Since　the　ground　reaction　curve　(GRC)　is　a　useful　tool　for　evaluating　the　formation　deformation　and　the　load　acting　on　an　underground　structure,　it　is　critical　to　determine　the　GRC,　especially　under　small　strain　conditions.　In　this　paper,　a　new　analytical　model　considering　the　progressive　development　of　loose　soil　was　proposed　to　describe　GRC　in　trapdoor　tests.　The　proposed　model　is　composed　of　an　undisturbed　zone,　unloading　zone,　failure　zone,　and　self-weight　zone.　The　key　parameters　of　the　proposed　model　were　determined　through　the　existing　literature.　In　addition,　the　formulas　for　calculating　the　lateral　pressure　coefficient　and　the　height　of　the　failure　zone　were　derived,　respectively.　Considering　the　continuity　of　the　principal　stress　deflection　and　lateral　pressure　coefficient　in　the　unloading　zone,　and　assuming　that　the　unloading　zone　is　a　three-hinged　arch　with　reasonable　arch　axis,　the　load　transfer　expression　in　the　unloading　zone　was　deduced.　Then,　based　on　the　limit　equilibrium　theory,　the　vertical　stress　acting　on　the　trapdoor　was　obtained.　The　effectiveness　of　the　proposed　model　was　verified　by　comparing　the　calculation　results　of　the　proposed　model　with　model　tests,　a　theoretical　model,　and　a　simplified　model.　Finally,　the　influence　of　the　key　parameters　of　the　proposed　model　on　GRC　was　discussed　in　detail.　This　work　provides　a　meaningful　reference　for　estimating　the　GRC.　　©　2023　American　Society　of　Civil　Engineers.