The Plastic Yield Loci of a Shallow VLA in Clay

摘要

According to the theory of plasticity, plastic flow develops normal tornthe yield surface. During penetration a VLA (Vertically Loaded Anchor)rnmoves ahead when the soil around it yields. The plastic yield locus of arnparticular anchor expresses the combination of vertical (V), horizontalrn(H) and moment (M) loads that result in failure in clay. Apart fromrndetermining the ultimate holding capacity, the locus can also be used tornpredict the relative magnitudes of the resulting plastic horizontal andrnvertical displacements respectively during penetration. Since the failurernmechanisms are quite different for shallow and deep anchors, the yieldrnloci would be different for an anchor at different dragging stages. It isrnreasonable to predict the entire penetrating trajectory by therncorresponding loci. The general aim of the current paper was torninvestigate the failure behavior of a shallow square anchor and, morernspecifically, to deduce the shape and nature of the yield locus in H-V-Mrnspace for the anchor at early dragging stage. The finite element (FE)rnanalyses were utilized to calculate the load combinations that result inrnfailure of the anchor. Load-controlled analyses were adopted. In eachrnanalysis a gradually increased couple and a dragging force pointing in arncertain direction were applied. When the soil around the anchor yielded,rnthe anchor moved significantly and the couple as well as the draggingrnforce approached to their limiting values, resulting in failure of thernanchor. A series of such analyses had been conducted. The results arernpresented in the form of plastic failure locus in H-V-M space. The studyrnshows that in the combinations of loads that result in failure of thernanchor coupling is evident among horizontal, vertical and rotationalrnload components. The strongest interaction exists between vertical andrnmoment loads. The study also indicates that the ultimate holdingrncapacities given by the three dimensional model are much bigger thanrnthat given by the plane strain model.