Under　dynamic　cyclic　loads,　the　pore　water　pressure　in　saturated　sand　rises　continuously,　which　leads　to　the　reduction　of　horizontal　bearing　capacity　or　the　damage　of　the　pile　foundation.　Under　dynamic　cyclic　loads,　the　existing　calculations　methods　of　horizontal　bearing　capacity　of　pile　foundations　were　obtained　by　proposing　a　reduction　factor　for　the　static　p-y　curve　model　mostly.　Compared　with　the　test　results,　the　soil　resistance　around　the　pile　obtained　by　this　method　is　often　overvalued　and　the　pile-soil　relative　displacement　has　a　relative　underestimation.　As　a　result,　this　method　is　not　suitable　for　pile　foundation　design.　Therefore,　the　variations　of　soil　resistance　around　the　pile　and　the　pile-soil　relative　displacement　are　obtained　by　analyzing　the　effect　of　pore　pressure　ratio　on　soil　strength　around　the　pile　in　saturated　sand　in　this　paper.　The　theoretical　formulas　related　to　the　cyclic　vibration　times　and　pore　pressure　ratio　are　proposed.　The　proposed　formulas　are　introduced　into　the　dynamic　p-y　curve　model　to　obtain　the　dynamic　p-y　backbone　curve　in　the　process　of　sand　liquefaction.　The　research　results　show　that　the　variations　of　the　soil　resistance　around　the　pile　and　the　pile-soil　relative　displacement　are　related　to　the　pore　pressure　ratio　and　the　cyclic　vibration　times　during　the　sand　liquefaction.　As　the　cyclic　vibration　times　increases,　the　pore　pressure　increases,　the　soil　resistance　around　the　pile　decreases　and　the　pile-soil　relative　displacement　increases.　©　2023　Elsevier　Ltd