This study is concerned with predicting the holding capacity of suction caissons under horizontal loads, such as those applied through catenary mooring lines. The primary prediction method proposed herein uses a plastic limit analysis technique that has been originally developed to estimate the collapse load of a laterally loaded pile. The analysis is based on the upper-bound method of plasticity theory. A three-dimensional collapse mechanism developed by Murff and Hamilton (1993) has been used for estimating the ultimate capacity of laterally loaded cylinders under undrained conditions. In the analysis, the caisson is assumed to rotate about a horizontal axis through its center line due to a horizontal mooring load. The soil condition has been assumed to be approximately normally consolidated with a finite shear strength at the mud line, increasing linearly with depth. This condition is found frequently in many offshore basins including the deepwater Gulf of Mexico. The effects of load-point application depth, caisson length to diameter ratio, soil strength characteristics, and soil unit weight effects are investigated.
Finite element analysis, FEM, a more rigorous and significantly more complex numerical procedure, is used to verify collapse loads estimated with the plastic limit analysis. The constitutive model in the FEM is an isotropic, elastic, perfectly plastic model using the von Mises yield condition. The numerical analyses include both plane strain and three dimensional conditions.
Related Publications: Aubeny, C.P., Moon, S.K., and Murff, J.D. (2001) “Lateral undrained resistance of suction caisson anchors,” Intl. J. Offshore and Polar Engineering, Volume 11, No. 3, pp211-219.