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.　©　2017,　Science　Press.　All　right　reserved.