Strip Anchor Plate Research Articles

Centrifuge Model Tests and Numerical Analysis of Uplift Capacity of Strip Anchors in Geogrid-Reinforced Sand

Anchor-type foundations are one of the foundation types used in structures subject to tensile forces. These anchors are generally designed according to the weight of the soil on them depending on the depth they are buried at and the frictional resistance obtained from the failure surfaces during failure. One method of increasing the uplift capacity of the foundation without increasing the burial depth is the use of geogrid material. In this study, the uplift capacities of strip anchor plates at different embedment depths were investigated by considering the geogrid effect placed in different combinations. The aim of the study is to investigate whether a more economical solution can be obtained by using geogrid without increasing the embedment depth of the anchor plate. Experiments were carried out using centrifugal experimental setup, which gives values closer to the real results. The tests were performed on sand of two different densities for anchor burial depths H/B = 2 and H/B = 5. According to the results, the uplift capacity is significantly improved when geogrid is used. As the reinforcement configuration, the use of a single geogrid layer placed just above the anchor plate with an inclination angle of 45 degrees gave more effective results than using the geogrid horizontally and vertically. In the study, up to 98% increases in uplift capacity were obtained with reinforcement. In addition, the prototype model was analyzed with a numerical program based on the finite element method, and the results were compared with the experimental results. As a result of the comparison, it was observed that the experimental and numerical results were compatible with each other. Suggestions for practice are presented using the results obtained.

Multi-scale pullout behaviour of strip anchor plates embedded in marine hydrate bearing sediments

Anchor plates are widely used in offshore platform infrastructure due to their great pullout bearing capacity. With the increasing extraction activities of oil and gas resources in sub-marine environments, strip anchor plates are likely to be embedded inside existing hydrate bearing sediments, which will inevitably change its pullout behaviour and bring hidden safety risks to the infrastructure. This paper establishes both DEM models and FEM models of the interaction between a strip anchor plate and the marine hydrate bearing sediments. The mechanical responses of the strip anchor plate subjected to vertical pullout loads are investigated under the conditions of different hydrate saturations and embedded depths. The failure modes obtained by both numerical methods are analyzed and discussed from both the macro and micro perspectives. The results show that the presence of hydrate significantly improves the pullout bearing capacity of the strip anchor plate. In the DEM simulations, the hydrate bearing sediment presents a brittle failure and develops shear bands which extend from both side-edges of the anchor plate to the ground. In the FEM simulations, hydrate bearing sediments are controlled by the ductile failure mode. The angle between the shear band and the vertical direction in the hydrate bearing sediment is controlled by the friction angle of the sediment.

UNIFIED METHOD FOR CALCULATION OF VERTICAL PULLING CAPACITY OF HORIZONTAL STRIP ANCHOR PLATE IN SAND

Currently, the research on bearing mechanism and capacity calculation of horizontal anchor plate has the problem of artificially distinguishing shallow and deep bury conditions without consistent standard. In this article, a logarithmic spiral shape function was proposed to describe the continuous evolution of the sliding surface of the soil around the anchor plate, and the unified mechanical model of ultimate bearing capacity was established with no need to consider the bury condition. According to the relationship among the buried depth of anchor plate, the distance from the sliding surface intersection to the anchor plate and the distance from the tangent point of vertical line of the sliding surface to the anchor plate, the limit equilibrium analysis method was used in three different situations to deduce the unified theoretical solution of vertical pullout ultimate bearing capacity of horizontal strip anchor plate. The results show that, the new mechanical model can well reflect the continuous variation of the sliding surface with the buried depth ratio, and no need to artificially distinguish the bury condition. In the comparative calculation and analysis of five test cases in loose and dense sand, the unified theoretical solution ranks the second among nine methods, and has good adaptability.

Variation Analysis of Uplift Bearing Characteristics of Strip Anchor Plate in Nonhomogeneous Materials

Abstract Considering the nonlinearity and heterogeneity of geotechnical materials, the ultimate pullout capacity of a shallow horizontal strip anchor plate is determined based on the upper-bound li...

A limit analysis of the ultimate pullout capacity of a shallow horizontal strip anchor plate embedded in slope

Aiming at calculating the ultimate pullout capacity of a shallow horizontal strip anchor plate embedded in complicated topographical regions, e.g., mountainous areas, a kinematic admissible velocity field of the curved failure mechanism is constructed for the shallow horizontal strip anchor plate embedded in slope, based on the upper bound limit analysis theorem, the nonlinear Mohr-Coulomb failure criterion as well as the associated flow rules. The ultimate pullout force and failure mechanism are deduced using the variation minimum principle. Influences of the inclination angle and embedded depth on the ultimate pullout force are discussed in detail. The results show that the ultimate pullout force of the anchor plate decreases with the increasing inclination angle and the failure planes of the above ground are no longer symmetrical with an obvious shifting to the down side of the slope. Along with the increasing embedded depth, the ultimate pullout force of the anchor plate increases with a larger failure scope of the above ground. The inclination angle has a greater impact on the ultimate pullout force of the anchor plate with a smaller embedded depth. This effect should be taken into account for reasonably characterizing the ultimate bearing feature of a shallow horizontal strip anchor plate embedded in slope.

Variation analysis of ultimate pullout capacity of shallow horizontal strip anchor plate with 2-layer overlying soil based on nonlinear M-C failure criterion

Based on the nonlinear Mohr-Coulomb failure criterion and an associated flow rule, a kinematic admissible velocity field of failure mechanism of the 2-layer soil above a shallow horizontal strip anchor plate is constructed. The ultimate pull-out force and its corresponding failure mechanism through the upper bound limit analysis according to a variation principle are deduced. When the 2-layer overlying soil is degraded into single-layer soil, the model of ultimate pullout force could also be degraded into the model of single-layer soil. And the comparison between results of single-layer soil variation method and those calculated by rigid limit analysis method proves the correctness of our method. Based on that, the influence of changes of geotechnical parameters on ultimate pullout forces and failure mechanism of a shallow horizontal strip anchor with the 2-layer soil above are analyzed. The results show that the ultimate pull-out force and failure mechanism of a shallow horizontal strip anchor with the 2-layer soil above are affected by the nonlinear geotechnical parameters greatly. Thus, it is very important to obtain the accurate geotechnical parameters of 2-layer soil for the evaluation of the ultimate pullout capacity of the anchor plate.

Undrained Uplift Capacity of Strip Plate Anchor Nearby Clayey Slope

The effect of the nearby clayey sloping ground on the undrained uplift capacity of strip anchor plates embedded in fully saturated clay has been analyzed. The analysis has been carried out by using lower bound finite element limit analysis. The distance (s) between the slope crest and plate is varied from 0 to a finite distance until there is no change in uplift force is noted with an increase in crest distance. The uplift capacity of the plate of width B has been studied for different combinations of (i) embedment ratio (H/B) varying from 3 to 7, (ii) slope angle (β) ranging from 10° to 40° and (iii) the normalized crest distance (s/B). Also the anisotropy and nonhomogeneous behaviors of the clay have been considered in the present analysis. Uplift capacity of the anchor plate has been found to increase with increasing value of the normalized distance (s/B) between slope crest and the anchor plate. The optimum value of s/B beyond which there is no change in uplift capacity of anchor plate has been found to increase with (i) an increase in slope angle (β) and (ii) the embedment ratio (H/B) of the anchor plate. The uplift capacity is also influenced by the anisotropic behavior and nonhomogeneity of clay. The strong vertical anisotropy and the increase in cohesive strength with depth cause more resistance against uplifting in comparison to the pullout resistance in the isotropic and homogeneous clay even in presence of the nearby sloping ground.

Seismic Pullout Capacity of Inclined Anchor Plates in Sand

By using the lower bound finite elements limit analysis, the pullout capacity of an inclined strip anchor plate embedded in a cohesionless soil medium has been computed with an inclusion of pseudo-static horizontal earthquake body forces. The variation of the pullout capacity factor (Fγ) with changes in horizontal earthquake acceleration co-efficient (αh) has been computed by varying the inclination angle (β) of the anchor plate between 0° and 90°. The results clearly reveal that the pullout capacity factor (Fγ) decreases significantly with an increase in the value of αh. The reduction in the pullout resistance due to seismic forces (1) becomes much more extensive for a vertical anchor plate as compared to the horizontal anchor, (2) decreases generally with increases in the soil friction angle (ϕ) and (3) increases with an increase in friction angle between soil and anchor plate (δ). The developments of the failure zone around the anchor plate were also examined by varying αh and β. The results obtained from the analysis compare well with the solutions reported in literature.

Numerical study of a vertical pullout capacity of strip anchor plate on a frictional soil

This paper presents a numerical study of the ultimate pullout capacity of an isolated stripplate anchor, using the finite element method by Plaxis 2D software. The plate anchor is assumedrigid horizontally installed in a frictional soil and subjected to a centered vertical load. The soilbehavior is governed by an elastic‐perfectly plastic law, and Mohr‐Coulomb criterion was adopted.The ultimate pullout capacity is expressed in terms of pullout factor Nγ for different values of thedepth H and the internal friction angle of soil φ'. The numerical results obtained allow us topropose a simple relationship to calculate the pullout factor of a strip plate anchor embeddedhorizontally in frictional soil. The numerical results of this study are finally compared to thoseavailable in the literature.

Pullout capacity of strip plate anchor in cohesive sloping ground under undrained condition

The pullout capacity of strip anchor plates embedded in clayey sloping ground under undrained condition has been studied by using lower bound limit analysis with finite elements. The analysis has been performed for different values of (i) slope angle (β) varying from 0° to 40° with an interval of 5°, (ii) embedment ratio (H/B) of the anchor plate varying from 3 to 7 where H is the embedment depth and B is the width of anchor plate and (iii) c/γH ranging from 0.25 to 8 in addition to the case with γ=0. Three different orientations (θ) of the anchor plate, say horizontal (i.e. θ=0°), parallel to the ground surface (i.e. θ=β) and vertical (i.e. θ=90°), have been considered in the present study. For γ=0, the pullout capacity of both vertical and horizontal plate decreases with an increase in slope angle whereas the pullout capacity of anchor plate lying parallel to the sloping ground remains unchanged for all values of β. It has been observed that the pullout capacity of the anchor plate decreases with an increase in slope angle of the ground surface for γ≠0. The results are compared well with available results on pullout capacity of strip anchor plates with θ=0° and θ=90°.

Variation of Horizontal Pullout Capacity with Width of Vertical Anchor Plate

AbstractThe variation of pullout capacity of vertical strip anchor plates with width was studied while considering the effect of mean normal stress on the peak friction angle in a granular soil domain. This analysis was performed by using lower-bound finite-element limit analysis in conjunction with linear programing. The study was conducted for a wide range of anchor widths (B) and embedment depths (H) for both loose and dense sands. It was determined that the pullout capacity factor (Fγ = Pu/γBH) increases with decreasing values of normalized anchor width (γB/σA), where Pu is the ultimate pullout load; γ is the unit weight of soil mass; and σA is the atmospheric pressure. The rate of change for increments of Fγ with γB/σA was found to be more pronounced when the anchor is embedded in loose sand and at greater embedment depths.

Horizontal Pullout Capacity of a Group of Two Vertical Strip Anchors Plates Embedded in Sand

The horizontal pullout capacity of a group of two vertical strip anchor plates placed along the same vertical plane in sand, has been determined by using the lower bound finite element limit analysis. The effect of vertical spacing (S) between the anchor plates on the magnitude of the total group horizontal failure load (PuT) has been determined for different combinations of H/B, δ/ϕ and ϕ. The magnitude of PuT has been obtained in terms of a group efficiency factor, ηγ, with respect to the failure load for a single vertical plate with the same H/B. The magnitude of ηγ becomes maximum corresponding to a certain critical S/B, which has been found to lie between 0.5 and 0.8. The value of ηγ for a given S/B has been found to become larger for greater values of H/B, ϕ, and δ.

Effect of anchor width on pullout capacity of strip anchors in sand

By incorporating the variation of peak soil friction angle ([Formula: see text]) with mean principal stress (σm), the effect of anchor width (B) on vertical uplift resistance of a strip anchor plate has been examined. The anchor was embedded horizontally in a granular medium. The analysis was performed using lower bound finite element limit analysis and linear programming. An iterative procedure, proposed recently by the authors, was implemented to incorporate the variation of [Formula: see text] with σm. It is noted that for a given embedment ratio, with a decrease in anchor width (B), (i) the uplift factor (Fγ) increases continuously and (ii) the average ultimate uplift pressure (qu) decreases quite significantly. The scale effect becomes more pronounced at greater embedment ratios.

Vertical Uplift Capacity of Equally Spaced Multiple Strip Anchors in Sand

The ultimate uplift resistance of a group of multiple strip anchors placed in sand and subjected to equal magnitudes of vertical upward pullout loads has been determined by means of model experiments. Instead of using a number of anchor plates in the experiments, a single anchor plate was used by simulating the boundary conditions along the planes of symmetry on both the sides of the anchor plate. The effect of clear spacing (s) between the anchors, for different combinations of embedment ratio (λ) of anchors and friction angle (ϕ) of soil mass, was examined in detail. The results were presented in terms of a non-dimensional efficiency factor (ξγ), which was defined as the ratio of the failure load for an intervening strip anchor of a given width (B) to that of a single strip anchor plate having the same width. It was clearly noted that the magnitude of ξγ reduces quite extensively with a decrease in the spacing between the anchors. The magnitude of ξγ for a given s/B was found to vary only marginally with respect to changes in λ and ϕ. The experimental results presented in this study compare reasonably well with the theoretical and experimental data available in literature.