南水北调西线工程坝区初始地应力场反演分析

依据南水北调西线工程阿达坝区工程地质条件以及实测地应力资料，采用多元线性回归分析理论以及FLAC3D计算程序，对建立的坝区三维地质概化模型进行计算，求出最优回归系数。对比回归计算值与现场实测值发现，二者量值相当且方向上接近，表明经过回归得到的地应力场是合理的，从而获得坝区较为准确的初始地应力场分布规律。进一步分析结果表明，(1) 谷底应力集中现象明显，应力集中区的垂直深度达80 m，应力峰值约为15 MPa；(2) 相距仅350 m 左右的两个钻孔，其最大水平主应力方向差异较大，反映出河谷区地形地貌对岩体应力方向强烈的控制作用；(3) 坝区为中等地应力区，在浅部以构造应力为主，随着埋深的增加，自重应力场控制作用逐渐增强。研究成果可为坝址及引水隧洞轴线布置的设计与施工提供重要依据。

Back analysis of initial geostress field of dam site in west route of South-to-North water transfer project

According to the site measurements of geostress and engineering geological conditions in Ada dam area of west route of South-to-North water transfer project, the established 3D simplified geological model of the dam is calculated by FLAC3D combined with the linear multivariate regression analysis principle. Then, the optimum regression coefficients have been achieved. Comparing the computed results with the measured geostress data, it is found that the two are very close in values and directions, which suggests the accuracy and reasonability of the geostress field regression. Therefore, the distribution rule of the initial in-situ stress field can be obtained accurately. The further analysis is shown as follows: (1) The stress concentration at the bottom of the river valley is obvious; and the vertical depth of the zone is about 80 m with the peak value of 15 MPa. (2) There exists considerable difference between the maximum horizontal principal stress direction of two boreholes which are only 350 m apart, which reflects the control action of the direction of compressive principal stress by geographical and topographic features of the river valleys. (3) The initial geostress field in dam area is a medium stress field which is dominated by tectonic stress field at the shallow parts; but control action of gravity field increases gradually with the increment of buried depth. The results above provide important reference for design and construction of Ada dam and its diversion tunnel axis layout.