| As a clean and renewable resource, the foreground of hydropower is bright. In view of the hydropower resources of China are mainly concentrated in the mountain gorge area where the geological conditions are extremely complex, with characteristics such as large tectonic stress, strong unloading effect and high seismic intensity, and due to the limit of various factors, the vast majority of diversion power system of hydropower stations are in the form of underground structures. Building large underground caverns under the complex geological environments of high stress, strong unloading and high seismic intensity are facing enormous challenges, such as large relaxation depth of cave surrounding rock mass, high displacement quantity grade, collapse, rock blasting and the deep tension fracture of rock mass. It is difficult and costs more for the damage and crack arrest, deformation control and collapse treatment of large deep-buried cavern group. Recognizing the evolution of excavation disturbed (damaged) zone of underground caverns is essential to optimize the support parameters, construct safely and evaluate the stability and safety of project, and it has important practical significance and theoretical value. So the dynamic evolution mechanism of excavation damaged zone (EDZ) for underground caverns under complex geological environment, such as high geo-stress and super-large scale, need further research urgently.Setting the under construction caverns of Houziyan hydropower station as the research object in this research paper, and taking the theory of engineering geology, rock mechanics and damage mechanics as a guide, and combining a series of indoor rock mechanics testing and on-site monitoring of test data as well, it has studied the large number of deformation and failure phenomenon and the large depth of surrounding rock mass relaxation occured during excavation of caverns, discussed the dynamic evolution mechanism of excavation damaged zone in hard rock mass under high geo-stress. The following aspects are studied in this thesis:(1) Project Overview and geological environment. Research on the layout of underground caverns and geological environment background of Houziyan hydropower station, especially the characteristics of the geo-stress field, and it came to a conclusion that the characteristics of Houziyan region were higher practically observed values of ground stress, larger intermediate principal stress and lower strength-to-stress ratio.(2) The deformation and failure characteristics of metamorphic limestone under loading and unloading conditions. Based on the results of uniaxial compression with AE test, triaxial compression test, unloading test with high confining pressure and SEM fracture surface scan test of metamorphic limestone of Houziyan, it has systematically studied the whole process of deformation and failure of metamorphic limestone under different stress paths from AE events location, stress-strain curves, strength characteristics, macro - microscopic damage form and some other aspects respectively, and analyzed the deformation and failure mechanisms of metamorphic limestone under loading and unloading conditions. And the proportion relation between the stress characteristic values of metamorphic limestone was obtained by crack strain method.(3) The deformation and failure characteristics of surrounding rock mass of underground caverns in high geo-stress area. By analyzing the displacement monitoring data of underground caverns, the surrounding rock mass displacement magnitude, spatial distribution of deformation and deformation evolution was studied; And through on-site engineering geological survey, the surrounding rock mass failure phenomenon of underground caverns was categorized, and the spatial distribution characteristics and the time evolution characteristics of rock mass were studied; Then interpreted the deformation and failure characteristics of surrounding rock mass of underground caverns by using the stress mohr circle and the spatial distribution of stress field.(4) Research of the evolution mechanism of excavation damaged zone of surrounding rock mass of underground caverns in high geostress area. Based on the indoor rock mechanics test results and multi-point displacement meter monitoring results, the new standard - surrounding rock strain method was put forward to distinguish the EDZ of rock mass, and the new method was consistent with the common acoustic tests in a high level. According to the actual situation of Houziyan, the influencing factors, the temporal and spatial evolution characteristics and the failure mode of EDZ of underground caverns was studied by using the strain method. Combined the results of rock mechanics test and the Hoek-Brown criterion, a composite strength criterion was proposed, which could suit the ideal complete metamorphic limestone, and then used the composite strength criterion to study the geomechanical mechanism of the failure mode of EDZ of surrounding rock mass.(5) Research of mechanical parameters of EDZ of surrounding rock mass in high geo-stress area. Based on the analysis of the defects of the existing rock mass mechanics parameter estimation methods, the Hoek-Brown criterion of rock mass mechanics parameters estimation formula was improved by introducing the concept of rock mass integrity coefficient KVD under high geo-stress conditions. It applied the improved formula to estimate the rock mass mechanics parameters within the EDZ of main plant of Houziyan. And it focused on the vary regularity along the hole depth and the temporal and spatial dynamic evolution characteristics along with excavation of the rock mass mechanical parameters.The main innovations are as follows:(1) Obtained the proportion relation between the stress characteristic values of metamorphic limestone. Through rock mechanics test, the proportion relation among the closure stress, initiation stress, damage stress and peak stress of metamorphic limestone was obtained, which provided theoretical basis to predict the rock mass damage failure and damage control.(2) Proposed the rock mass strain method to distinguish the EDZ development regularity of the surrounding rock mass of large underground caverns. The rock mass strain method proposed in this research paper had the advantages of time continuity and had no restrictions of cavern parts, thus it could make up for the lack of acoustic test data.(3) Proposed a composite strength criterion, which could suit the ideal complete metamorphic limestone. And this criterion could reflect the failure mechanism under low pressure conditions better.(4) Proposed a new method to estimate the rock mass mechanics parameters in high geo-stress area. The Hoek-Brown criterion of rock mass mechanics parameters estimation formula was improved by introducing the concept of rock mass integrity coefficient KVD under high geo-stress conditions, and the improved formula could take the different degree of damage of rock mass under high geo-stress into consideration, thus to make sure the estimated results much more practicable. |
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