Study On Rock Fractures And Rock Blocks In Wudongde Dam Area

The Wudongde hydropower station is the most upstream ladder of fourworld-class hydropower stations—Wudongde, Baihetan, Xiluodu and Xiangjiaba,which are being constructed on the downstream of Jinshajiang River. The project willhas tremendous benefits such as electricity generation, flood control and sedimentdesilting. The dam is located in the Wudongde valley between Yunnan and Sichuanand the underground powerhouses are suited in the rock masses on the banks ofJinshajiang River. A curvature arch dam will be constructed and the layeredlimestones and marbles will serve as abutments. The rock fractures and blocks aremain factors endangering the whole project and hence being the focus.The dissertation studies the rock fractures and blocks in dam area in detail basedon the Wudongde hydropower station project. The main contents cover:(1) statisticalanalysis for the measured fractures and three-dimensional (3d) fracture networkmodeling by an inverse method;(2) evaluating the2d and3d fracture persistence byprojection method on the basis of fracture networks, and discussing the distributioncharacteristics and scale effect of fracture persistence;(3)computing the blockiness foreach rock mass and analyzing the assemblage characteristics of blocks;(4)expandingthe blockiness modulus into three dimensions，determining the3d block modulus foreach rock mass and its grade;(5) identification of the stochastic blocks inunderground powerhouses, quantification of their amount, sizes and stability, andproviding suggestion for the construction.The following conclusions can be drawn from the research:(1) two fracturegroups are developed in dam area, with west and northeast dip directions;the fracturetrace length is lognormally or exponentially distributed with average values ranging in1.0~4.0m; the average spacing is wide or very wide; the maximum3d frequency is0.251m-3.(2) the2d persistence value of flat-dipping fractures for each rock mass isless than10.0%, and that of medium and steep-dipping fractures are in8.0%~22.5%and0~11.6%,respectively; In three dimensions, the persistence values of horizontal andlateral slip surface are in the range of0.5~4.0%and1.9~23.4%, respectively; the3dpersistence of lateral slip surface is approximately normally distributed and exhibitsconsiderable scale effect and oriented-independent characteristics duo to the fracturefeatures.(3) the blockiness degree differs from each rock mass; the maximum andminimum values are74.5%and0.14%, respectively; the majority of blocks are less than1m3in volume.(4)the3d blockiness modulus for each rock mass is greater than4.0and therefore each rock mass is integral or sub-integral.(5) the stochastic blocksare largely suited in the vault of the right powerhouse and the sidewalls of the leftpowerhouse; the majority of blocks are stable but removable; the largest block is152.0m~3;the maximum embedded depth of blocks can be up to8.8m, so it issuggested that the anchor bolts supporting the surrounding blocks should be greaterthan8.8m in order to guarantee the stability of the powerhouses.