Study On The Jenesis And The Engineering Properties Of Interlayer And Interal Staggered Zones In Baihetan Hydroeletric Power Station Dam

Baihetan hydropower station is located in the lower reaches of the Jinsha River in Panzhihua and Yibin at the junction of Ningnan County in Sichuan Province and Qiaojia County in Yunnan Province. It is another planned ten millions of kilowatts project after Three Gorges and Xiluodu Water Conservancy Project in China. The interlayer staggered zones with greate thickness, good extensibility throughout the dam area, form the basic framework of the structures and rock structure; And the interal staggered zones with more general development in basalt layers, part of them with good extension, are important part of the rock structure. Through previous studies, the problem of construction features of the original basalt, development of columnar jointed basalt, characteristics of geological structure, development features of interal staggered zones, etc. has been basically solved. At present, the main problems are development of distribution space of the interal staggered zones, the degree of post-transformation of the staggered zones in different space site, and the different engineering properties with the different transformation process. Therefore, it is very important to study on the formation of the process and jenesis, and master the law and engineering properties of the staggered zones.In absorption based on the results of previous studies, divided the rock layer to determine the spatial location of the staggered zones. Make the qualitative description on material, scratch, properties of rupture. Sketch the fluctuation of them. And sample to measure the active ages. Screen to lay the foundation for analysing the late transformation process and engineering division characters. Summary the occurrence environmental geology background. The main line is tectonic-epigenetic-superficial reconstruction process. Combination with the tectonic and valley evolution history, discuss on the character and formation of the process, conceptual model of formation and evolution. At last, extract the staggered zones that may be the controlling bottom slip surface. Detailed analysis of the engineering properties to provide reference for parameter values and the evaluation of slope stability.This paper focuses on the occurrence environmental geology background of the staggered zones, the general characteristics of the construction and transformation, including the character of the construction of the original basalt, tectonic and epige-netic-superficial reconstruction process, the character of each staggered zone, including the spatial distribution and extensibility conditions, concluding the spatial development patterns and evolution of the three regions of tectonic, epigenetic and superficial reconstruction, and conceptual model of formation and evolution. Grading according to the slope stability level of risk with the staggered zones. Extracting the staggered zones that may be the controlling bottom slip surface. Finally, divide the engineering properties of the staggered zones according them in those three regions. Then make a brief evaluation and the treatment options.The main outcome of study as follows:(1)The developmental pattern of the interlayer staggered zones is main along-fissure type and density-fissure-belts type. The engineering property is main rockblock-debris type. And the dominant direction of interal staggered zones are N37°E,SE∠18°. The general width is thinner than 5cm. The interal staggered zones occurred in left bank are larger than them in right bank. There are more active groundwater around staggered zones which occurred diversity weathered belts in the range of 5~30cm.(2)The interlayer buildings by tuff are the basis of the formation of interlayer staggered zones. Horizontal micro-cracks developed in columnar jointed basalt at the bottom and lithologic contact zones, etc. are the the basis of the formation of the interal staggered zones.Six times tectonic stress fields of two regional tectonisms had experienced at dam area, while two of them were very important to the formation of staggered zones as directions of NWW-SEE and NNE-SSW. They lead to reverse and positive move-ment of staggered zones. Because of bend-sliding along the original tuff softness planes, the interlayer staggered zones formed. And most of the interal staggered zones are low angle ruptures associated, based on the rock flow level or the interlayer staggered zones of relative potentially shear planes, which abide the Riedal sheer mode.Two stages have been experienced during forming Jinsha River including gully and canyon period. Gully period corresponds to the regional erosion, and vertical unloading occurred to rock, separate-springback occurred along the staggered zones; while in canyon period, lateral unloading occurred, and diversity-springback occurred to the overhead plane. The epigenic reconstruction of the dam region mainly occurred in the slope rock mass stress adjustment, and positive movement occurred along the staggered zones, filling secondary sludge, forming the deep cracks to the bottom of them. The superficial reconstruction of the dam region mainly occurred continue to positive moving along the staggered zones as a result of gravity. Normal unloading fissures formed in a certain depth of the bank slope. The obvious evidence of the epigenetic-superficial reconstruction retained is nearbyⅠ~Ⅹprospecting line.(3) Based on the analysis results and features of each staggered zone, the bank slope is divided into three regions of tectonic, epigenetic and superficial reconstruction. They separately correspond to 220m in the left bank, 260m in the right bank; within 30~60m, and 180~220m out in the left bank, 220~260m out in the right bank; and 30~60m out. In the tectonic reconstruction region the thickness of the staggered zones are general less than 5cm, and the main project type is rock block-cutting, extending to this region they transform into sustained angle fracture filling with vain, or even thin out. Most of them have been re-cemented calcareous. The rock is quite integrity, and the groundword is inactive. In the epigenetic reconstruction region the thickness of the staggered zones increases. And the main project type is cutting-clip-mud or mud-clip-cutting, with mud bands and rock block-cutting interbedded. Most of the staggered zones are filled with secondary sludge. It forms the deep cracks under them. In the superficial reconstruction region characters further deteriorate. The thickness of the staggered zones and secondary sludge increased. The main project type is mud-clip-cutting. Secondary sludge, rock block and cutting mix together with poor cementation. With crushing rocks, cave is obvious. Unloading fissures are very common, and filling with lots of secondary sludge.(4)C2 is mainly affected by tectonic reconstruction and groundwater effect. And the evidence of epigenetic-superficial reconstruction is less remained. C3-1 is mainly affected by epigenetic-superficial reconstruction, less affected by tectonic reconstructtion than C2. There are many deep cracks and unloading fissures developping above them. C3 is less affected by tectonic reconstruction than both of them, integral moved not obviously. The interlayer staggered zones in right bank are mainly affected by tectonic reconstruction, also as most of the interal staggered zones. And the evidence of epigenetic-superficial reconstruction is less remained, too. The interal staggered zones with huge scale, long extension and great thickness usually experience the whole process including tectonic and epigenetic-superficial reconstructtion. The typical interal staggered zones include C3-1, C2, LS331, LS337, C-LS3310, and LS333, etc. which is important controlling bottom sliding face in dam region.