南水北调西线工程区地应力测量及地应力场特征分析

STUDY ON IN-SITU STRESS MEASUREMENTS AND CHARACTERISTICS OF IN-SITU STRESS FIELD IN WEST ROUTE OF SOUTH-TO-NORTH WATER TRANSFER PROJECT

基于对南水北调西线一期工程场区现场水压致裂地应力测试工作,得出如下初步结论:(1)各线路孔中最大水平主应力值最高约为25 MPa,最大水平主应力方向均为NNE或NEE;(2)各坝址孔中最大水平主应力值最高约为17 MPa,最大水平主应力方向受局部地形地势影响变化较大,但大多数孔方向仍为NNE或NEE;(3)在试验深度范围内,线路孔侧压系数随着钻孔深度的增加逐渐减小;当测试深度在200 m以下时,侧压系数值基本维持在2左右;(4)各测孔侧压系数均大于1,表明工程场区地应力以构造应力为主导;(5)在测试深度范围内,各测孔的最大、最小水平主应力随岩层深度的增加均有增大趋势;(6)回归分析结果表明线路孔的最大水平主应力值随深度呈现良好的线性关系;(7)由于隧洞洞室埋深较深,且穿越高应力区,存在中等强度岩爆或流变的可能性。

The following preliminary results are obtained based on in-situ stress measurement in the west route area of South-to-North Water Transfer Project of China by using hydraulic fracturing （HF） method： （1） the largest amplitude of maximum horizontal principal stress in all the boreholes along the water transfer route is about 25 MPa with the orientation of NNE or NEE; （2） the largest amplitude of maximum horizontal principal stress is about 17 MPa in all the boreholes in the dams areas, and the orientations are mainly NNE or NEE though influenced by local topography： （3） the ratio of lateral pressure decreases with the increasing depth in all boreholes along the water transfer route. When the depth is greater than 200 m from the ground surface, the ratio is close to 2： （4） the ratios of lateral pressure in all boreholes are greater than 1, which implies that the tectonic stresses in this area are dominant; （5） the magnitudes of the maximum and minor horizontal principal stresses increase with the increasing depth of boreholes; （6） the fine linear relationship between the magnitude of maximum horizontal principal stress and borehole depth in all boreholes along the water transfer route is observed based on regression analysis： and （7） medium rock burst or rheology is likely to be induced by the high stress in the deeply buried, long tunnels.