Paramita Bhattacharya

Uplift Capacity of Anchors in Layered Sand Using Finite-Element Limit Analysis: Formulation and Results

AbstractThe vertical pullout capacity of strip and circular plate anchors embedded horizontally in a layered sandy medium was computed by using the plane strain and axisymmetric lower-bound limit analyses in combination with finite elements and linear optimization. The soil medium below the anchor plate was assumed to be comprised of loose sand. Two different sand layers were considered above the anchor with different combinations of their internal friction angles. For several embedment ratios (H/B), the variations of the pullout factors Fγ and Fq due to the components of soil unit weight and surcharge, respectively, were computed as a function of Hdense/H for different cases; here, H and Hdense imply (1) the depth of the anchor plate from ground surface and (2) the thickness of the dense sand layer, respectively. The pullout resistance increased continuously with an increase in Hdense/H. For a given H/B, with the same value of Hdense/H, the uplift resistance became greater for a case when the dense sand ...

Seismic pullout capacity of vertical anchors in sand

The horizontal pullout capacity of vertical anchors embedded in sand in the presence of pseudo static horizontal earthquake body forces has been determined by using the lower bound finite element limit analysis. The variation of the pullout factor Fγ with changes in embedment ratio of the anchor plate for different values of horizontal earthquake acceleration coefficient (αh) has been established. The effect of the anchor-soil interface friction angle on the results has also been examined. The pullout capacity decreases quite significantly with an increase in αh. The pullout capacity becomes higher for greater values of embedment ratio and interface friction angle. The normal pressure distribution along the front surface of the anchor plate and the development of failure patterns have also been examined.

Vertical pullout capacity of horizontal anchor plates in the presence of seismic and seepage forces

In the presence of pseudo-static horizontal earthquake body forces and horizontal seepage forces, the vertical pullout capacity of horizontal plate anchors buried in sand has been determined by using the lower bound theorem of the limit analysis in combination with finite elements and linear optimisation. The variations of the pullout factor (a) Fγ with, and (b) the factor Fq with αh, have been established for different embedment ratio of the anchor plate and the friction angle of sand. It is noted that the pullout capacity decreases continuously with increases in the values of αh and . The pullout capacity becomes continuously higher for greater values of the embedment ratio and interface friction angle. The failure patterns have been found to become unsymmetrical in the presence of horizontal body forces.

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.

Reducing the Computational Effort for Performing Linear Optimization in the Lower-Bound Finite Elements Limit Analysis

This study describes a technique for reducing the computational effort for performing linear optimization while solving any geotechnical stability problem with the use of the lower bound finite-element limit analysis. In the proposed method, a lower order polygon is initially used to model the Mohr-Coulomb yield function; the order of the polygon refers to its total number of sides. The initial solution is used to identify the governing side of the yield polygon that lies nearest to the point defining the existing stress state. Subsequently, this governing side of the linearized yield polygon is replaced with a number of the relevant sides of the higher order polygon. Because all the sides of the higher order polygon for imposing the linearized yield constraints do not enter the formulation, the associated computational effort becomes much smaller. With the proposed algorithm, the collapse loads were determined for smooth and rough strip footing, and the computational results were found to be quite convin...

Experimental Study on Uplift Capacity of Horizontal Circular and Strip Anchor Plates in Two-Layered Cohesionless Soil

Load-displacement behaviour and vertical uplift capacity of horizontal anchor plate embedded in layered sand deposits have been investigated by conducting laboratory model tests. Strip and circular plate anchors are used for this purpose. The layered sand deposits have been prepared with local sand having relative densities 25% (loose sand upper layer) and 65% (medium dense sand with bottom layer), respectively. The medium dense sand layer is always kept closer to the anchor plate and the loose sand layer is kept close to the top surface in the layered sand system. The experiments have been conducted for different embedment ratios with different relative thickness of the dense sand layer (Hdense/H). The maximum displacement of the anchor plate experienced at failure and the uplift capacity of the anchor plate have been found to increase with an increase in the thickness of the dense sand layer (Hdense) at any particular embedment depth (H). The present uplift capacity of the anchor plate determined experimentally is compared well with the available numerical solution.

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.

Closure to ``Uplift Capacity of Anchors in Layered Sand Using Finite-Element Limit Analysis: Formulation and Results'' by Paramita Bhattacharya and Jyant Kumar

The authors thank the discusser for pointing out a few typographic errors, which occurred because some of the figures used for the final production were slightly different from those used for correcting the proofs. Different versions of the files, unfortunately, created the difference at the time of final production. In Fig. 4, (1) the top-most solid and dashed lines are meant for H/B = 7, (2) the bottom-most solid and dashed lines correspond to H/B = 3, and (3) the intermediate lines are associated withH/B = 4– 6 from bottom to top. The legend of Fig. 1(d) remains exactly the same as that kept earlier for Fig. 1(c); (1) hollow circular markers are meant for a circular anchor plate, and (2) solid square markers are meant for a strip anchor. In Figs. 6(a–c), the top set of curves is meant for H/B = 6, and the bottom set of curves is associated with H/B = 4. For Figs. 6(a and b), there is no change in the definition of the axes; the vertical axis provides the values of Pu/(AgB). One can cross check it by comparing the results in 2(a) and 6(a and b). Note that, for H/B = 4 and 6, if the results of Fig. 2(a) are multiplied with H/B, then Figs. 6(a and b) will be obtained. For Figs. 6(a and b), Pu/(AgB) was determined with q = 0 but g = 0, and for Fig. 6(c), Fqwas obtained with q= 0 but g = 0. For the curves in Fig. 6(c), the hollow triangular marker is meant for the upper-bound results provided by Kumar (2003), and the remaining markers all correspond to the published lower-bound results by finite-element limit analysis. Fig. 5 shows the results forH/B = 5. The equilibrium equations that were followed for an axisymmetric problem are

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.