Yuxia Hu

Three-dimensional large deformation finite-element analysis of plate anchors in uniform clay.

Three-dimensional large deformation finite-element (FE) analyses were performed to investigate plate anchor capacity during vertical pullout. The remeshing and interpolation technique with small strain approach was expanded from two-dimensional to three-dimensional conditions and coupled with the FE software, ABAQUS. A modified recovery of equilibrium in patches technique was developed to map stresses after each remeshing. Continuous pullout of rectangular plate anchors was simulated and the large deformation results for strip, circular, and rectangular anchors were compared with model test data, small strain FE results, and plastic limit solutions. Interface conditions of no breakaway (bonded) and immediate breakaway (no tension) were considered at the anchor base. The effects of anchor roughness, aspect ratio, soil properties, and soil overburden pressure were investigated. It was found that the anchor roughness had minimal effect on anchor performance. For square and circular deep anchors under immediate breakaway conditions, the maximum uplift capacity increased with soil elastic modulus, which suggests that lower bound limit analysis and small strain FE analysis may overestimate the capacity. The soil beneath the anchor base separates from the anchor at a certain embedment depth near the mudline, once tensile stresses were generated. The ratio of separation depth to anchor width was found to increase linearly with the ratio of soil undrained shear strength to the product of soil effective unit weight and anchor width and was independent of the initial anchor embedment depth.

Loss in anchor embedment during plate anchor keying in clay.

Vertically installed plate anchors have been investigated in this paper by numerical analysis and centrifuge modeling. In the numerical analysis, the large deformation finite-element method (remesh...

Keying of rectangular plate anchors in normally consolidated clays

The loss in anchor embedment during keying, as it rotates to become normal to the cable load, reduces the uplift capacity of anchors in normally consolidated clay. The keying behavior of plate anchors has been studied previously by using centrifuge and field model tests. In this paper, a large deformation finite-element approach incorporating frequent mesh regeneration and allowing for evolution of the anchor-chain profile, was developed to simulate the keying process of rectangular and strip plate anchors. A parametric study was undertaken to quantify the loss in anchor embedment during keying in terms of the anchor geometry, soil properties, loading eccentricity, and inclination. The embedment loss decreased dramatically with increasing loading eccentricity and decreasing chain angle at the mudline to the horizontal. The loss in anchor embedment during keying increased as the local soil strength increased relative to the weight of the anchor, up to a limit determined by the eccentricity of loading. In c...

Three-Dimensional Large Deformation FE Analysis of Square Footings in Two-Layered Clays

In strong over soft two-layered clays, there is a potential for the footing to experience a punch-through failure, where the footing penetrates a large distance at a short time after the initial peak resistance is reached. Three-dimensional 3D large deformation finite-element analyses using 3D RITSS method were conducted to simulate the penetration responses of square footings in strong over soft clays. The effects of surface soil heave and soil layer interface deformation during footing penetration were studied in weightless soils. Fitted equations were proposed to express the footing capacity response against the penetration depth. Based on the fitted equations, formulas to calculate footing peak bearing factor and the corresponding penetration depth were developed. The peak footing capacity factor and the corresponding penetration depth increases with the increasing of soil layer strength ratio, relative top soil layer thickness and soil weight factor, thus the potential of punch-through failure was reduced accordingly. It was also found that the soil weight effect can be a simple surcharge based on the formula developed in the weightless soil. Design charts for the peak footing capacity factor and the corresponding penetration depth were developed. DOI: 10.1061/ASCEGT.1943-5606.0000400 CE Database subject headings: Deformation; Load bearing capacity; Layered soils; Clays. Author keywords: Large deformation; Punch-through; Bearing capacity; Double-layered soils; Square footing.

Spudcan penetration in loose sand over uniform clay

Punch through failures of spudcan foundations of mobile jack-up rigs have been reported every year. The potential of punch through failure of spudcan foundations on loose sand over uniform clay soils was studied numerically in the present paper. Large deformation finite element analyses were carried out to simulate the load-penetration responses of a 14m diameter spudcan during continuous penetration into this sand over clay soil. The numerical results were compared with existing centrifuge data. The critical penetration depths were derived from the load-penetration responses. The soil flow mechanisms, the shape of sand plug and the distribution of plastic points were also reported.Copyright

Installation of Stiffened Caissons in Nonhomogeneous Clays

AbstractA significant difference between predicted and measured installation resistance of stiffened suction caissons was identified due to the existing uncertainty regarding the mobilized soil-flow mechanisms. This paper describes an extensive investigation of stiffened-caisson penetration in nonhomogeneous clays undertaken through large deformation finite-element (LDFE) analysis to provide insight into the soil behavior during installation of a caisson. The soil-flow mechanisms around and between stiffeners, and inside and outside of the caisson, and the corresponding penetration resistances were presented from a parametric study, exploring a range of dimensionless parameters related to stiffened-caisson geometry, caisson roughness, and soil strength nonhomogeneity. The LDFE results were compared with centrifuge test data in terms of the soil-flow mechanisms and penetration resistance profile, with good agreement obtained. Three interesting features in the mobilized soil-flow mechanisms inside the caiss...

Interpretation of Layer Boundaries and Shear Strengths for Stiff-Soft-Stiff Clays Using Cone Penetration Test: LDFE Analyses

AbstractThis paper reports on a new framework for interpreting cone penetrometer data in stiff-soft-stiff deposits, with the aim at identifying layer boundaries and interpreting accurately the undr...

Interpretation of Layer Boundaries and Shear Strengths for Soft-Stiff-Soft Clays Using CPT Data: LDFE Analyses

AbstractThis paper describes a new approach for interpreting cone penetrometer data in soft-stiff-soft clay deposits. The identification of layer boundaries and interpretation of shear strength profile were of particular interest. The proposed approach was based on an extensive parametric study using large deformation finite-element (LDFE) analyses, with a standard cone penetrometer penetrated continuously from the soil surface. The LDFE model has been validated against existing theoretical solutions and numerical results, with good agreement obtained. Regardless of strength ratio between two successive layers, the interface of soft-stiff layers can be identified at 0.8D (D is the cone diameter) below the kink in penetration resistance curve in the top soft layer. The interface of stiff-soft layers can be demarked at 1.3D above the kink in the penetration resistance profile in the bottom soft layer. The undrained shear strength of a soft clay layer can be interpreted using a single-layer approach and the ...

Scale Issues and Interpretation of Ball Penetration in Stratified Deposits in Centrifuge Testing

AbstractA full-flow ball penetrometer is now routinely used in centrifuge testing for characterizing single-layer clay, silt, sand, and stratified soil samples. The behavior of the standard ball penetrometer (including the shaft) used in the field, penetrating through single and two-layer uniform clays, has recently been investigated. However, the ball penetrometers used in centrifuge testing has either a similar or higher area ratio (of the shaft to the ball) and significantly greater equivalent prototype diameter compared with the standard one used in the field. The thickness of the soil layers, however, are scaled accurately mimicking strength profiles in the field, leading to lower relative thickness of the soil layers. Large deformation finite element (LDFE) analyses were, therefore, carried out for the centrifuge ball penetrometers to investigate its performance in characterization of single- and double-layer clays. The results were validated against plasticity solutions and other previously publish...

Large Deformation FE Analyses of Cone Penetration in Single Layer Non-Homogeneous and Three-Layer Soft-Stiff-Soft Clays

Continuous profiles from in-situ penetrometer tests are now identified as essential for site specific soil investigation as part of designing offshore structures in deep and ultradeep waters and in highly layered seabed conditions. This paper describes the results from large deformation FE (LDFE) analysis undertaken to provide insight into the behavior of cone penetrometer penetrating through single layer non-homogeneous clays and three-layer uniform soft-stiff-soft clays. For the smooth cone penetration in non-homogeneous clays, the soil strength non-homogeneity factor was shown to have insignificant effect on the cone bearing capacity factor. However, for the rough cone, the bearing capacity factor in non-homogeneous clay was about 10∼12% lower than that in uniform clay. Bearing capacity factors for smooth and rough cones were also similar for non-homogeneous clay. For cone penetration in stratified soft-stiff-soft clays, a minimum layer thickness of 20 diameters was required to mobilise the full resistance of the stiff layer. The corresponding soil flow mechanisms are also discussed linking directly to the profile of penetration resistance.© 2014 ASME