Uplift capacity of rapidly loaded strip anchors in uniform strength clay

The behaviour of horizontal strip anchors buried in clay is examined in this paper. A brief critique of the various approaches suggested for the design of these anchors is presented, with emphasis placed on estimation of the ultimate load that these anchors can withstand when loaded rapidly in uplift under undrained conditions. Possible mechanisms of failure are reviewed, including shear and tensile failure within the soil and the development of suction within the pore fluid, and the results of finite element predictions are compared with experimental data for ultimate loads. The analyses reveal that the behaviour of strip anchors in uplift is a function of the following non-dimensional parameters: H/B, gammaH/c and u(c)/c where H is the depth of embedment of the anchor, B is the width of the strip anchor, gamma is the unit weight of the soil, c is its undrained shear strength, and u(c) is the magnitude of the maximum tensile stress that can be sustained by the pore water in the soil. It is demonstrated that the ultimate uplift capacity is dependent on the availability of water at the surface of the soil and within the soil beneath the strip anchor. The analyses also show that shallow anchors in relatively strong soil tend to fail by the development of tensile failure in the soil above the anchor. The ultimate capacity of these shallow anchors is a function of the undrained shear strength of the soil, its self-weight and the tensile capacity of the pore fluid. By contrast, the failure mechanism for deeply buried anchors where the initial vertical total stress at the plate exceeds 7c involves only localised shear failure around the anchor, and as a result the ultimate capacity effectively becomes a function only of the undrained shear strength of the soil.