Research For The Surrounding Rock Mass Classification Of Soft Rock Mass In Danba Hydropower Station

Danba hydropower station is located in Sichuan Tibetan Autonomous Prefecturein Ganzi province Danba County in the Dadu River, eighth hydropower Dadu River22cascade development in the station, diversion type power. The outcropping ofbedrock in Danba hydropower station CPD1adit is in Silurian maoxian Group IVrocks group (Smx4). The plakite is almost among900m from the tunnel opening,which belongs to Smx4-2, a kind of soft surrounding rock. Reasonable evaluation ofthe soft surrounding rock mass quality to ensure construction safety of Danbahydroelectric power station cavern and engineering practice of normal operation is ofgreat value, but can also provide similar caverns in a hydropower project design andconstruction a theoretical basis.In more than two centuries, many scholars all over the world through a largenumber of exploration and practice, hundreds of surrounding rock classificationmethod is proposed. At present there are four commonly used rock mass classificationmethods, respectively, Q system, RMR method, the HC method and the BQ method;Comprehensive classification, they are all in the surrounding rock quality evaluation,considering the influence of various factors. But, the surrounding rock classificationmethod study of soft rock is much less, the applicability of the surrounding rockclassification of soft cave in danba hydropower station is not good enough, still needfurther research.Commonly used surrounding rockclassification is of good applicability inlow-stress, low water pressure, and under conditions of high stress, high externalwater pressure poor fitness, especially for mica schist of tunnel surrounding rockclassification of applicability is even worse.This paper takes CPD1adit stability and its deformation and failure situation as the foundation, studys on classification of rockmass quality of soft surrounding rock of cavern. Danba soft rock cavern rock stratumsuberect, belonging to a soft rock; tunnel strike and strike nearly perpendicular;cavern stability is good, after excavation, although without support can be long-termstability.The relative size of the normalized method is taken to compare differentsurrounding rock classification results.Based on field investigation and indoor test,using the Q system, RMR method, HC method, BQ method, and the S methodproposed by East China institute,this paper classifies the quality of surrounding rockofCPD1adit. Through comparative analysis with the actual rock types, results of expertevaluation based ondeformation characteristics and stability evaluation,this paperfinds advantages and disadvantages of various methods in surrounding rockclassification of soft rock tunnel.The applicability of the commonly used rock massclassification method in CPD1flat hole is poor, reasons mainly are:(1) consideringthe high geostress conditions is not enough: the RMR method without considering,the HC method is considering more general, Q system is not enough of considerationfor the extrusion of rock under high stress;(2) in view of the weak rock grading is notenough careful;(3) when the surrounding rock from hard rock into soft rock, somepart in the categories on the weights don’t make the appropriate adjustments.The structural plane in the flat hole CPD1islittle,and the quartz mica schistschistosity planeis much more. This article study from the theory angle, conclude thatthe plane is not strictly a planar structure, and is only characterized by planar failure,and the degree of planar failure of ups and downs has far exceeded the schistosity (thethickness of the micro flaky), the spacing and cut off before rock failure is classifiedas schistosity several similar surface below. From p-wave velocity measurement wayof the surrounding rock and the rock saturated uniaxial compressive strength testmethod etc. Research suggests that schistosity plane is part of the quartz mica schistitself, and not as structural plane in the surrounding rock classification. On this basis,and considering the quartz mica schist itself contains schistosity face this kind ofparticularity, based on the division of the rock mass structure type, quartz mica schistwill not contain discontinuities, denominate is "overall shape", contains the structureof the surrounding rock structure type named as "block like" etc, which differs fromno schistosity plane block rock mass.Parameters for the classification of surrounding rock are itemized necessarycorrection, respectively established for CPD1tunnel surrounding rock classification, SHC, SRMR and SQ.On this basis, the comprehensive soft rock tunnel surroundingrock classification system (SRCS system) was established for Danba soft rock tunnelsurrounding rock classification.Then this paper validates the rock classificationsystem from the aspects of relevance, consistency and applicability.SRCSclassification system in danba cavern buried deep application of weak surroundingrock classification results are in good applicability.To SHC, SQ andSRMRclassification, results with the actual rock types are more than80%. However,confined to the institute of surrounding rock classification system with data to CPD1flat hole hole diameter (about3m) is given priority to, when excavation cavity holediameter is larger, should according to the actual engineering conditions andclassification system (such as size effect and so on) for further improvement.Finally, with the study on the on-site support measures and numerical simulationanalysis, supporting measures on the soft surrounding rock of cavern in Danba areproposed.