Back-Analysis Research On Dagangshan Hydropower Station Construction Of Large Underground Caverns

With the implementation of the strategy of the Western Development, our country will plan and establish many large water conservancy and hydropower projects in the west in the next few years. It needs a lot of rock excavations underground concerning the hydropower station cavern construction, then the initial geostress and rock mechanics parameters are very crucial for the stability analysis of the surrounding rocks. Therefore, accurate simulation of the initial geostress and rational determination of rock mechanics parameters have very important engineering significance and application value.Dagangshan hydroelectric power station was selected as the engineering background of this paper, and inversion for the initial geostress field has been done based on systematic analysis. A displacement back analysis method to determine the rock mechanics parameters was set up, which has less calculation and high efficiency. It has resolved the inverse problem of the rock mechanics parameters during underground caverns effectively; meantime it has forecasted analysis for the stability of Dagangshan hydroelectric power station and supplied instructional suggestion for engineering design and construction. More specifically, this paper will discuss as below:1. Applying regression analysis and orthogonal polynomials fitting for the inversion of the Dagangshan underground initial geostress field, the hydropower initial geostress field and the corresponding fitting stress function have been obtained. The distribution and variation of the hydropower plant ground stress has been revealed by the inversion.2. A displacement back-analysis method based on orthogonal design and multi-objective effect optimization for rock mechanics parameters was set up by considering the advantage of orthogonal design and effect calculation on basis of theoretical analysis of displacement back-analysis method.3. According to the procedure of underground powerhouse excavation, each excavation was simulated using the method above, and the various excavation layer of rock mechanics parameters have been obtained.4. Using the rock mechanics parameters obtained by inversion, the stability of surrounding rock near the current excavation was analyzed and the variation law of displacement, stress and plastic zone were obtained. Then the calculations for the supportings of next excavation were done to forecast the distribution of displacement, stress and plastic zone base on the results.5. According to the forecast analysis results of each excavation, the guiding suggestions focused on reinforcement treatment of the weakness of dykes and faults that may impact on the stability of surrounding rock excavation have been proposed and fed back to the construction sector in time.