大断面浅埋黄土隧道锚杆作用效果的试验研究

黄土隧道系统锚杆的作用效果问题一直是争论的焦点。结合正在修建的郑州-西安铁路客运专线大断面黄土隧道，采用现场对比试验方法对系统锚杆作用效果进行研究。为了使试验结果有可比性，选取试验条件基本相同的贺家庄隧道洞身段作为试验段，分别设置有系统锚杆段40 m和无系统锚杆段40 m。对比试验的内容包括：拱顶下沉、拱脚下沉、水平收敛、围岩压力、初支钢架应力、锚杆轴力等。试验结果表明，有系统锚杆段比无系统锚杆段的拱顶沉降大40 %左右、水平收敛大25 %左右，两者的土压力和钢架应力相差不大；锚杆轴力较小，且拱部受压。经综合分析认为，拱部锚杆的支护效果不明显，取消拱部锚杆可减少施工工序，加快隧道初期支护断面及早封闭，能更好地控制支护沉降与变形，并节约工程投资。

Experimental study on bolt effect on large section shallow depth loess tunnels

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.