Large　ground　deformation　such　as　faults,　landslides　and　liquefaction　may　pose　a　serious　threat　to　the　structural　safety　of　buried　pipelines.　This　paper　presents　a　series　of　three-dimensional　numerical　simulation　of　horizontal　lateral　pipe–soil　interaction　in　medium　dense　sand,　discusses　the　failure　mechanisms　of　sand　under　different　depth-diameter　ratios,　and　examines　the　influence　of　depth-diameter　ratio　on　the　ultimate　bearing　capacity　of　sand.　Moreover,　a　simplified　analytical　model　is　proposed　based　on　the　failure　mechanism　of　soil　around　the　pipe.　According　to　the　limit-state　equilibrium　theory,　the　analytical　solution　of　the　ultimate　bearing　capacity　under　horizontal　lateral　motion　of　the　pipe　is　derived.　The　results　show　that,　in　the　limit　state,　the　soil　around　the　shallowly　buried　pipeline　forms　a　rupture　surface　extending　to　the　ground　surface　with　a　failure　shape　approximately　to　a　logarithmic　spiral.　The　ultimate　bearing　capacity　of　sand　increases　with　the　burial　depth-diameter　ratio　of　the　pipe,　and　finally　reaches　a　constant　value　at　the　critical　depth-diameter　ratio.　With　the　increase　of　depth-diameter　ratio,　the　pipe　displacement　required　for　shear　failure　of　soil　also　gradually　increases.　The　difference　in　ultimate　bearing　capacity　calculated　by　Chinese　codes　and　foreign　codes　is　due　to　the　different　empirical　lateral　bearing　capacity　coefficient.　The　analytical　solution　proposed　in　this　paper　can　favorably　predict　the　ultimate　bearing　capacity　of　soil　under　lateral　horizontal　movement　of　shallowly　buried　pipes　in　medium　dense　sand.　©　2022　Academia　Sinica.　All　rights　reserved.