考虑地应力分布形式的坝址区初始应力场二次反演方法

在建的乌东德水电站区域构造运动强烈，断层、褶皱及节理较为发育，加之河谷纵横、沟谷深切，导致该区域岩体地应力分布极为复杂，非线性特征显著。为准确获取坝址区初始地应力场的分布特征，通过对地应力分布形式进行优化，提出了考虑地应力张量分布特征的岩体应力场二次反演方法。首先，将地应力张量分解成自重应力、构造应力及非线性应力3个部分，同时依据坝址区地形地貌、地质构造及非均匀性岩层等因素，构建FLAC3D计算模型，利用叠加法原理对坝址区初始地应力场进行一次反演。然后，主要考虑坝址区附近小规模构造及局部开挖条件的影响，构建三维离散元（3DEC）精细模型，同时从一次反演中提取精细模型的初始地应力侧压系数和自重修正系数，并利用均匀设计法进行优化，对精细模型进行二次反演。研究结果表明：一次反演计算获得的初始应力场整体上与实际情况吻合较好，但在局部构造附近与实测值相差较大；二次反演考虑局部地质构造及开挖条件的影响，同时结合一次反演的计算成果，各测点的应力计算值与实测值基本一致；通过将大型商业软件FLAC3D和3DEC相结合来反演复杂条件下工程区初始应力场，在一定程度上实现了岩体应力场在大范围内整体连续、小范围内受局部地质构造等影响导致不连续分布的特点。该研究方法可为类似工程提供借鉴。

Two-stage back analysis method of initial geostress field in dam areas considering distribution characteristics of geostress

The Wudongde hydropower plant under construction is located where there exists strong regional tectonic movement. Faults, folds and joints are well developed, and most of the river valleys are steep and narrow in this area. Therefore, the distribution characteristic of geostress is quite complex, which exhibits a significant nonlinearity. To accurately obtain the distribution rule of initial geostress field in the dam area, a new two-stage back analysis method is presented, which considers the optimized distribution characteristics of geostress. Firstly, the geostress is decomposed into three components including gravitational stress, tectonic stress and nonlinear stress. By considering the influence of topography, geological structure, and inhomogeneity of the rock mass, a model in numerical software FLAC3D is developed. The superposition method is applied to the first-stage back analysis of initial geostress field. Then, by considering the small scale geological structures and local excavation in the vicinity of the dam area, a refined three-dimensional discrete element model using 3DEC is established. The preliminary lateral pressure coefficient and gravitational stress modified coefficient of the refined model are obtained from the developed model. Moreover, the calculation for the second-stage back analysis of geostress field is conducted by optimizing the coefficients based on a uniform design. During the first-stage back analysis, the calculated results agree well with the measured data on the whole, but the difference between them is large in the vicinity of the local geological structures. The calculated results are in agreement with measured data in the second-stage back analysis by considering the small scale geological structures, local excavation and the results in the first-stage back analysis. The commercial FLAC3D and 3DEC software can be combined to obtain the initial geostress field under complex conditions. The distribution characteristics of geostress field shows continuous in a large scale and discontinuous within a small range due to local geological structures.