大岗山水电站地下厂房区初始地应力场Nelder-Mead优化反演研究

Nelder-Mead algorithm for inversion analysis of in-situ stress field of underground powerhouse area of Dagangshan Hydropower Station

初始地应力是大型地下洞室群设计与施工所要考虑的重要因素之一。结合大岗山水电站工程地质条件以及实测地应力资料,分析了地下厂房区初始地应力的影响因素,建立了基于侧压力系数的三维地应力反演模型,提出Nelder-Mead法与有限元联合反演法,将有限元程序作为一个单独模块嵌入到Nelder-Mead算法程序中,对建立的地质概化模型进行计算,以实测点地应力值与计算应力值建立精确罚函数误差模型,进行优化逼近分析。通过实测点的计算应力值与现场实测值的比较,从而获得地下厂房区初始地应力场较为合理的分布规律,为水电站开挖模拟及长期稳定性分析提供了合理的初始条件。

The in-situ stress is one of the most important factors for the design and construction of large scale underground structure group. Based on the engineering geologic characteristics and the measured data of in-situ stress in the region of Dagangshan Hydropower Station, the lateral earth pressure coefficient model for 3-D in-situ stress inversion is established taking into account the influencing factor of in-situ stress. A methodology of inversion analysis combining the Nelder-Mead algorithm and finite element method is proposed, in which the finite element program is embedded as a module in the Nelder-Mead algorithm. Then, a new exact penalty error model is established between the actually measures and corresponding calculated results of stresses. Through the finite element approximation analysis, the optimum inversion coefficient can be derived. Through the comparison between calculated and measured stresses of measuring points, it is shown that the calculated stresses are similar with the measured stresses, which suggests that the reasonability of in-situ stress field finite element approximation. Therefore, the calculated stress field can be used for the analysis of the excavation simulation and long-term stability of Dagangshan Hydropower Station.