Study on the low velocity zone in surface layer of dam foundation and its engineering significations

摘要

There usually distributes a zone with lower acoustic wave velocity in surface layer of dam foundation after excavation. According to requirements which the dam foundation have to meet, the definition of low velocity zone is put forward. Then the relationships of the depth of low velocity zone with the lithology, the degree of weathering, the rock mass quality of dam foundation are analyzed in detail. A compositive map of low velocity zone in surface layer of dam is drawn up. And then the typical characteristics and the engineering significations of low velocity zone in the different parts of dam foundation are discussed detailed. Based on the analysis results the scope and depth of surface layer of dam foundation which need to be treated is suggested.