The　aim　of　this　study　is　to　investigate　the　coupling　effects　of　re-excavation　and　hydraulic　uplift　on　base　instability　of　pit-in-pit　(PIP)　braced　excavations.　The　numerical　model　of　PIP　braced　excavation　in　Shanghai　soft　clay　overlying　a　confined　aquifer　was　established　by　upper-bound　finite　element　limit　analysis　(UBFELA)　method.　The　effects　of　the　sensitive　design　parameters　(i.e.,　the　artesian　pressure,　thickness　and　undrained　shear　strength　of　the　aquitard　and　excavation　width　of　inner　pit)　on　failure　mechanisms　and　upper-bound　safety　factor　(FS)　against　hydraulic　uplift　were　analyzed.　The　results　show　that　the　value　of　FS　increases　with　an　increase　in　the　thickness　and　undrained　shear　strength　of　the　aquitard,　but　decreases　with　increasing　the　artesian　pressure　and　excavation　width　of　inner　pit.　The　failure　modes　can　be　typically　classified　into　three　categories:　circular　slip　surface　in　outer　pit　(M1),　hydraulic　uplift　combined　with　circular　slip　surface　in　entire　PIP　system　(M2),　and　basal　hydraulic　uplift　in　inner　pit　(M3);　then　the　corresponding　critical　artesian　pressure　is　determined.　Finally,　the　average　value　of　critical　artesian　pressure　used　to　distinguish　the　three　types　of　failure　modes　is　recommended　as　the　design　value　against　hydraulic　uplift　in　the　PIP　system,　and　validity　is　verified　by　the　comparison　with　the　current　design　methods.　The　proposed　stability　design　by　UBFELA　contributes　to　ensure　the　serviceability　and　performance　of　PIP　system.　©　2020,　Korean　Society　of　Civil　Engineers.