Study Of Engineering Properties And Grouting Technique For Mylonite Of Xiuning Tunnel Exit Zone

Based on construction project of the Xiuning tunnel exit zone in the Guangtong-Kunming railway line, a study is carried out on engineering properties forⅥgrade mylonite by a series of in-situ and laboratory tests. Meanwhile, grouting technique of the test section in tunnel exit zone is investigated. The main contents and conclusions of this thesis are as follows:1.The mylonite samples are taken from the section which is not grouted in the Xiuning tunnel exit zone. The water content w, densityρ, specific gravity Gs, cohesion c, internal friction angleφand other physical parameters as well as mechanical parameters are obtained by in-situ and laboratory tests. The composition of particles of mylonite sample is analyzed; in addition, the water stability of shear strength is studied. The experimental results show that the cohesion of mylonite increases with the increase of water content, while the internal friction angle decreases accordingly.2.In construction of the test section in Xiuning tunnel exit zone, 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 lining, etc. Field monitoring results show that, mylonitic rocks are strengthened after full-face grouting ahead and the rock level improves. It can see veins and cloumns of seriflux obviously after excavation. The deformations of tunnel face and surrounding rocks are within the allowable range and the forced state of support structure is in good condition.3.The construction process of the tunnel is simulated using finite element software MIDAS/GTS, which takes into account reinforcement the rock ahead and not reinforcement the rock ahead. 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 reduce after mylonitic rocks are reinforced ahead, the force of support structure is also been greatly improved.4.Comparing the field monitoring results with the numerical results it is found that good agreement between them. Comprehensive analysis shows that the effect of grouting of the test section in Xiuning tunnel exit zone is effective. It has improved the engineering properties and the stability of mylonitic rocks effectively, reduced the deformation of support and rock and improved the forced state of support structure. This study shows that reinforce the surrounding rock by full-face grouting ahead and seven-step three-stage excavation method can be used for the construction of Xiuning tunnel exit zone. It can make the tunnel excavation safety and quick.