Baihe Jinsha River Hydropower Station Columnar Joints Basalts Rockmass Structural And Quality Classification

The Baihetan Hydropower Station located in the Jinsha River in Panzhihua to Yibin, the station in the lower reaches of the Jinsha River ,which is the second-class. The dam located on the Permian system top series Emeishan basalts layer. host strata occurrence flat overall, the dam area has't majorl fault, the geological conditions are better, the two sides of mountain are strong, hard, it is suitable for the construction of hyperbolic arch dam. But in view of the dam have a large number of columnar joint, it influences the rockmass structural and quality classification of the dam area, which is one major problem of the dam . So, the study of the spread rule and rockmass structural of columnar joints basalts ,research the means of quality classification has very important meaning. The results are as follows through detailed on-site investigation and comprehensive analysis.(1) Studied spread rule of columnar joints basalts in the dam area of Baihetan Hydropower Station.Get columnar joints basalts developed in the P₂β₂²,P₂β₂³,P₂β₃²,P₂β₃³,P₂β₄¹,P₂β₆¹,P₂β₇¹,P₂β₈² of the Permian system top series Emeishan basalts layers.the thickness of P₂β₃²,P₂β₃³ of columnar joints basalts is 34～59m,43～76m, they distributed on the riverbed and two sides low-elevation foundation,which has a very impointant maening for reference surface of high arch dam foundation. The figure of cylinder cross-section was the pentagon or the quadrangle which was irregular, surface of cylinder was ups and downs or distorted,rough and inlaid close.(2) Based on the study of the apparent feature, mineral feature and chemical feature of different degree of weathering of columnar joints basalts, taking into account of primary wave velocity,sound wave velocity and rebound number,divided the weathering belt into previous waek weathering,below waek weathering, Micro-weathering and Fresh rockmass. Weathering mainly along the tectonic structure, columnar joints, followed by micro-fractures in the Cylinder. The difference between weathering of columnar joints basalts and other basalts was that: they have different index with same weathering degree,the weathering index and rebound number of columnar joints basalts was bigger than other basalts when they in the same weathering degree.(3) Selected deformation parameter and shearing strength parameters of columnar joints basalts. We can conclude that the statistics histogram of modulus of deformation approximate normal distribution, horizontal direction is 6～18GPa, vertical direction is 4-12 GPa, horizontal direction obviously higher than vertical direction. It is proof that the rockmass anisotropy. Studied Physical and mechanical properties,deformation characters of columnar joints basalts and other basalts, horizontal modulus of deformation and vertical modulus of deformation ofâ…¡columnar joints basalts almost the same,but modulus of deformation ofâ…¢compare to other basalts was small, the difference is biggish ,rockmass easy to distot,shearing strength parameters of columnar joints basalts are lower. (4) Considering that the prismatic jointing basalt in Baihetan hydropower station dam region is a type of cataclastic and mosaic structure rockmass, and the apparent is also fragmenting, so when it's to specify the rockmass quality classification. The principal quantification designation of rockmass quality classification including three factors which are primary wave velocity, coefficient of integrity and ratio of rockmass permeability (Lu value). Suggested the method of rockmass quality classification which is suit for Baihetan Hydropower Station.(5) Applied the latest research achievement of rockmass of columnar joints basalts quality classification, suggested that the surface of high arch dam foundation should inâ…¢1,which is micro-new columnar joints basalts. Depending on the belt of weathering of dam basement rockmass, the rockmass quality classification and the permeability of rockmass, specified the position of reference surface of high arch dam foundation of Baihetan hydropower station.