| It has been a focus of debate for a long time how the system bolts act in the loess tunnel. At present there are two viewpoints, one view is that the bolts in the arch of the loess tunnel don't have effect on the Loess stability of the tunnel, so the bolts need not set in the anchor; Another view is that it should set bolts in the anchor, because the bolts play a key role in the anchor stability of the loess tunnel. This situation not only brings great difficulties to the Loess tunnel design, but also causes the construction support of the Loess Tunnel confused. 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 Hanguguan Tunnel as our experimental section in which we set system bolt section for 45 meters and non-system bolt section for 42 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 result indicate: both the two sections has almost the same settlement in the tunnel crown and the section with system bolt section has a little more 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. 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 and cost.
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