Soft rock refers to the strength and elastic modulus of the bedrock is particularly low, some lithology is still hard, but due to the influence of weathering or fissure joint dense and become weak rock, and some due to the lithology itself weak. Usually, when choosing a dam site, we should try to choose a place with a hard rock, but with the development of good dam sites, sometimes we have to build in a place where the foundation is unfavourable.