Study Of Undercrossing Construction Technology For Xiuning Tunnel Under The Longtan Reservoir

The pape is based on the construction project of Xiuning tunnel under the Long tan reservoir in the Guangkun railway line. By using theoretical analysis, a series of laboratory tests and numerical analysis, the paper has studied the construction technology of tunnel undercrossing a reservoir. The main contents and conclusions are as follows:1. After a series of laboratory tests, the paper has a summary of changing rule of the Elastic modulus, Internal friction angle, cohesive force following the moisture content, and of the coefficient of permeability following dry density. The results show that elastic modulus, internal friction angle reduce but cohesive force Increase with the Moisture content Increasing, and that the coefficient of permeability Increase with the dry density reducing.2. The paper has designing then level vacuum pumping plan, combining the laboratory tests result and the level vacuum pumping plan, a numerical analysis is carried out by using fluid solid coupling method. The result shows that, the distribution of pore pressure is the same under different coefficient of permeability and same degree of vacuum, and also that the reinforcement effect increase with the degree of vacuum increasing. The result also show that the changing of Elastic modulus, Internal friction angle, cohesive force coefficient of permeability,is less than12%, due to the initial value is low, the level vacuum pumping can’t achieve the goal to improve the grade of surrounding rock and soil.3.After learning the plan of Xiuning tunnel to construct under crossing the Longtan resevoir,the paper has a study of the full section grouting method by using numerical analysis.The result shows that the grouting zone can plug the water and restrain the deformation as better as the grouting effect.The paper also has a study to have a assessment on the the three step method with full section grouting,the result shows that the plan can achieve the goal of plugging water and restricting the deformation compared with the three step method without full section grouting.