Jagdish Prasad Sahoo

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

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.

Stability of Unsupported Vertical Circular Excavations

A methodology has been presented for determining the stability of unsupported vertical cylindrical excavations by using an axisymmetric upper bound limit analysis approach in conjunction with finite elements and linear optimization. For the purpose of excavation design, stability numbers (S-n) have been generated for both (1) cohesive-frictional soils and (2) pure cohesive soils, with an additional provision accounting for linearly increasing cohesion with increasing depth by means of a nondimensional factor m. The variation of S-n with H/b has been established for different values of m and phi, where H and b refer to the height and radius of the cylindrical excavation. A number of useful observations have been gathered about the variation of the stability number and nodal velocity patterns as H/b, phi, and m change. The results of the analysis compare quite well with the different solutions reported in the literature

Vertical Uplift Resistance of Two Interfering Horizontal Anchors in Clay

AbstractThe vertical uplift resistance of two interfering rigid strip plate anchors embedded horizontally at the same level in clay has been examined. The lower and upper bound theorems of the limit analysis in combination with finite-elements and linear optimization have been employed to compute the failure load in a bound form. The analysis is meant for an undrained condition and it incorporates the increase of cohesion with depth. For different clear spacing (S) between the anchors, the magnitude of the efficiency factor (ηcγ) resulting from the combined components of soil cohesion (c) and soil unit weight (γ), has been computed for different values of embedment ratio (H/B), the rate of linear increase of cohesion with depth (m) and normalized unit weight (γH/c). The magnitude of ηcγ has been found to reduce continuously with a decrease in the spacing between the anchors, and the uplift resistance becomes minimum for S/B=0. It has been noted that the critical spacing between the anchors required to eli...

Vertical Uplift Resistance of a Group of Two Coaxial Anchors in Clay

The vertical uplift resistance for a group of two horizontal coaxial rigid strip anchors embedded in clay under undrained condition has been determined by using the upper bound theorem of limit analysis in combination with finite elements. An increase of undrained shear strength of soil mass with depth has been incorporated. The uplift factor F-c gamma has been computed. As compared to a single isolated anchor, a group of two anchors provides greater magnitude of the uplift resistance. For a given embedment ratio, the group of two anchors generates almost the maximum uplift resistance when the upper anchor is located midway between ground surface and the lower anchor. For a given embedment ratio, F-c gamma increases linearly with an increase in the normalized unit weight of soil mass up to a certain value before attaining a certain maximum magnitude; the maximum value of F-c gamma increases with an increase in embedment ratio. DOI: 10.1061/(ASCE)GT.19435606.0000599

Behavior of stabilized soil cushions under cyclic wetting and drying

Abstract The use of cushion below the base of foundation resting on expansive soil is very attractive from the view point of economy and overcoming the problems associated with construction of structures over expansive soil. Extensive studies on cohesive non-swelling soil (CNS) as a cushion show that it is not always effective with cycles of wetting and drying. With increase in the number of cycles, the CNS material has been shown to become less and less effective with time. Also, it is very rare to get CNS material in the nature. The present paper describes the possibility of using stabilized soil as a cushion material. The soil used as cushion in this investigation is not CNS, but its properties shows that it can be considered as a cohesive nonswelling soil. It has been observed that the soil cushion stabilized with lime and cement shows a substantial performance improvement in all the wetting and drying cycles and also in the key parameters i.e. highest swollen level, lowest shrunken level, equilibrium swollen and shrunken level, equilibrium band width, operating displacement, extreme displacement and operating middle level. Lime stabilized soil cushion is more effective than cement stabilized soil cushion.

Lower bound solutions for uplift capacity of strip anchors adjacent to sloping ground in clay

ABSTRACT Numerical solutions have been obtained for the vertical uplift capacity of strip plate anchors embedded adjacent to sloping ground in fully cohesive soil under undrained condition. The analysis was performed using finite element lower bound limit analysis with second-order conic optimization technique. The effect of anchor edge distance from the crest of slope, angle and height of slope, normalized overburden pressure due to soil self-weight, and embedded depth of anchor on the uplift capacity has been examined. A nondimensional uplift factor defined as Fcγ owing to the combined contribution of soil cohesion (cu), and soil unit weight (γ) is used for expressing the uplift capacity. For an anchor buried near to a sloping ground, the ultimate uplift capacity is dependent on either pullout failure of anchor or overall slope failure. The magnitude of Fcγ has been found to increase with an increase in the normalized overburden pressure up to a certain maximum value, beyond which either the behavior of anchor transfers from shallow to deep anchor or overall slope failure occurs.

Bearing Capacity of Shallow Strip Foundations in Sand under Eccentric and Oblique Loads

AbstractAn empirical nondimensional reduction factor is proposed in this paper, which can be used for determining the ultimate bearing capacity of eccentrically and/or obliquely loaded shallow strip foundations embedded in sand. This was developed after analyzing a series of laboratory model test results available in the literature on strip foundations. The depth of foundation (D), eccentricity of load (e), and inclination of load (α)varied from 0 to 1B, 0 to 0.5B, and 0 to 20°, respectively, where B refers to the width of foundation. The proposed reduction factor was found to provide reasonably well results for calculating the ultimate bearing capacity of shallow strip foundation under eccentric and/or inclined loads. The results obtained by using the proposed method have been found to be in good agreement with widely used traditional methods available in the literature.

Ultimate bearing capacity of shallow strip and circular foundations by using limit analysis, finite elements, and optimization

Abstract This paper presents a review of the works done mainly at Indian Institute of Science on the determination of the ultimate bearing capacity of shallow strip and circular foundations with the usages of lower and upper bound theorems of the limit analysis. After providing an outline of the historical developments in the field of limit analysis, a few important problems, illustrating the recent advancements in determining the bearing capacity of shallow foundations, have been addressed. The effects of (i) footing–soil interface roughness, (iii) size of footing, (iii) seismic forces, and (iv) interference of two closely spaced footings, on the bearing capacity have been presented.

Vertical uplift resistance of two horizontal strip anchors with common vertical axis

Abstract With an application of the upper bound finite element limit analysis, the vertical pullout capacity of a group of two horizontal strip plate anchors, with the common vertical axis and placed in a cohesive-frictional soil, has been computed. The variation of the uplift factors <i>F_c, F_q</i> and <i>F_y</i>, due to the contributions of soil cohesion, surcharge pressure and unit weight, respectively, has been evaluated for different combinations of <i>S/B</i> and <i>H/B.</i> As compared to single isolated anchor, the group of two anchors generates significantly greater magnitude of <i>F_c</i> for Φ ≤ 20° especially with greater values of <i>H/B</i> and under fully bonded anchor-soil interface condition. The factor <i>F_c</i> attains almost the maximum value when the upper anchor plate is placed midway between ground surface and the lower anchor plate. The factors <i>F_q</i> and <i>F_y</i>, on the other hand, for a group of two anchors are found to remain almost equal to that of a single isolated anchor as long as the levels of the lower plate in the group and the single isolated anchor are kept the same.

Horizontal Pullout Resistance for a Group of Two Vertical Plate Anchors in Clays

The horizontal pullout capacity of a group of two rigid strip plate anchors embedded along the same vertical plane in clays, under undrained condition, has been determined. An increase of cohesion with depth has also been incorporated. The analysis has been performed by using an upper bound finite element limit analysis in combination with linear optimization. For different clear spacing (S) between the anchors, the efficiency factor (ηcγ) has been determined to evaluate the group failure load for different values of (1) embedment ratio (H/B), (2) the normalized rate (m) which accounts for a linear increase of cohesion with depth, and (3) normalized unit weight (γH/co). The magnitude of the group failure load (1) becomes maximum corresponding to a certain spacing (Scr) between the anchors, and (2) increases with an increase in the γH/co up to a certain value before attaining a certain maximum magnitude. The value of Scr/B has been found to vary generally between 0.7 and 1.2. The maximum magnitude of ηcγ, associated with the critical spacing, (1) increases generally with increases in H/B, and (2) decreases with an increase in m. For a greater spacing between the anchors, the analysis reveals the development of a local shear zone around the lower anchor plate. The numerical results developed are expected to be useful for purpose of design.