Abstract With the development of grouting technique，it is widely used to treat soft soil. But in water conservancy and hydroelectric engineering，it is still very little to treat clay foundation with grouting. Through an engineering case，a series of detection methods，such as rock coring，high pressure water and loading test，and sonic test，ect.，are described in detail. At the end，it is pointed out that the river bed cover treated with grouting can¢t be used as composite foundation.
