The effect of discontinuities on the erodibility of rock in unlined spillways of dams

[摘要] Problems with erosion in unlined spillways of dams, have causedenvironmental and safety hazards, and necessitate the developmentof reliable scientific methods to assess the erodibility of thebedrock material.In an attempt to analyze the causes and effects of differentgeological, geotechnical, hydraulic, hydrological and engineeringdesign parameters on erosion of unlined spillways, a number ofdam spillways in the R.S.A. were studied. All the parametersconsidered important for the erosion resistance of the rock werecollected and correlated with hydraulic factors and observedextent of erosion.Rock type, strength, weathering and uniformity of the geologicalconditions are important geotechnical considerations whilevelocity and energy of the water flow are the main hydraulicparameters. The main consideration of the study was the effectof the discontinuities. All the properties of the jointing ofthe rock mass, such as number of joint sets, RQD, joint spacing,joint separation, joint orientation, roughness and fillingmaterial, were surveyed. Joints. weaken the rock mass and induceremoval of the rock blocks if the joint properties areunfavourable to stability. The jointed bedrock is much lessresistant to flowing or falling water, the result being anextensive and quickly formed scour.Various rock mass classification systems have been applied and a reasonable correlation between rock class and extent of erosionwas established by means of slightly modified Kirsten (1982) andWeaver (1975) rippability classifications.A number of methods for the prevention and repair of erosiondamage have been proposed.

[发布机构] University of Pretoria