高拱坝稳定综合法试验中坝肩软弱结构强度弱化效应研究

Comprehensive geomechanical model test can simulate factors affecting stability of high arch dams simultaneously including water pressure overloading of dam upstream face and strength reduction of weak structural planes. Therefore, it is one of the main methods to study the overall stability of high arch dams. However, subject to thousands tons of water pressure and long-term effect of complex seepage field during impounding and operation of a high arch dam project, what is the amount of the strength parameter reduction of the weak structural planes in the dam abutment? And how to reasonably choose the reduced strength value in the comprehensive geomechanical model test for evaluating the overall stability of high arch dam? They are the key problems influencing the application and popularization of the comprehensive geomechanical model test. This project will carry out in-depth research in combination with practical projects. First, through a series of water-rock coupling triaxial test, the strength weakening effect of weak structures in dam abutment under the coupled influence of seepage field and stress field will be revealed quantitatively. The weakening rates of the strength parameters will be obtained. And the mathematic expressions of the weakening laws will be deduced through theoretical analyses. The results can be served as the basis for the determination of the strength reduction amplitude of the weak structural plane for the model test. Then, according to engineering operation conditions, a reasonably strength reduction amplitude for the comprehensive geomechanical model test will be determined. Finally, a series of comprehensive geomechanical model tests and numerical simulations will be conducted, and the impact of different strength reduction schemes on the model test results will be analyzed. The main goals of the project are to strengthen the scientific basis of the comprehensive geomechanical model test, to improve and develop the test method, and to guarantee reliability of the model test results.

地质力学模型综合法试验可以同时模拟大坝上游的超载和坝肩坝基软弱结构强度降低等影响高拱坝稳定的多种因素，是研究高拱坝整体稳定的重要方法之一。然而，大坝蓄水运行后，坝肩软弱结构面在上千万吨的水荷载以及复杂的渗流场作用下，其强度参数究竟弱化多少？模型试验中结构面降强幅度又如何取值？是困扰综合法试验应用和推广的关键问题。本项目结合实际工程，首先通过水岩耦合三轴压缩试验，定量地揭示典型高拱坝工程在运行条件下，坝肩软弱结构在应力场、渗流场耦合作用下强度参数的弱化效应，获得相应的弱化率，并通过理论分析推求弱化规律的数学表达式，为高拱坝整体稳定模型试验提供结构面降强幅度的依据。然后根据工程运行条件，确定综合法试验中合理的降强幅度。最后通过地质力学模型试验和数值模拟，分析不同的降强方案对综合法试验成果的影响。研究成果为地质力学模型综合法试验的完善和发展奠定基础，为模型试验成果的可靠性提供保障。

高拱坝工程蓄水运行后，在上千万吨的水荷载以及复杂的渗流场长期作用下，坝肩坝基软弱结构的弱化效应是影响高拱坝工程长期安全稳定运行的关键问题之一。其难点在于如何定量地揭示这种弱化效应，并且在高拱坝长期运行安全评价中合理的模拟这种弱化效应。本项目在前期研究工作的基础上，采用试验研究、理论分析、数值模拟等方法，对上述关键问题进行了系统的研究，取得的主要成果包括：（1）提出了坝肩软弱结构水岩耦合弱化率测试方法，开展了典型高拱坝工程坝肩软弱结构水岩耦合弱化试验，定量揭示了坝肩软弱岩体的弱化特性和水压效应、围压效应及时间效应；（2）开展了高拱坝工程坝肩软弱结构力学参数弱化规律研究，建立了基于水岩耦合作用下的强度参数预测模型；（3）开展了地质力学模型综合法试验中降强幅度研究，确定了锦屏一级拱坝各主要结构面的弱化率，为拱坝的长期运行稳定性评价研究提供参考；（4）进行了不同降强方案对高拱坝坝肩稳定模型试验成果的影响研究，采用差值对比及单因素方差分析法比较分区降强和统一降强两方案的合理性，得出分区降强方案差值小且与现场监测资料无显著性差异因而较优的结论；（5）基于实测资料和参数预测模型开展了锦屏拱坝长期稳定安全性分析，评价了锦屏拱坝的长期稳定性。开展了锦屏一级拱坝典型高程拱圈分区降强的综合法地质力学模型试验，得到坝与地基稳定强度储备系数K1=1.08~1.14，超载系数K2＝3.3~3.6，综合稳定安全度Kc＝3.6~4.1。采用分层分区降强方案开展三维数值计算，得到在运行条件下，坝与地基整体稳定强度储备系数K1=1.2~1.5，超载系数K2＝4.0，综合稳定安全度Kc＝4.8~6.0，评价了运行期拱坝整体稳定安全性。通过本项目的研究，使地质力学模型综合法试验更能真实反映工程实际情况，对高拱坝工程的整体稳定安全性做出更加合理的评价。同时本项目的研究成果可推广应用在高边坡、地下洞室等其它工程的模型试验研究中，为这些工程的稳定性研究提供新的途径。