Study On The Construction Effects And Technical Parameters Of Loess Tunnel Steps Method

Step method can affect surrounding rocks less when tunneling, so it is in favor of rocks stability and mechanized operations. Because of good adaptability, easy method conversion, construction organization and security control, step method should still be mainstream of railway tunnel construction method s in some period. But now the standard of loess tunnel construction using step method is not comprehensive and detailed. Aiming at this situation, my artical works at statistical analysis of Bao Lan tunnel and tunnel numerical simulations about construction technical parameters such as step length, step height, the distance between invert and working face. It is also committed to excavation process optimization and support measures simulation. In the end, my article gets some law about initial support displacement, the maximum and minimum stress of initial support and the displacement of working face and it also provides recommended values of construction technical parameters.(1)By counting physical and mechanical parameters of loess and step method technical parameters, my artical gets the statistical values of the parameters and the relationship of different statistical values.(2)By analysising the simulation results of working conditions of different step lengths and heights, my article gets the law of step length and height’s effects on tunneling in different moisture situations and gives the recommended values of step length and height.(3)By analysising the simulation results of different sizes of core soil, my article gets that the core soil can contro l tunnel working face deformation well. And the bigger core soil size is, the more obvious the effect is. The recommended core soil size is that: height is about 2 meters, width is 1/3 to 1/2 of the tunnel’s width, length is about 3 to 4 meters.(4)By analysising three kinds of excavation processes, my article gets that: excavating middle part first and then staggered excavation of both sides is better than staggered excavation of both sides, staggered excavation of both sides is better than just excavation of middle part first.The three kinds of methods’ technical parameters are that: to the three, the core soil is about 5 meters. To the first, staggered distance of middle step is 3 to 4 meters and of below step is 4 to 6 meters. To the second, staggered distance of middle step is 2 to 4 meters and of below step is about 2 meters. To the third, the distance in advance of middle step is 2 to 4 meters and of below step is 4 to 6 meters.(5)Forepole can control vault sinking well. Forepole and temporary inverted arch can control convergence, the max and min stress and the surrounding rock’s max plastic strain. The auxiliary measures’ technical parameters are that: the length of forepole is 4 to 5 meters.