川西折多山某深埋隧道地应力测量及其应用研究

川西地区地质构造环境复杂,该区深埋隧道建设过程中经常面临岩爆风险,而地应力条件对深埋隧道的规划建设和岩爆风险预判具有重要意义。本研究利用水压致裂法在川西折多山某深埋隧道开展了原地应力测量及其工程效应分析。某钻孔196~650 m深度范围内的地应力测试结果显示,隧址区以水平构造应力为主导,测试深度范围内水平主应力随深度线性增加,且应力增加梯度高于中国大陆背景值。地应力结构整体以逆断型(S_H>S_h>S_v)为主,其中389.50~560.50 m深度范围属应力释放区,地应力结构以走滑型(S_H>S_v>S_h)为主。侧压系数及最大、最小水平主应力比值随深度分布基本符合中国大陆各参数变化特征。最大水平主应力方向为NWW向,与区域应力场分布及周边活动断裂反映的力学机制一致,主要受印度板块向欧亚板块持续俯冲和高原物质东南向扩散作用控制。测点现今地应力强度较高,临近断裂失稳状态,随着应力的不断积累,区内优势破裂方向或已有断裂的特殊构造部位可能发生失稳滑动。最后,基于地应力测量结果对深埋隧道围岩稳定性进行了预判分析,受隧址区高地应力影响,围岩发生中-强岩爆的可能性较大,需优化设计并重点防护。

In-situ Stress Measurement and Its Application of a Deep-buried Tunnel in Zheduo Mountain,West Sichuan

Characteristics of present stress state at a deep-buried tunnel in Zheduo Mountain(west Sichuan)are analyzed based on in-situ stress measurement results at 196-650 m depths using the hydraulic fracturing me-thod.The measured results show that the stress state is dominated by horizontal principal stress,which increases linearly with depth and with higher gradient than the Chinese mainland background value.Reverse stress regime(S_H>S_h>S_v)is dominant overall within the measurement depth.The stress-release zone is at 389.50-560.50 m depth,and the stress regime is mainly strike-slip with relative principal stress magnitude of S_H>S_v>S_h.The lateral pressure coefficients and the ratio of maximum and minimum horizontal principal stress corresponds approximately with the variation characteristics of Chinese mainland.The fracture impression results reveal that the maximum horizontal principal stress is predominantly WNW,consistent with the regional stress field and mechanical mechanism reflected by the surrounding active faults.Stress field in the study area is mainly controlled by the ongoing India-Asia continent-continent collision and the compressive tectonics from the growing Tibetan Plateau onto the rigid Sichuan Basin.The test borehole is nearly critically stressed in the current stress state.The optimal-orientated plane or special section of the exiting faults may experience instability sliding with the continuous stress accumulation.Subsequently,tunnel stability from the in-situ stress perspective is discussed.The results reveal that the deep-buried tunnel favors medium-strong rock-burst due to strong in-situ stress state and deep burial,and the optimized design and constructive protection should be focused.