Jyant Kumar

Vertical uplift capacity of horizontal anchors using upper bound limit analysis and finite elements

The vertical uplift capacity of strip anchors embedded horizontally at shallow depths in sand is examined by using an upper bound limit analysis in conjunction with finite elements and linear programming. Velocity discontinuities were allowed along the interfaces of all the elements. The plastic strains within elements were incorporated by using an associated flow rule. The collapse load was expressed in terms of a nondimensional uplift factor

Effect of the Flow Rule on the Bearing Capacity of Strip Foundations on Sand by the Upper-Bound Limit Analysis and Slip Lines

F_\gamma

Upper bound solution for pullout capacity of vertical anchors in sand using finite elements and limit analysis

, which was found to increase continuously with an increase in both embedment ratio (\lambda) and the friction angle (\phi) of sand. Even though the analysis considers the development of plastic strain within all elements, however, at collapse, the soil mass just above the anchor was found to move as a single rigid block bounded by planar rupture surfaces making an angle \phi with the vertical. The results were found to be almost the same as reported in the literature for those based upon a simple rigid wedge mechanism.

Bearing Capacity of Strip Foundations in Reinforced Soils

AbstractThe influence of the flow rule on the bearing capacity of strip foundations placed on sand was investigated using a new kinematic approach of upper-bound limit analysis. The method of stress characteristics was first used to find the mechanism of the failure and to compute the stress field by using the Mohr-Coulomb yield criterion. Once the failure mechanism had been established, the kinematics of the plastic deformation was established, based on the requirements of the upper-bound limit theorem. Both associated and nonassociated plastic flows were considered, and the bearing capacity was obtained by equating the rate of external plastic work to the rate of the internal energy dissipation for both smooth and rough base foundations. The results obtained from the analysis were compared with those available from the literature.

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

The horizontal pullout capacity of vertical anchors embedded in sand has been determined by using an upper bound theorem of the limit analysis in combination with finite elements. The numerical results are presented in nondimensional form to determine the pullout resistance for various combinations of embedment ratio of the anchor (H/B), internal friction angle (ϕ) of sand, and the anchor-soil interface friction angle (δ). The pullout resistance increases with increases in the values of embedment ratio, friction angle of sand and anchor-soil interface friction angle. As compared to earlier reported solutions in literature, the present solution provides a better upper bound on the ultimate collapse load.

UPPER BOUND SOLUTION FOR PULLOUT CAPACITY OF ANCHORS ON SANDY SLOPES

AbstractA method is proposed to determine the ultimate bearing capacity of a strip footing placed over granular and cohesive-frictional soils that are reinforced with horizontal layers of reinforcements. The reinforcement sheet is assumed to resist axial tension but not bending moment. The analysis was performed by using the lower bound theorem of the limit analysis in combination with finite elements. A single layer and a group of two layers of reinforcements were considered. The efficiency factors ηγ and ηc that need to be multiplied with the respective bearing capacity factor Nγ and Nc to account for the inclusion of the reinforcements were established. The results were obtained for different values of the soil internal friction angle (ϕ). The critical positions of the reinforcements, which would result in a maximum increase in the bearing capacity, were established. The required tensile strength of the reinforcement to avoid its breakage during the loading of the foundation was also computed. The resu...

PASSIVE PRESSURE DETERMINATION BY METHOD OF SLICES

By incorporating the variation of peak soil friction angle (ϕ) 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 ϕ 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.

Upper-Bound Axisymmetric Limit Analysis Using the Mohr-Coulomb Yield Criterion, Finite Elements, and Linear Optimization

By making use of limit analysis, an upper bound solution in a closed form for determining the ultimate pullout capacity of plate anchors buried in sandy slopes has been established. The anchor plate orientation has been considered either horizontal or parallel to the slope, with the pullout force applied perpendicular to the plate. It has been found that the pullout capacity for horizontal anchors, even on slopes, remains the same as that on horizontal ground surface as long as the average embedment ratio is kept constant. Whereas for anchors which are aligned parallel to the slope the collapse load decreases continuously with the increase in the inclination of slope.

Bearing Capacity Factors for Ring Foundations

A method of slices satisfying all the conditions of statical equilibrium has been developed to deal with the problem of determination of passive earth pressure over a retaining wall in sand. A method similar to that of Morgenstern and Price 1 which was used to solve the stability of slopes, has been followed. The earth pressure coefficients with the proposed methodology have been computed for a vertical retaining wall for both positive and negative wall friction angle. Also examined is the variation of the interslice shear force between the retaining wall and the Rankine Passive boundary. Due to complete satisfaction of the equilibrium conditions, the method generates exactly the same earth pressure coefficients as computed by using Terzaghis overall limit equilibrium approach.

Stability of Unsupported Vertical Circular Excavations

AbstractAn upper-bound limit analysis formulation has been presented for solving an axisymmetric geomechanics stability problem using the Mohr-Coulomb failure criterion in conjunction with finite elements and linear programming. The method is based on the application of the von Karman hypothesis, and it requires only nodal velocities as the basic unknown variables. The computational effort needed to solve the axisymmetric problem becomes almost the same as that required for an equivalent plane strain case. By using the proposed method, bearing capacity factors were obtained for a circular footing placed over a cohesive-frictional soil medium. Nodal velocity patterns were also examined. Necessary comparisons have also been given to examine the usefulness of the proposed formulation.