The Analysis On Mechanism Of System Rockbolts For The Flat And Large Cross-section Expressway Tunnel

At present, the anchor technology has already became the most economical and effective methods to enhance stability of the geotechnical engineering,and it has been already applied widely in geotechnical engineering domain, like slope engineering, runnel engineering and building foundation ditch and so on. However, it is still not completely clear for the anchoring mechanism of bolts. There has been a debate on the effect of system rockbolts for tunnel structure. Currently, there are two major academic perspectives: one is that the system rockbolts are non-functional for the stability of tunnel, so they can be lifted; another is that the system rockbolts are the key to the stability of tunnels, so they should be set up. The debate has not only brought great distress to the tunnel design, but also caused confusion to the tunnel construction.The paper sets in the on-site monitoring and measuring for the second phase project of Zhangjiakou-Shijiazhuang expressway tunnels. First, through the on-site measuring data analysis, it evaluates the actual effect of the system rockbolts in the tunnel system under different rock conditions. Then, with the numerical simulation software for the geotechnical engineering analysis - FLAC3D, it simulates the flat and large cross-section expressway runnel construction process in different rock conditions and under different programs of the system rockbolts. By analysing the numerical simulation data of the rock displacement, bolt axial force, the stress in the tunnel primary liner, the stress in tunnel secondary liner, and plastic zone of surrounding rock etc, this essay evaluates system rockbolts' effect, and analyzes its mechanism. Finally, based on an analysis of these results to optimize design parameters of system rockbolts of the flat and large cross-section expressway tunnel, we can draw reference for similar tunnels' system rockbolts design and construction.