Note: This study is part of a broader project “Suction Caissons & Vertically Loaded Anchors: Design Analysis Methods” (MMS Project 362).
The study herein is concerned with predicting the undrained holding capacity of suction caissons under inclined load (combination of horizontal and vertical loads), such as applied by catenary and taut mooring systems. This study includes the effect of soil strength anisotropy on holding capacity. The primary prediction method proposed herein employs plastic limit analysis techniques, specifically the upper bound method to estimate the collapse load of a caisson. A three-dimensional collapse mechanism developed by Murff and Hamilton (1993) has been used for estimating the ultimate capacity of the laterally loaded caisson as well as the effect of soil anisotropy on caisson capacity. The loading rate is assumed sufficiently high that appreciable drainage does not occur (undrained condition) and simple, purely cohesive soil strength idealizations are employed. The soil undrained strength is assumed to vary linearly with depth. The effects of load application depth, caisson length to diameter ratio, soil strength characteristics, (surface strength and strength gradients) and soil unit weight effects are investigated.
Finite element analysis, FEM, a more rigorous and significantly more complex numerical procedure, is used to modify the plastic limit analysis for inclined loads as well as to verify collapse loads estimated with the plastic limit analysis. The constitutive models in the FEM include both isotropic and anisotropic (Hill’s criteria), elastic, perfectly plastic model using the von Mises generalization. The ABAQUS program is used in this research for all FEM analyses.
Related Publications: Aubeny, C.P., Han, S.W., and Murff, J.D. (2003) “Inclined load capacity of suction caisson anchors,” Intl. J. for Numerical and Analytical Methods in Geomechanics, Vol. 27, pp1235-1254.
Aubeny C.P. Han S.W.,and Murff, J.D. (2003) “Suction caisson capacity in anisotropic soil,” Intl. J. of Geomechanics, Vol. 3(4), pp225-235.
Aubeny, C.P., Han, S.W. and Murff, J.D. (2003) “Refined model for inclined load capacity of suction caissons,” 22nd International Conference on Offshore and Arctic Engineering, June 8-13, Cancun, Mexico, OMAE2003-37502.