Excavation Sequence And Support Methods For Large And Complicated Underground Caverns

With the development of society and the improvement of technology, an increasing number of large engineering involves construction of underground cavern groups, especially for the hydropower engineering, which has got a rapid development recently. Limited by the complicated geological conditions such as high mountains and gorges, powerhouses are usually built in the underground in most of hydropower engineering. Due to the complicated structure interaction of the underground cavern, reasonable excavating sequence and support methods are of great importance to secure the stability and construction of the underground cavern group. Thus, the research of excavating sequence and support method would be urgent and promising for the construction and operation of the large underground engineering.In this research, underground cavern group of the powerhouse of the Ma’erdang Hydropower Station is studied. From the point of the dynamic evolution theory of the geo-stress field, based on the generalization of geotechnical conditions of the underground powerhouse area, comprehensive analysis the initial geo-stress field of the PowerStation zone. Three different excavation sequences and three different support methods were designed according to the pre-existing structure designing, the stress and failure characteristics of the surrounding rock under different excavating sequences were analyzed. Besides, simulation of the deformation, stress and distribution of the plastic region of the surrounding rock of the underground cavern group was studied with support. The main research contents are summarized as follows:(Ⅰ) Based on the analysis of the engineering geological conditions and the regional tectonic stress field around the dam, with the measured geo-tress data, the numerical simulate method were applied to analyze the characteristics of the initial geo-stress in the dam site zone. Use the facilities of numerical model of powerhouse area embedded in the dam area model; the initial geo-stress in the powerhouse area was simulated numerically deeply.(II) Three different excavating sequences were proposed on the basis of the research results of the initial geo-stress. in terms of stress redistribution of the surrounding rock, the optimum scheme was chosen by comparing the deformation and failure characteristics under three schemes, this can be used for selecting a reasonable setup of the future support structures.(III) The comprehensive analysis of the stress and failure features and the optimum scheme of excavating sequence would be a sound base of the selection of the support parameters of sprayed-concrete and bolt. The deformation, stress and distribution of the plastic region of the surrounding rock were simulated throughout the entire excavating and supporting process, then get the optimum supporting scheme, the reference would also been provided for the future congener engineering construction.