Suction　caissons　can　readily　penetrate　into　the　seabed　under　the　combination　of　the　self-weight　and　suction　resulted　from　the　encased　water　being　increasingly　pumped　out.　During　suction-assisted　penetration,　the　equivalent　overburden　at　the　skirt-tip　level　outside　the　caisson　is　generally　higher　than　that　inside　because　the　vertical　stress　within　the　soil　plug　is　reduced　by　the　exerted　suction.　This　may　result　in　a　uniform　shear　stress　developing　over　the　base　of　the　skirt-tip　as　the　soil　below　the　skirt-tip　tends　to　move　into　the　caisson,　which　leads　to　an　asymmetric　failure　wedge　existing　below　the　base　of　the　skirt-tip.　Besides,　different　adhesion　factors　along　the　inside　(alpha(1))　and　outside　(alpha(o))　of　the　skirt　wall　will　cause　asymmetric　plastic　zones　inside　and　outside　the　caisson.　Accordingly,　an　asymmetric　failure　mechanism　is　therefore　proposed　to　calculate　the　penetration　resistance　of　the　skirt-tip.　The　proposed　failure　mechanism　is　the　first　to　consider　the　effect　of　different　adhesion　factors　(alpha(i))　and　(alpha(o))　on　the　failure　mechanism　at　the　skirt-tip,　and　involves　the　contribution　from　the　weighted　average　of　equivalent　overburdens　inside　and　outside　caisson　at　the　skirt-tip　level.　The　required　suction　pressure　can　be　obtained　in　terms　of　force　equilibrium　of　the　caisson　in　a　vertical　direction.　Finally,　the　asymmetric　failure　mechanism　at　the　skirt-tip　is　validated　with　the　FE　calculations.　By　comparing　with　the　measured　data,　the　predictions　of　the　required　suction　pressure　are　found　to　be　in　good　agreement　with　the　experimental　results.