Effect of pore pressure dissipation on the behaviour of anchors in clay

Analysis of anchors subjected to a vertical uplift force has been carried out by using finite element analysis of a circular anchor embedded in a porous elasto-plastic material. The analysis takes into account the initial stress state, and makes allowance for breakaway if the effective stresses at the underside of the anchor fall to zero. A new axisymmetric joint element which can allow for the effects of fluid pressure has been used to examine the effects of breakaway. Two loading cases for the anchor are considered, rapid (or undrained) loading and slow (or completely drained) loading. Analyses are presented for "shallow" (2 diameters) and "deep" (4 diameters) anchors. The results show that the pore pressure reduction is not large enough to produce negative pore pressures behind the anchor.