陕南特长公路隧道水压致裂法地应力测量结果及工程地质意义分析

中国西部地区地势复杂，区域构造应力场各向异性显著，了解地区地壳应力状态是判断隧道设计阶段线路布设合理性的基础，也是预测隧道施工过程可能出现岩爆、断层滑动等其他工程灾害的重要参数。为了研究陕南特长高速公路隧道现今地应力状态，基于古仙洞隧道钻孔(ZK10钻孔)与化龙山隧道钻孔(ZK11钻孔)水压致裂地应力测量，获得了两隧道现今地应力分布特征。古仙洞和化龙山特长深埋隧道最大埋深处S_H值分别为13 MPa和22 MPa；古仙洞与化龙山隧道的应力关系分别为S_H>S_h>S_v和S_H>S_v>S_h，水平主应力起主导作用；S_H方向为近北西—北西西向，与区域现今构造活动背景基本一致，主要受秦岭造山带活动断裂影响。基于地应力测量结果、相关理论及判断依据认为:最大水平主应力方向与洞轴线夹角，有利于隧道围岩稳定，研究区内古仙洞与化龙山隧道的总体布置是合理的；采用岩石强度应力比法、陶振宇判据、Russenes判据和岩石应力强度比法综合判定研究区内两隧道不具备发生中等强度以上等级岩爆的可能；利用莫尔-库伦准则及拜尔定律，摩擦系数μ取0.6~1.0，对研究区内两隧道的现今地应力状态分析后发现，两隧道附近断裂带的地应力大小未达到地壳浅部断层产生滑动失稳的临界条件，处于较稳定的应力状态。 

Study on the hydraulic fracturing in-situ stress measurement in super-long highway tunnels in southern Shaanxi:Engineering geological significance

The complex terrain and marked anisotropy of regional tectonic stress field in western China make the crustal stress state an important assessment parameter. Understanding the regional crustal stress state lays the foundation for assessing the layout at the tunnel design stage and predicting rockburst, fault slip and other engineering disasters in the tunnel construction process. This study aims to explore the current in-situ stress state of the super-long highway tunnels in southern Shaanxi. We did hydraulic fracturing in-situ stress measurement of the Boreholes ZK10 and ZK11 in the Guxiandong tunnel and the Hualongshan tunnel, respectively, and thus characterized the current in-situ stress distribution of the two tunnels. The measurement results show that:The S_H values at the maximum buried depths of the Guxiandong and Hualongshan super-long deep tunnels are 13 MPa and 22 MPa, respectively. The stress relations of the Guxiandong and Hualongshan tunnels are S_H>S_h>S_v and S_H>S_v>S_h, respectively, and horizontal principal stress plays a leading role. The S_H direction is NW-NWW, which is basically consistent with the direction of the maximum principal stress in the basic database of crustal stress environment in mainland China. Three conclusions were drawn from the results of in-situ stress measurement in combination with related theories and assessment criteria. Firstly, the angle between the direction of maximum horizontal principal stress and tunnel axis is beneficial to the stability of tunnel surrounding rocks. The overall layout of the two tunnels is reasonable. Secondly, rock burst with moderate strength or above will not occur in the two tunnels according to a comprehensive study using the rock strength-stress ratio method, Tao Zhenyu criterion, Russenes criterion and rock stress-strength ratio method. Thirdly we used Mohr-Coulomb criterion and Bayer's law, let the friction coefficient μ have the value between 0.6~1.0, and then we analyzed the present stress state of the two tunnels. It is found that the stress of the fault zone near the two tunnels did not reach the critical condition of sliding instability of shallow faults in the crust, while it is in a stable stress state.