Hydraulic　fill　sand　strata　in　coastal　areas　were　prone　to　differential　settlements　under　the　self-consolidation　to　form　undulating　ground　surfaces.Shallow　tunnel　faces　were　often　in　passive　failure　modes　when　shield　tunneling　in　hydraulic　fill　sand　strata.　However,　traditional　tunnel　face　stability　analysis　models　lacked　a　comprehensive　consideration　of　above　two　factors.　More　accurate　passive　failure　analysis　models　of　tunnel　face　under　undulating　ground　surfaces　urgent　need　to　be　explored.The　influence　exerted　by　longitudinal　slope　δ1　and　transverse　slope　δ2　on　the　ultimate　support　pressures　and　the　failure　zone　was　investigated　by　numerical　simulations.　According　to　the　failure　zone　obtained　from　numerical　simulations,　a　3D　passive　failure　model　was　proposed　by　using　the　spatial　discretization　technique,　and　ultimate　support　pressure　upper-bound　solutions　were　derived　based　on　limit　analysis　methods.　The　results　demonstrated　that　the　influence　of　bidirectional　slopes　cannot　be　ignored　in　practical　engineering,　the　longitudinal　slope　δ1　has　a　more　significant　impact　on　the　ultimate　support　pressure　than　the　transverse　slope　δ2,　the　effect　of　transverse　slope　δ2　on　the　extent　of　the　failure　zone　was　more　important　than　that　of　longitudinal　slope　δ1.Finally,　validated　by　comparison　with　numerical　models　and　existing　analytical　models　and　with　a　case　study.The　proposed　results　were　closer　to　numerical　results.The　results　can　provide　theoretical　guidance　for　shield　tunneling　under　complex　terrain　conditions.　©　2025　Editorial　Board　of　Journal　of　Basic　Science　and　Engineering.　All　rights　reserved.