Study On The Ultimate Pull-out Capacity Of A New-type Vertically Loaded Anchor

The Vertically Loaded Anchor (VLA) is a new type of drag anchor that can work in deep waters, compared with other anchorage foundations applied in deep-water mooring systems, VLA has the advantages of convenient installation and recycle, recovery, higher bearing capacity. So it is widely accepted in deep-water projects.The ultimate pull-out capacity (UPC) is an important factor for weighing VLA performance. It is important to estimate the UPC accurately to provide for safety and normal work of the offsore structures, and meantime it is helpful for that plan the VLA's layout, optimize the VLA's arrangement, and thus reduce the number of VLAs, cut down the expenses and costs of installation and recycling.This thesis first gives an introduction to two models of Vertically Loaded Anchors and the methods of installation and recycle, and summarizes the current research status and research methods to the ultimate bearing capacity of VLAs at home and abroad. Then it introduces the three kinds of calculation methods for bearing capacity, analyses and compares the characteristics and relationships between Mohr-Coulomb and Drucker-Prager models and their differences in calculations, and also gives a description of contact problems and loading paths of displacement loads in numerical simulation. Finally, this thesis adoptes the numerical finite element method, according to a wedge-shaped VLA embedded in weightless saturated soft clay, adoptes Mohr-Coulomb elastic-plastic model in the FEM simulation ABAQUS software, by establishing the two-dimensional anchor-soil numerical model of coupled systems, to analyze the VLA stress stations and plastic flow mechanism of surrounding soil under working status.In the third chapter, through the simulation of wedged-shaped anchors embedded in soft clay, we obtain that the vertical anchor plates can withstand more pulling force than horizontal ones when buried shallow. Only when buried shallow the embedment angles have great influence on bearing capacity, and this influence became smaller along with the increase of embedment depth. Different buried depth the plates have different failure destruction forms, for shallow anchors the failure forms will be a whole damage of the soil above the anchor, the plates will be pulled out; while when embeded deep the failure forms will be a local shear failure of the soil around the anchor, the soil produces a local flow.In the forth chapter, according to the characteristics of soil is layered in nature, we assume that the soil is divided into two layers, both the upper and lower layers are well qualitative soil, the anchor plates are embedded into the lower-layer soil. By establishing anchor-soil numerical model of coupled systems, simulating and analysizing the different influences to the bearing capacity of different strength ratios(S_μ1/S_μ2) and different relative buried deepths (L/B), we obtain that for weak-strong two layer soil keep the relative buried deepths L/B unchanged, the bearing capacity of anchor plates increases along with strength ratios increases; with the same relative buried deepths, the bearing capacity is smaller as the soil strength smaller; the smaller of the relative buried deepth, the influence of the strength ratios to the bearing capacity would be more obvious. For the anchor plates embedded into strong-weak two layer soils, keep S_μ1/S_μ2 unchanged ,when L/B>1, the bearing capacity varies slightly, that is to say the upper soil has little effect on the bearing capacity; while L/B>1, the bearing capacity differ greatly, that is to say the upper soil has greater influences effect on the bearing capacity; in the case of keeping the relative buried deepth invariable, along with strength ratios S_μ1/S_μ2increases, that is to say with S_μ2decreases, the bearing capacity of anchor plates falls rapidly.