Huge underground caverns design and excavation: interpretation of monitoring data through back-analyses.

Nowadays in conjunction with the tremendous demand for electricity which is the backbone of the new civilization. Humanity searches for renewable and sustainable resources of electric energy and invests a lot of money to find modern solutions. Thus, one of the innovative technologies in the new era is the power pumped-storage hydroelectric plants underground. in addition to that the superb latest technologies not only generate electricity from these hydropower plants but restore the excess energy that already exists on the grid. So, these hydropower plants act as large batteries. Also, these plants have less cost, less environmental harm, no greenhouse gases emission, and their life cycle has around 40-50 years. The research is a discussion about a hydropower plant that is located 300 meters below the ground surface in the complexity of geological conditions, heterogeneity, and anisotropy of the rock mass. the storage capacity of water that will be in the upper and lower reservoirs reach around three and half million cubic meters. The head between the upper and lower reservoirs will be around 450 m. The project consists of around 6 km of underground tunnels. Furthermore, two caverns that are 97m long, 18 meters wide, and 27 meters high. The purpose of the thesis is a scope on back-analysis of a huge underground caverns excavation of hydroelectric plant and interpretation of monitoring data. This study includes a back-analysis of the displacements that have been recorded by the extensometers and the recorded forces for the instrumented tendons and bar anchors of the caverns. In addition, a time-dependent analysis was executed to predict the performance of the rock mass which is located around the excavation contour, and the stability of the excavated structure over time. The analysis in this study was performed by using three-dimensional models in the finite element software RS3 (Rocscience,2021) and concerning modeling was made by Rhino 7(Rhinoceros,2021). The analysis was based on the latest geological model and the mapping information that was obtained during excavation. Furthermore, the results were compared and emulated with the results received from FLAC3D (Itasca,2020) with equivalent geomechanically and in situ stress parameters. Thanks to the process of the back-analysis and the evaluation of the performance of the excavated structure, reached outcomes can be used as a handling tool in prediction procedure to foretell the creep behavior, time dependence of the rock mass, and the stability of the hydropower plant over the life cycle of the project.