The soft foundation earth-rock dam in the Chengmen lake in Chengmenshan copper mine of Jiangxi province was selected as a case study. Based on the characteristics of impact force during the silt flowing process

FLAC3D program was used to simulate and analyze the dynamic response of earth-rock dam

such as the horizontal velocity

displacement and shear strain

under the impact-squeezing action of silt. The research results are drawn as follows: (1) The variation law of the dam velocity is basically identical with the period of the impact-squeezing action. The monitoring point velocity and motion region in dam increase with the time. The monitoring point velocity reaches the maximum at about 0.3 s (1/2 period); while the motion region reaches the maximum at about 0.45 s (3/4 period). Afterwards

the dam tends to be static with the attenuation of the impact force. (2) Permanent displacement happens in the dam under the impact-squeezing action of silt. The average displacement is 30 mm

which can be seen that the whole dam moves 30 mm towards the downstream. (3) An obvious coalescence zone of shear strain increment generated in the dam is located in the upper soft foundation of the dam

which indicates that the dam will probably slide and damage along this coalescence zone.