This　paper　presents　a　new　3D　collapse　mechanism　to　investigate　the　face　stability　of　a　shallow　tunnel　embedded　in　the　saturated　and　multi-layered　soils　with　short-term　condition.　The　new　collapse　mechanism　is　composed　of　five　rigid　truncated　elliptical　cylinders　on　which　a　distributed　force　acts.　The　limit　support　pressure　is　determined　by　an　upper-bound　analysis.　A　simple　method　given　by　the　fitting　formula　is　presented　to　estimate　the　limit　support　pressure.　Analytical　solutions　obtained　by　the　new　collapse　mechanism　are　validated　by　numerical　simulations.　It　has　shown　that　the　proposed　collapse　mechanism　has　good　accuracy　and　efficiency.