Reseach On The Formation Mechanism And The Engineering Effects Of The Concentratioin Unloading Zone Of The YangQu Hydronpower Station On The Yellow River

The basement rock of the YangQu Hydropower station on The Yellow River was found many high-destiny tension cracks in it, and this phenomenon was a common thing in this canyon. It was have a certain width and tractility in the space of basement rock, so called it concentration unloading. The character which the unloading rock was in the certain horizon depth around is distinguishing form the normal unloading rock with surface unloading. There is large quantity of tension crack with clear width, and the rock has much cracks, and among the rocks was much space, so the rock mass was shatter to pieces and the rock mass quality was not good as the no-concentration-unloading zone.This article was based on the field investigation, and the interrelated date searching, such as the exploration data and the areal geology data of the YangQu Hydropower station on the Yellow River. And then the research which was based on those above on the concentration unloading zone mechanism of the YangQu lower reaches dam site and the interrelated engineering effect. Study maily on these fllow points:(1) Based on analyze of the areal geology data and interrelated date searching, the article was analyze on the areal tectonic geology structure, historical geotectonic, history of the Yellow River, etc.(2) This article was analyzed on the engineering conditions such as topography and physiognomy of Yehu Gorge, the formation lithology, the geological structure, the geohydrologic condition, the weathering and unloading characterizations, the karsts conditions and so on.(3) Based on the experimental tunnel investigation data and interrelated standard, the article was separate the different weathering and unloading zone with the qualitative and quantitative research. (4) Research on the concentration unloading zone development and distribution characterization, and the trend of the tension crack in the zone, the cracking condition, the tension crack cause type of formation, the mechanics of tension crack.(5) According the areal geology data, the engineering condition and the historical regional structure research, it shows that the concentration unloading zone formation factor was mainly a product of the special geological of this area. In the earlier period tectogenesis, the strain energy was to store up in the limestone. The strain energy was release in the cutting valley progress. The unloading effective was on the earlier high steep pitch fault or discontinues, it cause the creep-cracking on the gently dipping structure face, and form the concentration unloading zone at last. In other words, the concentration unloading zone of the dam site of the YangQu powerstation was a product of epigenetic Reformation of Rock Mass.(6) Using the FLAC3D, the article analyzed the stress and strain field of the nature condition, the excavation condition and the dam-load condition.Through the analyze of this article, the concentration unloading zone formation was mainly caused by the strong earthquake force, which is the initial factor of the tension crack by the shaking of the fault and fracture face, then the unloading and rebounding effective in the strong gorge vertical process.