The great Wenchuan earthquake on May 12

2008 destroyed severely the earth dams in Sichuan Province and induced enormous economic losses.The damages of 44 earth dams of the high grade of risks in Youxian District

Mianyang City

Sichuan Province were analyzed and preliminarily summarized on the basis of scientific documents from the field investigation of seismic damages of reservoirs in Mianyang City

which have revealed that those earth dams destroyed in the earthquake were almost all built in the years of 1950-1980 and were designed without any aseismic considerations.The typical phenomena of the seismic damage of the dams include: the longitudinal cracks in the middle of the dam top and on the two sides of the dam axis

the longitudinal and transversal cracks in the dam body

and the local slips on the dam slope etc.It has been discovered

as well

that some sluiceworks were damaged

several wave-resisting walls were collapsed

a few upstream slope protection works were slid downwards

and a number of retaining walls on the dam slope were destroyed etc.All these facts indicate that the aseismic design is necessary for earth dams in the little reservoirs.Therefore

the damaging mechanism of earth dams should be studied thoroughly to guide the aseismic design for them.