Selection and verification of dam base surface for Zaoshi Hydroproject

The rock mass of dam foundation of Zaoshi Hydroproject is mainly fine silicarenite with soft layers.According to properties,the soft interbedded layer can be classed as soft rock layer,crushed stone layer,crushed stone muddy layer,argillization layer.The interbedded layers are poor in continuity with emergence of multiple thin-outs and cross stratification,local part liking lens and the properties vary comparably large for the influence of underground water distribution and intercalated sliding.Based on surveying data in preliminary design and concrete indexes of weathering state,structure type,rock integrity,rock strength,structural plane morphology and feature,permeability,engineering geological classification has been conducted for the dam foundation rock mass.Through statistical analysis and data quantification,the dam base surface is determined.The excavation construction verifies the dam base surface is correct in the preliminary design,and the analytical means and approach are effective and reasonable.