Uplift Behavior of Pipes and Strip Plate Anchors in Sand

Abstract

This paper presents an experimental study on the uplift behaviour of both pipes and strip plate anchors buried in sand. A total of 24 plane-strain uplift tests were performed using an image-based deformation measurement technique, by which the influences of anchor/pipe embedment ratio, sand relative density and pipe roughness on the load-displacement responses and associated failure and deformation mechanisms were systematically investigated. It was observed that the overall uplift responses of pipes and strip anchors were essentially similar. The peak uplift resistance of a strip anchor tended to be greater than that of a pipe at shallow depths, but the difference reduced as the sand-pipe interface frictional strength and the embedment ratio increased. Image analysis shows that the peak resistance of a shallow strip anchor/pipe was mobilised through the formation of an inverted trapezoidal block, bounded between a pair of inclined shear zones. The inclinations of the shear zones were dependent on sand dilatancy, and its average angle to the vertical for a strip anchor is slightly larger than that for a pipe. The shear zones initiate from the edges of an anchor invariably, whereas the initiation points may lie above the pipe waist, varying with sand-pipe interface conditions. These observations were used to modify a limit equilibrium method and a cavity expansion approach for predicting the peak uplift resistance of shallow pipes in sand. The modified methods were validated using a database of 125 shallow pipe uplift tests assembled from the literature. After the modifications, a good agreement with the overall database was shown, with average errors of less than 6%.