Anchor Plates In Sand Research Articles

Method for calculating the uplift capacity of a circular anchor plate at arbitrary depth in sand

Methods for calculating the uplift capacity of horizontal anchor plates have the problem of artificially distinguishing shallow and deep buried types in advance, but the classification standards differ greatly. Based on the application of digital photographic measurement technology in experiment, this paper focuses on a theoretical method for calculating the uplift capacity of horizontal anchor plate in sand at arbitrary depth without distinguishing shallow and deep burial types. The results show that the sliding surface in the soil extends to ground surface in approximately a straight oblique line at shallow burial depths, then gradually confined within the soil as a balloon shape as the burial depth increases, and further shrinks toward the anchor plate. This change of sliding surface has no absolute boundary but undergoes continuous evolution, and can be described by a morphological function of logarithmic spiral line, which is used to develop a unified mechanical model, and a theoretical method for calculating uplift capacity is deduced and established. The new mechanical model well reflects the continuous variation of the sliding surface, and comparison with other four methods on 8 experimental cases show that the new calculation method has good adaptability for different types of burial depths.

Numerical and analytical investigation on inclined plate anchors in sand

The paper investigates the ultimate capacity of inclined plate anchors in sand through a series of finite element (FE) analyses. The FE simulations adopted a sophisticated bounding surface plasticity model that accounts for stress and density dependent behaviour, thus portraying a realistic estimate of the shear stresses and shear strains within the failure mechanism. The simulations considered a strip anchor with different plate widths, plate inclination angles and shallow embedment ratios in dense sand. The FE results show good agreement with previously reported experimental data. A limit equilibrium solution is subsequently proposed to predict capacity of inclined strip anchors in sand, based on mathematical expressions of the FE simulated normal and shear stresses along mobilised failure planes. The limit equilibrium solution is shown to produce satisfactory agreement with results from a large database of inclined plate anchors.

The performance of the dynamically installed plate anchor in sand and silt

Dynamically installed anchors (DIA) provide a time-efficient and cost-effective anchoring solution for offshore floating moorings. The dynamic installation and capacity mobilisation of the DIA in clayey seabed have been systematically investigated. However, the performance of the DIA in sand and silt is rarely studied. This study aims at investigating the performance of a newly proposed light-weight gravity installed plate anchor in sand and silt by conducting large deformation finite element (LDFE) analyses. Parametric studies were conducted to investigate the effects of varied factors on the final penetration depth of the anchor. By combining the present numerical results and previous experimental results, a comprehensive theoretical model was proposed for predicting the final penetration depth of the anchor in sand, silt and clay. Then the anchor-chain-soil interaction was simulated to investigate the keying behaviour of the anchor in silt, such that the motion trajectory and capacity mobilisation of the anchor could be derived. The conditions ensuring the anchor diving have been recommended.

Numerical investigation of pullout capacity for inclined strip plate anchors in sand

Plate anchors have been widely regarded as one of the most efficiency solutions for offshore structures in deep sea. Most of previous studies focus on the vertical or horizontal plate anchors embedded in sand. However, after the caisson foundation is withdrawn, the vertical plate anchor rotates to a certain angle from the horizontal plane in the process of resisting tension, which makes the analysis of pullout capacity of inclined plate anchors in sand relatively complex. This study, by using two dimensional finite element (2D-FE) method, takes a deep insight on the behaviour of strip plate anchors with different inclinations in loose to dense sand. A modified soil model is adopted to explore the hardening and softening behaviour of medium dense and dense sand. The FE results show a good agreement with previous numerical results and centrifuge test data. A series of FE cases are conducted to explore the effect of embedment ratios, plate inclinations and sand relative densities on the pullout capacity of inclined strip plate anchors. A new equation is proposed to estimate the ultimate pullout capacity of strip plate anchors with different inclinations in different relative densities of sand, which serves as a guidance for engineering design of inclined strip plate anchors in sand.

Closure to “Uplift Behavior of Pipes and Strip Plate Anchors in Sand” by Pei-Zhi Zhuang, Hong-Ya Yue, Xiu-Guang Song, He Yang, and Hai-Sui Yu

Closure to “Uplift Behavior of Pipes and Strip Plate Anchors in Sand” by Pei-Zhi Zhuang, Hong-Ya Yue, Xiu-Guang Song, He Yang, and Hai-Sui Yu

Discussion of “Uplift Behavior of Pipes and Strip Plate Anchors in Sand” by Pei-Zhi Zhuang, Hong-Ya Yue, Xiu-Guang Song, He Yang, and Hai-Sui Yu

Discussion of “Uplift Behavior of Pipes and Strip Plate Anchors in Sand” by Pei-Zhi Zhuang, Hong-Ya Yue, Xiu-Guang Song, He Yang, and Hai-Sui Yu

Uplift Behavior of Pipes and Strip Plate Anchors in Sand

AbstractThis paper presents an experimental study on the uplift behaviour of both pipes and strip plate anchors buried in sand. A total of 24 plane-strain uplift tests were performed using an image...

Inclined loading of horizontal plate anchors in sand

The performance of plate anchors in sand, relative to clay, is not well understood, particularly for the more realistic case of an inclined load. This paper investigates the effect of load inclination on horizontal plate anchors in sand through centrifuge tests and numerical finite-element simulations. The centrifuge tests were performed on rectangular plate anchors in loose and dense sand, at shallow embedment depths with four different load inclinations. The experiments showed that the anchor capacity of horizontal plates increased progressively as the load inclination became progressively more horizontal, with anchor capacity under pure horizontal loading being approximately 1·8 times higher than that under pure vertical loading. These experimental observations were also replicated in finite-element simulations using a bounding surface plasticity model. Investigation of the underlying failure mechanisms and stress paths showed that the slip planes become longer and the mobilised lateral stresses increase as the load inclination becomes increasingly horizontal, which leads to higher anchor capacities. Finally, the anchor resistance factors from the numerical analyses were decoupled into vertical and horizontal components and represented as interaction diagrams, providing a basis for performing hand calculations of anchor capacity for a given embedment depth, load inclination and relative density.

Ultimate pullout capacity of single vertical plate anchors in sand

This paper presents a limit equilibrium solution for calculating the ultimate pullout resistance of shallow vertical plate anchors in sand, considering the combined effects of anchor embedment ratio, sand shear strength, sand-anchor interface strength and anchor aspect ratio. The geometry of the failure mechanism in the solution reflects observations from model tests. The ultimate failure load of a strip plate anchor was then determined by global equilibrium analysis of the passive and active failure soil wedge. The two-dimensional limit equilibrium solution is extended for rectangular plate anchors by introducing the shape factors of Ovesen and Strømann. The solution is compared with a database of 102 pullout model tests of vertical plate anchors in sand assembled from the literature and some limit analysis results. The comparison results suggest that the proposed solution can provide a reliable analytical tool for the ultimate pullout capacity prediction of shallow vertical plate anchors buried in sand.

Pullout behaviour of inclined shallow plate anchors in sand

This paper presents an experimental study on the pullout behaviour of inclined shallow plate anchors subjected to axial pull in sand. The 1g model tests were performed to examine the effects of anchor inclination and sand–anchor interface conditions on the load–displacement response and the associated failure and deformation mechanisms of plate anchors at various embedment ratios and sand densities. The anchor pullout capacity was found to increase continuously with the load inclination angle to the vertical (α), and the increase was more significant for α from 45° to 90°. The effect of sand–anchor interface conditions was negligible for horizontal plate anchors (α = 0°), but it became increasingly significant at larger inclination angles. The effects of these two factors both decreased with an increasing embedment ratio. Their influences on the failure and deformation mechanisms were measured and analysed using a digital image correlation (DIC) technique. Based on the test data and results available in the literature, a simple empirical method for the prediction of pullout resistance of inclined plate anchors in sand is calibrated and recommended.

Numerical modeling of keying of vertically installed plate anchor in sand

Pile driven plate anchors are typically oriented vertically during installation. To function properly in a mooring system they must be rotated, or keyed, to an angle normal to the mooring line load. Keying involves reduction in anchor embedment, with concomitant reduced load capacity, so realistic prediction of embedment loss during keying is essential to design. This study investigates the kinematic behavior and load capacity of a vertically installed strip plate anchor embedded in uniform cohesionless soil using large deformation finite element (LDFE) analysis. Embedment loss during keying is evaluated as a function of load eccentricity, load angle, and plate thickness. The model indicates that the plate angle at which maximum pullout resistance occurs increases with increasing eccentricity. The finite element simulations also show the embedment loss during keying decreases with increasing load eccentricity. Loss of anchor embedment increases with increasing pullout angle. The model also predicts that the loss in anchor embedment increases with decreasing anchor thickness, especially when eccentricity is small. The simulations show anchor during keying was essentially independent of the soil elastic modulus to have virtually no effect on keying behavior for shallow anchors, but elastic effects can be significant for deeply embedded anchors.

Towards a simple and reliable method for calculating uplift capacity of plate anchors in sand

This paper investigates the uplift capacity of horizontal plate anchors in sand through finite element analyses and centrifuge experiments. The finite element simulations adopt a sophisticated bounding surface plasticity model that accounts for stress- and density-dependent behaviour, as well as loading- and fabric-related anisotropic effects in sands. Failure mechanisms at peak anchor capacity show that failure occurs progressively, with a marked decrease in mobilised friction angle within the shear bands close to the anchor edge. Numerical simulations of a large set of centrifuge experiments on rectangular, strip, and circular plates at different relative densities and stress levels are in good agreement for dense conditions, but perform more poorly for loose conditions due mainly to the open cone yield surface in the bounding surface model. Equivalent comparisons with current limit equilibrium methods highlight the challenges in direct application of element-level strength equations. Finally, the paper proposes a modified limit equilibrium solution based on a “rigid-block” failure mechanism extending to the soil surface, but with anchor factors that encompass the results from the finite element simulations. The modified solution provides a higher level of agreement with results from a large database of plate and pipeline test data than existing limit equilibrium methods.

Consolidation effects on monotonic and cyclic capacity of plate anchors in sand

This study investigated the change in monotonic and cyclic capacity of a plate anchor across different degrees of consolidation in dense sand. To quantify the effect of consolidation on anchor capacity, a framework is introduced and validated using centrifuge model anchor test data. The centrifuge tests considered a rectangular plate loaded at varying rates in dense sand, under both monotonic and irregular cyclic conditions, at a fixed embedment depth and with a horizontal load inclination (at the seabed). In order to vary from drained to undrained conditions, the sand was saturated using both water and a viscous pore fluid with viscosity approximately 700 times higher than water. The anchor's ultimate monotonic capacity in dense sand increased by up to 173% as the consolidation response evolved from drained to undrained with generation of dilation-induced suction. This increase in capacity across the consolidation regime can be adequately quantified using the proposed framework; however, uncertainty arises in achieving the theoretical undrained capacity. Both drained and undrained irregular cyclic loading resulted in anchor capacity increases of up to 33%, attributed to soil volume changes associated with cyclic densification under drained cyclic loading and excess pore pressure dissipation under undrained cyclic loading.

Correction: Evaluation of the efficiencies of helical anchor plates in sand by centrifuge model tests

<i>Correction:</i> Evaluation of the efficiencies of helical anchor plates in sand by centrifuge model tests

The effect of shape on the pull-out capacity of shallow plate anchors in sand

This paper presents an experimental and analytical study to investigate the effect of shape on the pull-out capacity of shallow horizontal plate anchors in sand under drained loading conditions. Novel dynamically penetrating plate anchor concepts have been proposed for use in the offshore energy sector. These anchor concepts may have shapes that are atypical, and the analysis of pull-out capacity of these shapes may be needed for design. Most of the research on the capacity of shallow horizontal anchors has focused on square, rectangular or circular shapes. Physical and analytical modelling was used to study the capacity of circular, square, triangular and kite-shaped plate anchors. The 1g physical model results indicated that the circular anchor had the highest capacity, which was up to two times higher than the square anchor, which had the lowest capacity of all shapes included in this study. The equilateral triangle and kite shapes had capacities that fell between the circle and the square shapes. A new generalised non-associated flow limit equilibrium model was developed to predict the pull-out capacity of shallow plate anchors with convex polygon anchor shapes. The model was most accurate at embedment ratios of 4 or less, with a bias of less than 10%.

Seismic uplift resistance of circular plate anchors in sand

In the present study, theoretical solutions have been developed for computing the vertical seismic uplift resistance of a shallow buried horizontal circular plate anchor in sand with the incorporation of shear transfer at the interface of the anchor plate and overlying sand during an earthquake. The analysis was performed by employing the kinematic theorem of limit analysis based on a pseudo-static approach, with the assumption of a simple rigid wedge collapse mechanism in the form of an inverted frustum with cross-section changing from circular at the anchor level to an elliptical shape at any level just above the anchor. The effect of seismic body forces on the uplift capacity of the circular anchor is evaluated in terms of dimensionless seismic factors Sq and Sγ due to the components of surcharge pressure and soil unit weight, respectively. An increase in the magnitude of seismic acceleration leads to a continuous reduction in uplift resistance; a significant decrease in the uplift resistance was found to occur for the case with the consideration of shear at the interface between the anchor top surface and the soil as compared to that without any shear.

Diameter effect on uplift capacity of horizontal circular anchor embedded in sand

ABSTRACT Variation of uplift capacity of horizontal circular anchor plate in sand with its diameter has been studied by using lower bound finite element limit analysis. The soil friction angle is a function of stress level. For plates with similar embedment ratios (H/D) but different diameter (D), the in-situ stress experienced at the top of the plate due to self-weight of the overlying soil would be different which resulting in varying degrees of the mobilized friction angle of soil. This would lead to varying capacity factors for plates of different diameters but similar H/D. The present numerical study has been conducted for wide range of D and H/D of rough anchor plates embedded in both loose Hostun and dense Toyoura sands. The uplift capacity factor has been found to increase with decreasing value of anchor diameter. The average uplift pressure, however, decreases with decreasing value of diameter of plate anchor.

Pull-out behaviour of vertical plate anchor in granular soil

In this paper, the pull-out behaviour of a vertical plate anchor in sand is investigated. Load-carrying capacity and failure displacement of the anchor are found to be significantly influenced by its embedment depth and the density of the fill soil. It is observed that a vertical anchor at shallow depth exhibits clear failure with the failure plane reaching out to the ground surface, whereas at deeper embedment the soil is subjected to constrained plastic deformation leading to localised failure around the anchor. The critical embedment depth beyond which anchor behaviour tends to shift from general to local shear mode is found to be 7h in the case of dense soil and 5h in the cases of medium dense and loose soils, where h is the height of the anchor plate. The proposed regression model is reasonably good in predicting the load-carrying capacity of the vertical anchors under pull-out.

Seismic uplift capacity of shallow strip anchors: A new pseudo-dynamic upper bound limit analysis

Using a new pseudo-dynamic approach for the inclusion of seismic body forces, the seismic vertical uplift capacity of horizontally placed strip plate anchors in sand at shallow depths has been computed with the application of upper bound theorem of limit analysis. Unlike the earlier pseudo-dynamic approaches, in this study, the nonlinear variation of both horizontal and vertical acceleration along the depth of soil layer, and in the values of amplitude and phase of accelerations has been considered with the satisfaction of stress boundary condition at the ground surface. The seismic uplift factor Fγs due to the unit weight of soil for different combinations of seismic acceleration coefficients, internal friction angle of soil, and the embedment ratio of anchors has been obtained. The solutions indicate that the magnitude of Fγs decreases substantially with an increase in seismic acceleration coefficients; whereas as expected, increases with an increase in embedment ratio of anchors and soil friction angle. This study produces the least upper bound solutions in comparison to the earlier reported results in the literature.

Geocell reinforcement for performance improvement of vertical plate anchors in sand

In this paper influence of geocell reinforcement on performance of vertical plate anchors is studied. A series of model tests were carried out in a test bed-cum-loading frame assembly. The anchor used was a steel plate of size 100 mm × 100 mm. With geocell reinforcement the anchor could sustain deformations as high as 60–70% of its height when the load carrying capacity was increased by four fold. The optimum length, width, and height of geocell mattress giving maximum performance improvement are found to be 5, 3 and 2.8 times the anchor height respectively. For adequate performance improvement size of geocell pocket opening should be close to the anchor size. The load dispersion angle that depicts the rigidity of the geocell mattress tends to increase with increase in its width, height and reduction in pocket size. A numerical study using fast Lagrangian analysis of continua was carried out. The agreement between observed and computed results is found to be reasonably good.