Abstract: Left curb wall of the central discharging chute No.2 in Jinshuitan Dam is tightly close to the right wall of main powerhouse, powerhouse are inundated at central discharging because of defective concrete in chute, which seriously endanger the safety operation of the units. It was found that a wide range concrete casting defects were located in chute bottom by checks, so it is suggested that orifice closed backfill grouting on pressure only should be conducted.?