slate from continuum to discontinuum by using the GDEM software to simulate the tunnel construction in the different dip of carbonaceous slate. Then summary and analysis the deformation and failure law of the carbonaceous slate.4. In construction of the Xiuning tunnel carbonaceous slate segment, the crown settlement and convergence of the tunnel are monitored. Meanwhile, sensors are placed in the representative cross-section of the tunnel to monitor the internal force of steel arch, shotcrete stress, rock pressure, the contact pressure between the initial support and the second lining, etc.Field monitoring results show that, reinforce the surrounding rock ahead and excavate tunnel in seven-step three-stage excavation method can make the deformations of tunnel face and surrounding rocks within the allowable range and the forced state of support structure in good condition by control the excavation length strictly.5. The construction process of the tunnel is simulated in using finite element software MIDAS/GTS, which considers the two kinds of excavation length. By comparing the numerical results it can be found that the crown settlement and convergence of the tunnel, the plastic zone around the tunnel significantly increased with the increase of the excavation length. The forced state of support structure is changing too6. Comparing the field monitoring results with the numerical results, it is found the good agreement between them. Comprehensive analysis shows that reinforce the surrounding rock ahead and short excavation length of seven-step three-stage excavation method can improve the engineering properties of the carbonaceous slate effectively, enhance the stability of the surrounding rock and reduce the deformations of the surrounding rock and the support structure. Meanwhile improve the force state of the support structure to make sure the tunnel excavation safety and efficiency.