Face　passive　failure　can　severely　damage　existing　structures　and　underground　utilities　during　shallow　shield　tunneling,　especially　in　coastal　backfill　sand.　In　this　work,　a　series　of　laboratory　model　tests　were　developed　and　conducted　to　investigate　such　failure,　for　tunnels　located　at　burial　depth　ratios　for　which　C/D　=　0.5,　0.8,　1,　and　1.3.　Support　pressures,　the　evolution　of　failure　processes,　the　failure　modes,　and　the　distribution　of　velocity　fields　were　examined　through　model　tests　and　numerical　analyses.　The　support　pressure　in　the　tests　first　rose　rapidly　to　the　elastic　limit　and　then　gradually　increased　to　the　maximum　value　in　all　cases.　The　maximum　support　pressure　decreased　slightly　in　cases　where　C/D　=　0.8,　1,　and　1.3,　but　the　rebound　was　insignificant　where　C/D　=　0.5.　In　addition,　the　configuration　of　the　failure　mode　with　C/D　=　0.5　showed　a　wedge-shaped　arch,　which　was　determined　by　the　outcropping　shear　failure.　The　configuration　of　failure　modes　was　composed　of　an　arch　and　the　inverted　trapezoid　when　C/D　=　0.8,　1,　and　1.3,　in　which　the　mode　was　divided　into　lower　and　upper　failure　zones.　©　Higher　Education　Press　2024.