Jingbin Zheng

Spudcan Penetration Analysis for Case Histories in Clay

This paper reports advances in the prediction of spudcan resistance profiles during installation and preloading, based on the soil flow mechanisms observed in model tests and numerical analysis, and taking into account strain softening and rate dependency on the soil strength. Deep penetration of spudcan foundations was simulated for 14 case histories reported from different locations in the Gulf of Mexico, where the soils were single layer, predominantly normally to lightly overconsolidated clay. Axisymmetric and three-dimensional analyses were carried out using two large deformation finite-element (LDFE) approaches, modifying the simple elastic-perfectly plastic Tresca soil model to allow strain softening and strain-rate dependency of the shear strength. The field data were compared with the results of the finite-element analyses and with predictions using various design approaches. Excellent agreement was found, particularly when a mechanism-based design approach was used that differentiated between conditions before and after backflow of soil above the penetrating spudcan.

New Design Approach for Spudcan Penetration in Nonuniform Clay with an Interbedded Stiff Layer

AbstractThe paper describes a mechanism-based design approach for assessing spudcan penetration in soft nonuniform clay with an interbedded stiff layer. The proposed approach is developed on the basis of the results from a parametric study through large deformation finite-element analyses and validated against centrifuge test data. This can be taken as a “top-down” approach. Design formulas are proposed for assessing the limiting cavity depth and soil plug height. A direct comparison between the predicted profiles using the proposed design approach and the “bottom-up” approach recommended in an ISO standard confirms the benefit of using the former.

Numerical Modeling of Spudcan Deep Penetration in Three-Layer Clays

AbstractThis paper reports the results from numerical modeling of spudcan deep penetration through three-layer clays. Two typical seabed strength profiles commonly encountered in the field, and identified as critical for potential punch-through failure, were considered: (1) uniform stiff-soft-stiff clay and (2) nonuniform clay with an interbedded stiff clay layer. Three-dimensional large deformation finite-element (LDFE) analyses were carried out with and without simulating strain softening and strain rate dependency of the shear strength. The results were compared with previously published LDFE results and centrifuge test data. A detailed parametric study was undertaken, varying the relevant range of layer thicknesses (relative to the spudcan diameter), strength ratios, normalized strength, and strength nonhomogeneity. Punch-through and rapid leg penetration (for stiff-over-soft) and squeezing (for the reverse) were demonstrated by the penetration resistance profiles and associated soil failure mechanism...

Estimating spudcan penetration resistance in stiff-soft-stiffclay

AbstractThe paper presents a new mechanism-based two-step approach for assessing spudcan penetration resistance in three-layer stiff-soft-stiff clay sediments. An alternative approach is also propo...

3D large deformation FE analysis of spudcan foundations on layered clays using CEL approach

Spudcan foundations are used widely to provide support at the seabed for independent legged jack-up rigs. In order to explore the continuous load-penetration profile and mobilised soil failure patterns, simulating deep penetration of spudcans during preloading a jack-up rig, large deformation finite element (LDFE) analyses are essential. This paper investigates continuous penetration of circular spudcan foundations in single and two-layer clay deposits. An LDFE approach termed Coupled Eulerian-Lagrangian (CEL) approach in commercial package Abaqus was used. For implementing the CEL approach, a 3D model was created, in which only one fourth of the whole model was considered accounting for the geometric symmetry. Parametric LDFE analyses were performed encompassing the range of practical interest. The results from 3D CEL approach were compared with the previously published results from axisymmetric LDFE analyses using the RITSS (remeshing and interpolation technique with small strain) approach. The good agreement obtained shows that the CEL approach is capable in analysing complicated large deformation problems.