The Study Of Block Stability Of Ground Power System Excavations In Dadu River Ying Liangbao Hydropower Station

Proposed Ying Liangbao hydropower station locates in Lengqi town, Luding, Ganzi,Sichuan, which is the13th level of22levels hydropower station in Dadu River hydropowerplan. The normal pool level of reservoir is1246m. Total capacity is20.754millions cubicmeters. Regulate capacity is8.26millions cubic meters. The hydropower station has dailyperformance. Rocks in the area of the site of hydropower station is mainly diorite with a smallamount of granite. Surge-chamber in the area of the site is designed as high side wall forms,and underground powerhouse has a large span. According to investigation, the structuralsurfaces in2engineering positions develops so many that the blocks stability problem inside-wall and roof is difficult to deal with. So, this article researches surge-chamber andunderground powerhouse of Dadu River Ying Liangbao hydropower station. In theprospecting adit, I had a detailed investigation to structures at all levels.Based on the engineering geological conditions of the area and the area of the site, andthe characters of structures at all levels, I induced several dominant, laying foundations forJudging the potential instability of blocks. After that, according to measuring cranny andRQD, I preliminary divided the rockmass structure type, it provides a theoretical basis onjudging block stability.After making a series of achievements, I used equatorial projectionmethod to judge the formation of potentially unstable blocks in chambers, and found3different types of blocks, they include deterministic blocks, semi-deterministic blocks andrandom blocks. At last, I used SASW and Unwedge to calculate the blocks’ parameters, suchas shape, size, stability coefficients of sliding mode and so on, and made contrast on databeing calculated by two different softwares to ensure its accuracy. Through the above study, Igot the overall merit of blocks stability in engineering positions of area of the site. It providesreasonable basis for the design, construction and monitor of Ying Liangbao hydropowerstation, improves the safety of construction, reduces unnecessary project costs, and alsoprovides reasonable basis for other block stability study of related engineering.The main achievements in the study are as follows: (1)The geological conditions in area of the site of Ying Liangbao hydropower station iscomplex. Its formation lithology is Proterozoic jining-Chengjiang diorite. Rockmass has astrong tectonization and alteration because of its old age. In the rockmass,it develops manysecondary faults and shuttered zones due to influence and control of regional Detuo fracture.The hydrogeological conditions is simple in area of the site. Groundwater is mainly bedrockfissure water and loosely stacked layers of pore water in quaternary system, which is suppliedby atmospheric precipitation recharge. The stress of rockmass belongs mid stress area, thehighest stress could be reached to18Mpa, and the stress is mainly tectonic stress.(2)The engineering positions in area of the site of Ying Liangbao hydropower stationweren’t found regional level Ⅰ and Ⅱ fault structures. There are only level Ⅲ and Ⅳminor faults or compress-crushed zone and level Ⅴ structure. Fault structure plane inengineering positions is mainly level Ⅳ structure. Dominant orientation is NWW trendingwith high dip angle, most of them have rough and wet surface. The dominant orientation oflevel Ⅴ structure in surge-chamber is NEE trending with high dip angle. The dominantorientation of level Ⅴ structure in underground powerhouse is NE trending with steep dipangle.(3)I have divided the rockmass structure of surge-chamber and underground powerhouseby two ways which are numbers of cranny in hole and RQD. The results tell us that therockmass structure divided by the1st way is worse than the2nd way. The reason for this maybe that the granodiorite in the engineering positions exists some hidden cranny, it makes themeasured value by RQD bigger. Moreover, the existing of group cranny causes the abovephenomenon. By taking all factors into consideration, the rockmass structure insurge-chamber and underground powerhouse is mosaic structure.(4)I used field information and project layout of area of the site to project the level Ⅲand Ⅳ structure exactly into the diagram. When I analyzed possible blocks on the side-wall,headwall and roof, I needed to ensure their positions in surge-chamber and undergroundpowerhouse, which is depended on the location and extension of structure surface and thePythagorean Theorem. After that, I could use equatorial projection method with crosssituation of fracture surface and occurrence of advantage cranny to judge whether it couldform deterministic blocks or semi-deterministic blocks or random blocks. The results gottenby equatorial projection method are as follows.1. The formed block types in the upper sidewall of surge-chamber are deterministic blocks, semi-deterministic blocks and random blocks.In the lower side wall and headwall, the types are only semi-deterministic blocks and random blocks. There are no level Ⅲ and Ⅳ structure in the roof,so the formed block type is justrandom blocks.2. The formed block types in the upper side wall, the lower side wall and roofof underground powerhouse are deterministic blocks, semi-deterministic blocks and randomblocks. In the headwall, the types are only semi-deterministic blocks and random blocks.(5)After preliminary judging the potential instable blocks, I used SASW and Unwedge tocalculate the stability and some other parameters of blocks. Although the results gotten by twodifferent software are not all the same, the scale of blocks formed in surge-chamber andunderground powerhouse are both small, and have a good stability. In sum, when we makeprecautionary measure of potentially unstable blocks during construction, we should deal withspot situation mainly based on the data calculated by SASW when the potential instableblocks presenting on the side-wall and headwall. If the potential instable blocks presenting onthe roof, we should deal with spot situation mainly based on the data calculated by Unwedge.In the surge-chamber and underground powerhouse, we should make blocks support byprestressed anchor, concrete anchor and reinforcement mat. When we use the roof bolt toanchor, to make sure the superior distance should be considered from the remaining slidepower of block, anchor diameter, rockmass strength and so on.