滇中引水工程香炉山隧洞地应力特征及其活动构造响应

In-situ stress characteristics and active tectonic response of Xianglushan tunnel of Middle Yunnan Water Diversion Project

滇中引水工程香炉山隧洞埋深大、距离长且处于复杂的构造地质环境中。为查明其地应力分布特征,统计分析了隧洞沿线10个钻孔的水压致裂法地应力测试成果。3个主应力关系主要表现为SH>SV>Sh,反映了隧洞沿线以走滑性质为主的构造特征。工程区浅部地层的应力大小主要受地层岩性与断裂带影响。一方面坚硬岩体的水平主应力明显大于软质岩体;另一方面断裂带的发育致使隧洞沿线的应力水平相对较低,同时断裂带局部区间力学性质的差异导致浅部地层水平主应力呈现出较大离散性。香炉山隧洞最大水平主应力的测试方向主要分布在NNE-NEE向,与隧洞沿线一系列全新世活动断裂走向及区域构造主压应力方向趋于一致,响应了研究区震源机制解特征和楔形块体的运动特征。基于实测应力数据和断层滑动理论,隧洞沿线活动断裂目前处于相对稳定状态,而鹤庆-洱源断裂更为接近断层滑动的临界条件,随着应力的不断积累其稳定性情况值得进一步关注。

Xianglushan tunnel of Middle Yunnan Water Diversion Project is a deep buried and long distance tunnel in the complex tectonic geological environment.In order to find out the distribution characteristics of in-situ stress,the results of measured stress by hydraulic fracturing method in 10 boreholes along the tunnel are statistically analyzed.The three principal stress relationships are mainly expressed as SH>SV>Sh,which accords with the strike-slip tectonic characteristics along the tunnel.The in-situ stress of shallow stratum in the project area is mainly affected by the lithology and faults.On the one hand,the horizontal principal stress of hard rock mass is obviously greater than that of soft rock mass.On the other hand,the stress level along the tunnel is relatively lower due to the development of faults.Meanwhile,the difference of mechanical properties in the local section of fault zones makes the horizontal principal stress in shallow stratum discrete.The maximum horizontal principal stress direction of Xianglushan tunnel is distributed in NNE~NEE direction.And it is almost parallel to the strike of a series of Holocene active faults along the tunnel and the direction of regional tectonic principal compressive stress,which is in response to the characteristics of focal mechanism solution and wedge block movement in the study area.Based on the measured stress data and the fault slip theory,the active faults along Xianglushan tunnel are in a relatively stable state at present.Among them,Heqing-Eryuan fault is closer to the critical condition of fault sliding.Therefore,with the accumulation of stress in fault zone,the stability of Heqing-Eryuan fault deserves further attention.