Collapse　is　a　typical　type　of　accident　during　subway　tunnel　construction.　Complex　geological　conditions,　particularly　soil-sand-rock　composite　strata,　significantly　contribute　to　strata　instability,　posing　a　serious　threat　to　tunnel　safety.　Indeed,　the　progressive　failure　leading　to　the　collapse　of　subway　tunnels　in　these　composite　strata　exhibits　distinct　characteristics　from　that　of　single　strata　and　warrants　further　research.　In　this　paper,　model　tests　were　conducted　to　investigate　the　collapse　process　of　the　soil-sand-rock　composite　strata　under　different　overlayer　rock　thicknesses.　Soil　pressure　sensors　monitored　the　mechanical　response　of　the　strata,　while　a　two-dimensional　full-field　deformation　measurement　and　analysis　system　(XTDIC-2D)　provided　displacement　and　strain　fields.　Additionally,　an　industrial　camera　captured　video　footage　of　the　failure　process.　The　results　demonstrated　that　the　collapse　characteristics　of　the　soil-sand-rock　composite　strata　were　significantly　impacted　by　overlayer　rock　layer　thickness.　As　the　thickness　of　the　rock　layer　decreased,　the　collapse　easily　expanded　to　the　sand　layer　under　a　slight　loading.　The　sand　layer　exhibited　distinct　behaviors　with　high　compressibility,　thixotropy,　and　flowability　during　the　collapse　process.　The　high　compressibility　of　the　sand　layer　before　collapse　resulted　in　strain　concentration　within　it,　thereby　resisting　the　deformation　of　the　rock　strata.　After　the　collapse　of　the　rock　strata,　the　thixotropic　and　flowability　properties　caused　the　collapse　surface　to　expand　in　a　funnel　shape　towards　both　sides.　A　stabilized　stratigraphic　arch　could　not　be　formed　due　to　the　arch　foot　being　located　above　the　sand　layer,　which　cannot　provide　stable　support.　Overall,　the　results　of　this　research　offer　valuable　guidance　for　the　prevention　and　control　of　tunnel　collapse　in　soil-sand-rock　composite　strata.　©　2024　Elsevier　Ltd