高地应力地区围岩劈裂破坏现场监测和能量耗散模型及应用

随着计算机的发展，数值模拟等技术在岩土领域的应用也越来越广泛。在进行埋深较大的地下洞室施工时，由于岩体的脆性特征，在高地应力作用下，洞室围岩容易出现劈裂破坏。因此，在深部岩体开挖过程中，对于围岩的劈裂破坏区域的预测格外重要。但是目前在现有的计算模型中，尚没有能够很好描述劈裂破坏特性的有限差分本构模型。本文从能量耗散原理出发，结合了横观各向同性模型，采用劈裂破坏准则对模型单元应力状态进行判断，利用FLACE3D的二次开发功能，在C++的编译环境下对模型进行如下改进，在原有模型中导入能量耗散理论和加卸载判据，得到新的自定义横观各向同性计算模型。该模型可以判断岩体所处的加卸载状态，并根据岩石状态使用不同的力学参数进行计算，并且还能够描述高地应力地区围岩产生竖向劈裂裂纹后，不同方向上围岩的不同力学性质。在此基础上对大岗山水电站大型地下洞室群开挖过程中的稳定性进行了计算。另一方面，在大岗山水电站大型地下洞室群开挖工程现场开展了洞周围岩劈裂破坏区的监测，采用钻孔电视、滑动测微计以及形变电阻率三种观测方法，测得了主厂房在进行各个开挖步开挖时，主厂房与主变室之间岩桥中围岩的位移以及劈裂破坏的情况。之后，将现场监测结果与不同本构模型的稳定性分析的计算结果进行对比。并得到以下结论：根据监测结果，大岗山水电站地下洞室群在进行开挖时，主厂房下游边墙围岩的劈裂区平均深度约为13~15m，考虑能量耗散的横观各向同性模型计算所得主厂房下游边墙劈裂区平均深度约为13.6m，二者十分接近；主厂房洞室在进行开挖施工后，随着与临空面的距离增加，围岩内部关键点的位移逐渐减小，在靠近主变室边墙附近，由于又形成了新的劈裂破坏区，因此围岩关键点位移又逐渐增加，考虑能量耗散的横观各向同性模型可以较好的反应围岩位移变化趋势，与监测曲线吻合度较高，而使用摩尔库伦模型以及横观各向同性模型计算得到的曲线则与监测曲线有较大区别；根据稳定性分析结果，主厂房下游边墙吊车梁位置关键点和主厂房洞中关键点开挖后洞壁出现的位移较大，其最大水平位移为29.46mm。主厂房拱顶在开挖的初期位移较大，拱顶竖直位移最大值为10.58mm。主变室拱顶竖直位移为10.06mm。结果表明，对比其他现有的有限差分模型，考虑能量耗散的横观各向同性模型计算结果与实际监测值最接近，可以反应不同开挖步时，围岩内部关键点位移的变化趋势。因此在高地应力地区地下洞室开挖时，可以使用该模型对洞周围岩的劈裂区进行计算与预测，以及在洞室开挖完成后对洞室围岩的稳定性进行分析，并参考计算结果对关键区域加强监测与管理，从而减小围岩劈裂破坏对洞室稳定性的影响。

Splitting Failure on Side Walls of Underground Cavern in High In-situ Stress Area and Applications of an Energy Dissipation Model

With the development of computer, the application of numerical simulation technology in geotechnical field is more and more extensive. In the construction of deep buried underground cavern, due to high in-situ stress and brittleness of rock mass, the surrounding rock mass of underground caverns are prone to appear splitting failure. Therefore, in the process of deep rock excavation, the prediction of the splitting failure zone of surrounding rock is particularly important. However, there is no FDTD model which can well describe the splitting failure characteristics in the existing calculation models. In this paper, based on the energy dissipation principle, combined with a transversely isotropic model, judged by the splitting failure criterion of model element stress state, after using the secondary exploration of the FLAC3D in the C++ compiler environment, a kind of new custom transverse isotropic calculation model is obtained. This model could determine the rock mass loading-unloading state, and according to the state of rock using different mechanical parameters when it is calculated, and also could describe the different mechanical properties of surrounding rock in different directions when the surrounding rock mass in the high geostress area produce the vertical cracks. Using this new custom model, the stability of excavation of large underground caverns in Dagangshan hydropower station is calculated. Besides, the displacement and the entire process of rock splitting failure of each excavation steps of the main house have been achieved through monitoring on side walls of the construction site of large-scale caverns in Dagangshan via borehole TV, micro sliding extensometer and deformation resistivity instrument. Then, the results of field monitoring are compared with the calculated results of the stability analysis of different constitutive models , and the following conclusions are obtained: According to the monitoring results of Dagangshan Hydropower Station underground caverns during the excavation, the average depth of splitting zone of the sidewall in the main power house is about 13~15m, while the average depth of the same area obtained by the calculation based on the new model is about 13.6m. The two results are very close to each other; After the excavation of the main power house, the displacement of the key points in the surrounding rock gradually decreases with the increase of the distance from the free surface. While in the vicinity of the side wall of the main transformer chamber, a new splitting failure zone is formed, so the displacement of key points of surrounding rock gradually increases. The new model can reflect the change trend of surrounding rock displacement better than the others. According to the results of the stability analysis, the key point displacement of the downstream side wall and the position near the crane beam of the main power house is larger, the maximum horizontal displacement of the sidewall is 29.46mm. The vault displacement of the main powerhouse is larger in the initial stage of excavation, and the maximum vertical displacement of the vault is 10.58mm. The results show that, compared with other existing FDTD model, calculation results by the new custom model is close to the actual monitoring value, which could reflect the displacement of the surrounding rock mass in different excavation step and the change trend of the surrounding rock displacements of the key points. This new model could be used in calculating and predicting the splitting zone of the surrounding rock when the underground cavity in high geostrese areas during excavation and also could be used in stability analysis on the surrounding rock after excavation, or referenced to strengthen the monitoring and management of key areas, so as to reduce the splitting failure effect on tunnel stability.