中文摘要：

建立小湾水电站坝址区大范围有限元模型，考虑工程附近较大区域内的地形、地势和河流大转弯等因素，采用遗传算法与有限单元法相结合的联合反演方法，对坝址区初始地应力场进行一次反演；然后，考虑坝址区附近主要地质构造，建立坝基开挖松弛效应分析的小范围有限元模型，基于子模型方法，通过在一次反演模型中插值获得小范围模型的位移边界条件，对初始地应力场进行二次计算。研究结果表明：软弱地质构造对初始地应力场的反演有一定影响，一次反演中不连续结构面附近应力计算值与实测值相差较大；考虑软弱地质构造后的二次计算改善了一次反演所得的初始地应力场精度，大部分测点应力计算值更接近实测值，相对误差也逐渐减小，可将其应用于后续坝基开挖松弛效应分析中；反演结果同时也表明所采用的研究方法是可行的，对类似工程具有参考意义。

英文摘要：

The large-scale finite element model for dam site zone ofXiaowan Hydropower Station is established, in which the influences of topography and river turning are taken into consideration. The method combining genetic algorithm with finite element method is applied to the first-stage back analysis of initial geostress field at dam site zone. Then, the small-scale finite element model of dam foundation excavation and relaxation is established, considering the main soft geological structures in the vicinity of the dam site. Based on the sub-model method, the displacement boundary conditions of the small-scale model can be achieved by interpolating from the large-scale model of the first-stage back analysis, and calculation for the second-stage analysis of geostress field is conducted. Through comparative analysis, it is shown that the main soft geological structures have much effect on the results of initial geostress field, especially in the vicinity of discontinuity during the first-stage back analysis. And the precision of the initial geostress field in the first-stage back analysis has been greatly improved in the second-stage calculation. The geostress of most measuring points are much closer to measured values and the relative error has also been reduced gradually. So the initial geostress field after two-stage analysis can be used in the later analysis of relaxation effect during dam foundation excavation. And the results also indicate that the method is feasible and of great reference to similar projects.