| With the great development of West China, a new prosperous period of water power exploitation in the rugged mountainous area of Western China, where is rich in hydroelectric resources, is coming. It is usually needed to construct large scale underground projects for water power utilization in this area. Under these circumstances, the underground caverns with characteristics of large scale and complex spatial arrangement are located close in finite underground space. Thus the excavation effect and the interaction among different caverns during the process of underground projects construction are needed to be studied thoroughly which affect the cost of construction and production of power station.So taking the underground caverns of Laxiwa hydroelectric power station on Yellow River as an example, some problems closely related to the stability of rock mass surrounding underground caverns were analyzed in detail from the engineering geologic points of view. And the main contents of this dissertation are: (1)The engineering geological features of discontinuities in surrounding rock mass were analyzed on the basis of field geological survey and the preferred orientation of the main discontinuities were derived. Then the displaceable blocks distributing on the roof and sidewalls of main chamber were searched out taking the intersecting relationship of discontinuities into consideration. Then the failure mode and the coefficient of stability of the displaceable blocks were studied respectively. (2)The rock mass quality was assessed based on the data obtained from exploration adits with the methods of engineering geological classification for surrounding rock mass, BQ, RMR and Q-system successively. And then the correlations between the assessment results of different methods were discussed. (3)Based on the analyses results of simple inference method and seismic focal mechanism and on the statistic results of measured geostress data, the direction of principal stress was derived and based on the analyses results of macro geological estimate and on the statistic results of measured geostress data the magnitude of principal stress was derived too. The influence of rapidly down-cutting of Yellow River on geostress field of studied zone was discussed. Then the evolution of geostress field accompanying with the down cutting of Yellow River and was simulated with FEM and the spatial distribution features of geostress were discussed. (4)The influences of cavern shape, cavern scale and geostress on excavation effects for single cavern and the influences of distance between differentcaverns, rock mass quality and construction order etc on the excavation effects of caverns were studied. The features of multi-cavern effect of Laxiwa underground project were studied. (5) Selecting rock mass quality, excavation effect, multi-cavern effect and induced hazard effect as indexes, the stability classification scheme of rock mass surrounding large scale underground caverns was established. At last the stability of the surrounding rock mass of the main chamber of Laxiwa project was evaluated with this scheme.During the process of the fore mentioned analyses, some tentative works as follows were done.(1)On the basis of the fundamental of spatial analytic geometry, the basic method for displaceable block searching was put forward and the relevant program was written. With this program one can easily search out all the displaceable blocks and omitting of blocks, which is very common in searching blocks manually, can be avoided.(2)The coefficient of stability of blocks with failure mode II-2(that is, sliding on a single sliding surface, but confined by near intersecting line )was deduced.(3)The multi-cavern effect of Laxiwa underground caverns was studied on the assumption that all of the caverns were full face tunneled at the same time.(4)The stability classification scheme of rock mass surrounding large scale underground caverns was established. In addition to inherit the merits of the method of engineering geological...
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