Summary
Note: Note this study is part of a broader project “Suction Caissons: Finite Element Modeling” (MMS Project 362).
The present work is an extension of the research reported by Vasquez (2000) and part of a comprehensive research project undertaken at the Offshore Technology Research Center (OTRC) at The University of Texas at Austin. The overall project aims at improving current understanding and developing effective procedures for the design of deep-water anchors (Olson et al., 2001). The research project focuses on several different topics: laboratory tests on model caissons subjected to axial pullout and inclined loads (El-Gharbawy, 1998;
Luke, 2002; and Coffman, 2003), development of a simplified prediction tool based on plastic limit analysis (Aubeny et al., 2003a), development of a highly detailed finite-element computational procedure (Vasquez, 2000; and Maniar et al., 2003), and reliability-based optimization of geotechnical investigations (Gambino and Gilbert, 1999; and Gilbert et al., 1999).
Vasquez (2000) presented the development of a finite-element procedure to simulate the response of suction caissons subjected to axial pullout under both drained (long-term) and undrained (short-term) conditions. The procedure was applied to study the laboratory tests reported by El-Gharbawy (1998). Simulation results obtained for caisson installation process as well as response of caisson under axial pullout were reported.
The objectives of the present research study are: (1) to develop a computational framework to simulate behavior of suction caissons and to estimate their capacities under axial as well as inclined loads, including effects of both self-weight and suction installation and (2) to simulate laboratory tests, conducted on model suction caissons at The University of Texas at Austin (Luke, 2002; and Coffman, 2003), in order to calibrate as well as validate the computational procedure.
The computational procedure developed in the course of this study simulates suction caisson installation and estimates the capacities under axial as well as inclined loads. Suction caisson installation and axial pullout are analyzed under the assumption of axial symmetry. The soil is modeled with water-saturated porous finite-elements and the caisson is discretized using (impermeable) solid finite-elements. The nonlinear behavior of the clayey soil is modeled through a bounding-surface plasticity model for isotropic cohesive soils, and linear elastic behavior of caisson is assumed. The soil-caisson interfaces are modeled with a contact algorithm based on a slide-line formulation. Various remeshing tools are developed to eliminate the need for a priori specification of the caisson penetration path and to avoid use of excessively
distorted finite elements along caisson-soil interfaces. The remeshing tool is an improvement over the procedure document by V´asquez (2000) in which the penetration path defined a priori as located immediately below the caisson tip and in the axial direction. This predefinition of the path did not account for
the soil movement during caisson installation process. Due to the restriction on the soil movement, the selected path over (under) estimated amount of soil within the caisson interior during self-weight (suction) installation. Due to this the computed capacity might have been affected as it is function of radial stresses generated within the soil domain during installation process.
The developed formulation is used to obtain results from the simulation of the caisson installation, and reconsolidation (or setup) of surrounding soil following caisson installation, and caisson pullout. Three-dimensional caisson models under horizontal and inclined loads are analyzed using the ABAQUS/Standard program. The deformed geometry of the caisson-soil system, stresses within the soil and material state parameters obtained from axisymmetric simulation of the installation process are specified as initial conditions to carry out analysis of caisson under horizontal and inclined loads. In addition, a user-defined material subroutine for the bounding-surface plasticity model is supplied to the ABAQUS program to model behavior of the saturated clayey soil. The computed behavior of the caisson is compared with the observed behavior in the laboratory tests conducted at The University of Texas at Austin (Luke, 2002; and Coffman, 2003).
Related Publications: Maniar, D.R. and Tassoulas, J.L., “Nonlinear Finite Element Simulation of Suction Caisson Behavior,” CD-ROM Proceedings of EM2002, the Fifteenth Engineering Mechanics Conference, New York, New York, June 2-5, 2002.
Rauch, A.F., Olson, R.E., Luke, A.M., Maniar, D.R., Tassoulas, J.L., and Mecham, E.C., “Soil Reconsolidation Following the Installation of Suction Caissons,” Proceedings, Offshore Technology Conference, OTC 2003, Houston, Texas, May 5-8, 2003
Maniar, D., Vásquez Chicata, L. F. G., and Tassoulas, J.L., “Installation and Pull-Out of Suction Caissons: Finite-Element Simulation,” Proceedings, OMAE ‘03, 22nd International Conference on Offshore Mechanics and Arctic Engineering, Cancun, Mexico, June 8-13, 2003.
Maniar, D. and Tassoulas, J.L., “Simulation of Suction Caisson Behavior During and After Installation in Normally Consolidated Soil,” CD-ROM Proceedings of EM2003, Sixteenth Engineering Mechanics Conference, American Society of Civil Engineers, Seattle, Washington, July 16 – 18, 2003.
Vásquez, L. F. G., Maniar, D. R., and Tassoulas, J. L., “Finite Element Analysis of Suction Piles in Saturated Clayey Soils,” Proceedings, SIAM Conference on Mathematical and Computational Issues in the Geosciences(GS03), Austin, Texas, March 17-20, 2003.
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