Urban　rail　transit　construction　will　inevitably　encounter　tunnel　working　conditions　with　extremely　complex　surrounding　environment　and　buried　deep　shield　tunnel,　and　the　stability　of　the　tunnel　surface　cannot　be　ignored.　A　series　of　passive　instability　geotechnical　model　tests　were　carried　out　on　the　tunnel　faces　at　different　burial　depths.　The　earth　pressure,　lateral　earth　pressure　coefficient　and　soil　arch　area　evolution　law　caused　by　passive　instability　of　the　tunnel　face　in　sandy　cobble　stratum　were　studied.　Once　the　preset　position　is　reached,　the　rotation　is　stopped　using　the　cutterhead　and　the　screw　excavator　and　the　shield　machine　continues　the　jack,　simulating　passive　instability　of　the　tunnel　face.　The　results　show　that　the　soil　pressure　in　the　horizontal　earth　pressure　is　significantly　more　affected　by　the　passive　instability　of　the　tunnel　face　than　the　vertical　direction.　The　soil　in　front　of　the　excavation　caused　by　the　ejection　of　the　shield　machine　is　squeezed　and　moved　forward,　resulting　in　a　decrease　in　horizontal　earth　pressure　perpendicular　to　the　direction　of　shield　tunnel　excavation.　The　results　of　the　passive　instability　region　obtained　by　numerical　simulation　are　larger　than　those　obtained　by　model　experiments,　because　the　numerical　simulation　method　fails　to　consider　the　compacting　effect　caused　by　the　extrusion　of　sandy　cobble　formations.　It　can　be　found　that　the　uplift　value　of　C/D　=　1.0　is　significantly　greater　than　that　of　C/D　=　1.5,　which　also　confirms　the　conclusion　that　the　instability　area　with　a　relatively　small　burial　depth　is　larger　and　develops　farther　to　the　front　of　excavation.　©　2023