天池坪隧道水压致裂法地应力测量及三维地应力场宏观扩展分析

天池坪隧道是兰渝铁路兰州至广元段的一座特长单线隧道,位于甘肃省宕昌县境内,全长14.528 km。选择4个测孔、26个试验段进行水压致裂地应力测量。天池坪隧道各测点的共同特征是现今应力场以水平应力为主导,应力量级属于极高应力水平。最大主应力方向为北北西-北西-北西西向,与宏观应力场方向吻合。 LY1测点的最大水平主应力方向为N40°W~N45°W,与隧道轴线方向夹角较大,对隧道围岩稳定不利。结合实际的地质条件和地层参数,在实测地应力结果的基础上,采用三维有限元多元回归分析方法,扩展分析隧道区域原始宏观地应力场。宏观地应力场的分析结果表明,隧道轴向位置的横向应力值大于10 MPa,横向侧压力系数处于1~2之间,且局部地段因地形等因素引起的应力集中而导致横向侧压力系数偏大。宏观地应力场的分析结果对工程设计与施工具有重要参考价值。

Geo-stress Measurement by Hydraulic Fracturing Method and 3-D FE Regression Analysis of Multivariate Geo-stress Field of Tianchiping Tunnel

Tianchiping tunnel is a very long single track tunnel from Lanzhou to Guangyuan of Lanyu railway, which is located at Tanchang couty of Gansu province. The total length of the tunnel is 14. 528 km. In the exploration area, a total of 26 hydrofracturing tests in 4 vertical exploration boreholes drilled from the ground surface are carried out. The results suggest that the present stress field of Tianchiping tunnel is dominated by horizontal stress, and the maximum horizontal stress is dominantly oriented NNW-NW-NWW. Stress magnitude is extreme high stress level. At the same time, the maximum horizontal stress orientations are closely consistent with those in the general contemporary stress field in southeast of Gansu Province. The maximum horizontal stress orientations in measurement hole No. LY1 is N40° W-N45°W. The angle is large between the maximum horizontal stress orientations and those along tunnel axis, which is a great disadvantage to the tunnel stability. Based on the geological conditions and rock mass properties, a 3D mechanical model is established, and the regional geo-stress field of tunnel area is analyzed by 3D multivariate FE regression from limited stress data of in-situ geo-stress measurement. The results of macro geo-stress field indicate that the transverse stress values are lager than 10 MPa along the tunnel axis,the lateral pressure coefficients is between 1 and 2,and stress concentration due to topography and other factors on local areas results to a great large lateral pressure coefficients. The results of macro geo-stress field are very important for dynamic design and construction.