Study On Supporting Characteristic Of Tunnel Feet-lock Bolt (Pipe) In Weak Surrounding Rock

With the increasing of tunnels in weak surrounding rocks, the application of feet-lock bolt (pipe) in controlling great deformation of tunnel is more and more extensive. For the sake of knowing supporting characteristic of feet-lock bolt (pipe) in weak surrounding rocks and providing theoretical basis for feet-lock bolt (pipe) design and construction, with theoretical analysis, numerical computation and field monitoring method, this paper studies the function mechanism and bearing characteristic of feet-lock bolt (pipe), gives supporting design and construction method of feet-lock bolt (pipe) in tunnels in weak surrounding rocks, and studies the application effect of feet-lock bolt (pipe) in tunnels. The main research contents and results are as follows:(1) Analyse the function mechanism of feet-lock bolt (pipe). Feet-lock bolt (pipe) plays a role through supporting, reinforcing surrounding rock similar to bolt, pre-support and grouting reinforcement, controlling tunnel deformation and improving stress condition of surrounding rock and supporting structure.(2) By means of numerical simulation, study bearing characteristic of feet-lock bolt (pipe) and analyse influence of different inserting angles, lengths, positions and diameters of feet-lock bolt (pipe) on tunnel deformation. The result shows that the reasonable angle inserting down of feet-lock bolt (pipe) is 0°～5°; within one length and diameter range, the effect of controlling tunnel deformation is more obvious with the length and diameter increasing; the reasonable position of feet-lock bolt (pipe) is 50cm above the arch and sidewall foot.(3) The design parameter table of tunnel feet-lock bolt (pipe) in weak surrounding rocks is given; it should attach much importance to the connection of feet-lock bolt (pipe) and primary lining and grouting effect by drilling grouting holes along the whole steel pipe during the construction process in order to improve supporting stiffness and intensity of surrounding rock around. Aiming at different diameters of feet-lock bolt (pipe), the construction method is given, insuring construction quality and exerting its supporting effect fully.(4) By means of numerical simulation and field monitoring, study the application of feet-lock bolt (pipe) in weak surrounding rock tunnels of IV-class in Baojiashan extra-long highway tunnel, V-class in Mingyazi tunnel and VI-class in Tianhengshan tunnel, and analyse the results of numerical simulation and field monitoring. On the whole, it shows that tunnel deformation is within allowable range; and feet-lock bolt (pipe) exerts its supporting effect to a great extent, and the results of numerical simulation and field monitoring are close. It indicates that the application effect of feet-lock bolt (pipe) in weak surrounding rock tunnels is obvious to a certain extent, and it also shows the validity of numerical computation.