In model tests, the suction force beneath plate anchors is often eliminated by removing the soil beneath the anchor and providing an air vent to the space so created. The removal of soil, while ensuring complete removal of suction, can cause alteration in the soil failure pattern during pullout tests. To overcome this deficiency, a new method of eliminating suction has been evolved in which air vents are provided on the underside of the plate anchor. These are connected to the atmosphere through the pullout rod. This paper presents the results of pullout tests conducted on plate anchors in which suction was eliminated by the traditional method as well as the new method. It establishes that the new method eliminates suction as effectively as the traditional method while offering the advantage of not having to remove the soil beneath the plate anchor.
The vertical breakout capacity of a horizontal plate anchor embedded in soil is governed by the forces schematically depicted in Fig. 1. The thickness of the anchor " t" is usually so small, in comparison to the dimension B (Fig. 1), that Fv is negligible in comparison to the other terms. Plate anchors are not designed as dead weight anchors and, as such, Ws can also be ignored. In coarse grained soils, no suction force develops beneath the plate because of the high permeability of the soil. Consequently Psv is zero. However, in fine grained soils, significant suction force develops and its magnitude is comparable to Rv. This suction force cannot be used for withstanding long-term or sustained pullout loads. However, several anchor systems are being designed, for holding floating offshore structures in position, where this suction force is being used to withstand short term cyclic loads (Datta (1994)).