With oil exploration and production progressing into deep and ultra-deep waters, traditional jacket or gravity structures have been replaced by floating systems attached to the seafloor by vertical tethers or mooring lines. These floating systems require reliable and economical anchors. Among the most promising anchors at this time is the suction caisson, a cylindrical element pushed into the seafloor by self-weight and differential pressure induced by pumping water from the interior of the caisson. Depending on the application, a suction caisson can be subjected to vertical, horizontal, or inclined loads. Previous investigations have addressed the lateral load capacity issue, but the formulations were largely limited to isotropic soils. This research extends that work to account for anisotropic strength characteristics. For inclined loading conditions, this research develops load interaction relationships for a complete range of load inclinations between the horizontal and vertical limiting cases by using upper bound plastic limit analysis. The plastic limit analyses are supported by finite element studies in two ways. In the case of the inclined load investigations, the finite element analyses were used to develop the generalized stress interaction diagrams that form a key component of the plastic limit formulation. In all cases, the plastic limit formulations are validated through comparisons to finite element studies.
For estimating inclined load capacity, this research has produced a comprehensive set of predicted load interaction relationships for inclined loading conditions for a variety of soil strength profiles and caisson aspect ratios. A parametric study of lateral load capacity of a suction caisson using the anisotropic soil strength formulation developed in this dissertation has shown that an isotropic analysis using the simple shear strength of the soil can often provide reasonable agreement with the more rigorous anisotropic solution. Under certain conditions, such as the formation of a gap behind the caisson in conjunction with an unusually low triaxial extension strength, an isotropic analysis using the simple shear strength can be somewhat unconservative, but the over-estimate of capacity is less than 10 percent.
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