Characteristics of in-situ stress field and fuzzy comprehensive evaluation of the influence of active faults on the water diversion engineering of Xianglushan Tunnel Area in central Yunnan

In-situ stress testing of eight boreholes by hydraulic fracturing was carried out at the active fault zone of Xianglushan Tunnel engineering area of water diversion project in central Yunnan. The results show that the horizontal tectonic stress plays a dominant role in engineering area. The stress regimes in Longpan-Qiaohou Fault and Lijiang-Jianchuan Fault area are of strike-slip faulting. The stress regimes in west branch and south segment of Heqing-Eryuan Fault area are strike-slip and reverse faulting, respectively. From the standpoint of stress accumulation, the measured maximum principal stresses at most test points of the three active faults within the detection range do not exceed the thresholds that cause the slipping instability of the fault. There is a difference between the dominant direction NNE-NE of the measured maximum horizontal principal stresses obtained by in-situ stress test and the NEE direction of the principal compressive stress of the current tectonic stress field obtained from the inversion of focal mechanismin this area, indicating that the measured in-situ stresses have been influenced to a certain extent by fault activities. Taking account of multiple index parameters of active fault deformation and mechanical properties, the Fuzzy-Grey comprehensive evaluation of the influence of active faults shows that the influence of Longpan-Qiaohou fault on tunnel engineering is weak and Lijiang-Jianchuan Fault is the strongest, which should arouse more attention.