Application Of Pre-cutting Method Of Tunnel In The Loess And The Analysis On Mechanics Of The Pre-cutting Structure

In this paper, the function of pre-cutting method in a loess tunnel is studied by the numerical simulation. Analysis of the applicability of the pre-cutting method in a loess tunnel was analysed by comparing the tunnel deformation and the mechanics of the pre-cutting structure. It provides a theoretical basis for the application of pre-cutting method of tunnel in the loess. The main work and research results are as follows:(1) The method of controlling the soft rock tunnel deformation was summarized. Attention should be paid to the function of the core rock at tunnel face in the tunnel deformation. Advance support, tunnel face, foot reinforcement are three aspects to strengthen the control of tunnel deformation.(2) Compared with the loess tunnel excavation method of whole section, using pre-cutting as advance support can effectively control the tunnel convergence, vault settlement and ground settlement, pre-cutting can reduce the pre deformation of tunnel convergence, but in the tunnel face of extrusion deformation control effect is limited.(3) From three aspects of the buried depth of the tunnel, supporting time, the excavation footage, the rule of tunnel deformation and the mechanics of the supporting structure are studied by using 20 cm and 25 cm thick pre-cutting. It should ensure the safety requirements of the supporting structure. The excavation of the tunnel should comply with the "digging fast, supporting fast" principle.(4) Parameters of reinforcement face fiberglass bolt (bolt length, bolt length of lap) is the key measure to control the tunnel face reinforcement effect, according to pre determine the scope of tunnel convergence deformation of bolt length, according to the working face to determine the length of bolt fracture surface of minimum length of lap; in the pre-cutting method, the feet lock bolt can not play the role of anchor.(5) According to the deformation law of tunnel face, the tunnel face reinforcement range can be optimized. When the reinforcement range is small, the face will occur large scale deformation. It is not conducive to the stability of working face. Using 8 m reinforcement range can meet the requirements.