| Xiaowan hydropower station, with its 292m high arc dam, is the largest one under construction in the Lancang river. The whole man-made rock slope reaches a maximum height of 600m. Because of its complicated rock masses structure and epigenetic recreation process accompanying with the river's cutting down, the stability of high rock slopes is very distinctive in this site. In this paper, one part of the high rock slope system called as IIIA-area is studied. A lot of evidenceds show that the stability of the high rock slopes in jointed rockmass is controlled by its structure ands failure model. Therefore, it has critical role to reveal the joints combinantion pattern and the mechanism of slope instability. Firstly, the basic rockmass strcture is investigated systematically in this slope. It reveals that the slope stability is mainly controlled by a set of joingts nearly parallel to the slope surface with a moderate to gentle dip angel. Obvisouly, its persistence ration is the most important factor among all the charatcteristics related to the stability analysis. On the other hand, the nature slopes and the excavated ones show a series superficial deformation and failure phenomena related to unloading process and time-dependent deformation, which are all described and recorded in detail in author's work. They tell us that the potential slipe surface exists on the boundary between intensively weathered rockmasses and weakly ones. So it can be concluded that the falire model of the IMA slopes is a sliping-tension one along the joints parallel to the slope surface at the depth of the bottom boundary of the intensively weathered zone of the slope.In order to obtain a precise description to the joint persistence ration, the author define two types of persistence ration according to different methods of measuring and statistics. One is the "belt persistence", which is defined as the total length of joints teace length in a 1m wide belt projected to a basic line (eliminating the overlay section) over the length of the basic line. Another is the one called as "search persistence" , which is defined a as the total length of joints trace length on the searched potential slipe surface over the length of the slip surface. Thus, the author establishes a measuring and calculation system to these definitions and finishes a great deal of field investigation aiming at the joints trace length and the "rock bridge" survey. Two methods give very similar results, 48.7% and 56.7% respectively. Comprehensively, author recommendes 60% persistence ratio to the slope stability anlysis.Finally, according to above research results, the author conducts the stability analysis of the MIA slope and puts forward the suggestion of slope support design. |
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