Stiffened　deep　mixing(SDM)　columns,　as　an　innovative　composite　pile　technique,　are　widely　applied　in　the　soft　ground　improvement.　The　SDM　column-supported　embankment　may　suffer　instability　and　failure,　and　thus　understanding　the　failure　characteristics　of　the　pile　body　plays　a　critical　role　in　the　stability　calculation　of　embankments.　Considering　the　softening　characteristics　of　the　cemented-soil　and　the　plastic　damage　characteristics　of　the　concrete,　the　SDM　column-supported　embankment　stability　was　numerically　analyzed　through　two　pathways,　i.　e.,　overloading　on　the　pavement　and　reduction　of　subgrade　strength.　The　failure　mechanism　of　embankment　instability　was　explored,　the　development　law　of　the　plastic　zone　in　the　pile　body　and　the　mechanical　response　of　the　pile　under　overload　was　revealed,　and　the　bearing　characteristics　of　the　pile　body　during　strength　reduction　process　was　clarified,　determining　the　safety　factor　of　embankment　stability.　The　results　indicate　that　under　overload,　the　embankment　undergoes　typical　circular　sliding　failure,　dividing　the　pile　body　below　the　pavement　and　slope　into　the　compression　and　bending　zones.　The　outer　core　of　the　SDM　column　reinforces　the　inner　core,　and　compared　with　the　traditional　PC　pile-supported　embankment,　the　stability　safety　factor　of　the　SDM　column-supported　embankment　can　be　increased　by　13.7%,　with　the　maximum　horizontal　displacement　of　each　pile　in　the　SDM　column-supported　embankment　being　only　76%-82%　of　that　in　the　PC　pile-supported　embankment.　The　research　findings　can　provide　a　reference　for　the　design,　engineering　application,　and　promotion　of　the　SDM　column-supported　embankment.　©　2025,　Central　South　University.　All　rights　reserved.