Pullout Capacity Of Circular Plate Anchor In Saturated Clay

Plate anchors are commonly used as foundations for structures that require uplift resistance because of the characteristic of convenience and practicality. As the offshore oil/gas exploration moved to deep-water area, the anchors also are used in the floating platforms as a simple and economic anchoring system.One of the critical issues in the design of the anchor is to determine the uplift capacity of the anchor. In this thesis, the author takes a review on the study of the uplift capacity of anchors. Then the finite element analysis software-AFENA is employed to analyze the ultimate uplift capacity of anchors in saturated clay with two-and three-dimensional FE model. The constitutive model employed is Mohr-Coulomb plasticity with linear elasticity assumed within the yield strength surface. The effect of different strength ratio on the capacity and continuous pullout are considered in the two-dimension analysis, the effect of installation process on the capacity is also considered in two-dimensional analysis. The uplift capacity of anchors at different embedment depth and inclined degree are considered in three-dimensional analysis. The main conclusions are remarked as follows:1 For strong-over-soft two-layered clay, there is a relative critical distance H_cr—0.5D. When H>H_cr, the strength of upper layer has no effect on the capacity;For soft-over-strong two-layered clay, there also is a relative critical distance and it is decreasing with the increasing of strength ratio. Likewise, when H>H_cr, the strength of upper layer has no effect on the capacity.2 In continuous pullout analysis, the pullout capacity of the anchor shows four stages: stable in lower layer;passing the soil boundary;stable in top layer and soil-plat separation. In the first and third stages, the pullout capacity of anchor can be estimated by using single soil layer parameters. However, there is an increased pullout capacity comparing with the one for single soil layer. This increase is only significant at strength ratio less than 2/3. The initial embedment depth has little influence on the pullout capacity and soil-plate separation depth.3 For pre-embedded anchor in NC clay, the pullout capacity factors increase with the increasing of the uplift displacement for both attached and vented base. For vented case with k > 0.5kPa/m, the pullout capacity factors are lower than that for attached base. But when k = 0.5kPa/m, the pullout capacity factors for vented base are the same as that for attached base. The critical separation condition for uniform clay is still suitable to the normally consolidated clay.4 For installation process considered case, in the range of 5.5 < d/D < 6.0, the pullout capacity factors are much lower than that from pre-embedded case. That is because the installation process disturbed the soil.5 For inclined anchor, the pullout capacity factors increase with the increasing of the inclined angle at the same embedment depth. The inclined angle has no influence on the pullout capacity after the embedment depth reaches the critical embedment depth, 7 times diameter.