Abstract: It has been a focus of debate for a long time how the system bolts act on the loess tunnel. Associating with the large section loess tunnel of the building Zhengzhou-Xi’an high-speed passenger rail lines, we have done many in site contrast testing to evaluate the effect of system bolt. For the good comparability of the testing result, we’d choose the tunnel which has the similar test condition. In this case, we take the Hejiazhang Tunnel as our experimental section in which we set system bolt section and non-system bolt section both for 40 meters. The main contrast experiences are the settlement of the tunnel crown and arch foot, horizontal convergence, surrounding rock pressure, the stress of initial supporting steel framework, axial force of bolt, etc. The testing results indicate: the section with system bolt has more 40% of the settlement in the tunnel crown and more 25 % horizontal convergence than the one without system bolt; there are little difference in the soil pressure and steel framework stress between the two sections; there is less axial force in the bolt and the part of arch is pressed. Through comprehensive analysis, we make the conclusion that there is little improvement of supporting effect in the crown bolt, so we suggest canceling the bolt to induce the construction procedure and quicken the enclosed of the initial supporting section of the tunnel. It will be helpful to control the supporting settlement and deformation and it also reduces the investment cost.

Key words: large cross section tunnel, tunnel in loess, bolt, contrast testing