Preliminary Study Of The Unloading Zoning Feature On Dam Slope Area Of Songta Hydroelectric Power Station In Nu River Of Tibet

The water-power engineering of westen deeply incised valley areas wouldcome down to the unloading issue,research on the unloading and unloading zoning feature is of great theory and engineering significance in Rock-mass qualityclassification,foundation surface selection and rock-mass excavation.This paper take the bank slope of Nu River hydroelectric power station asthe object of study,based on the research at home and abroad, proceed the tunnel survey on site and indoor materials arrangement, analysed the factor of thecrack, the feature of the rock-mass structure, deformation and failure phenomenon, unloading failure mode and so on.Meanwhile use the numerical method tosimulate the process of the valley incision, and analysed the valley stress fielddistribution on the unloading condition. With the quantitative index obtained from the site material, I divided the bank slope rock mass into different unloading zones quantificationally, then compared it with zhe qualitative zoning result,At last, synthesizing the two date, determined the suggestive value. Specific research contents and results are an follows.(1) the rock mass structure characteristics and unloading fracture phenomenon researchThe features of the primary and tectonic structural surface is described through the investigation of the fracture with various causes in the tunnel, and then processed the conflation and statistic analysis, we got the structural plane distribution on space and the structure characteristics. Based on these, carrying on study on the surface structural planes. Combined with various unloading phenomena in the deeply incised valley, two types of unloading fracture in the dam slope area of Songta in summarized.(2) study of the bank slope unloading macro modeThe principal factors that influencing the development of bank slope unloading are summarized as the following: rock condition, structure of rock mass,channel and bank slope shape, valley evolution history and geostress level. Supplemented with numerical simulation method, we can intuitively analyse the stress field distribution and the plastic zone development characteristics, also prob e into the rock-mass unloading.rang. Meanwhile the author came up with the unloading characteristics of low angle dipping structural surface and the steep-gentle unloading composite pattern by analyzing the spatial unloading distribution.(3) Quantitative research of the rock-mass unloading zoningPicking up primary quantitative index from abundant geophysical date andtunnel survey index(fracture opening, fracture linear density, massiveness of rock-mass, longitudinal wave velocity and so on), using the picked indexes to divide the unloading zones, then compared the result with the qualitative unloading zone boundary, At last the final unloading zoning result which is suit for the dam slope area of Songta hydroelectric power station is given then.