Pile foundation is installed on the roof of karst cave under certain conditions. It is great significance to investigate the stability and the safety thickness of karst cave roof

when it is subjected to the coupling effect of the earthquake and pile-tip load. Based on the similarity theory and the separation similarity design method

dynamic failure characteristics of the cavern roof were studied by varying the roof thickness and cave diameter using the shaking table. Results show that the failure modes of the top of the cave roof are closely related to the thickness of the roof and the size of the cave in the earthquake. With a certain thickness of roof

when the cave-diameter was smaller than 2d (where d is the pile diameter)

shear failure happened in the roof. On the contrary

when the cave diameter was larger than 4d

punching-shear failure occurred. This indicates that the larger the diameter is

the greater the proportion of punching volume is. According to failure characteristics of the karst roof obtained by shaking table tests

the theoretical calculation model was proposed for minimum roof safety thickness

combining with the quasi-static method. Besides

the proposed model considered characteristics of rock mass

seismic intensity and pile diameter. It was shown by numerical studies that the minimum safety thickness was larger than that under static condition

and it increased with the increase of seismic intensity. Under the same condition

the calculated values of punching and shearing were larger than those of shear failure

which indicates that in the earthquake environment

the greater the cave size is

the higher the thickness of the required roof is. Therefore

this study can provide a valuable reference for developing the design approaches for the karst-pile in the earthquake region.