Jyant Kumar

Indian Institute of Science Bangalore | IISC · Department of Civil Engineering

The ultimate bearing capacity of a strip footing placed horizontally over the edge of a sloping rock mass has been determined on the basis of the stress characteristics method (SCM) using the generalized Hoek–Brown yield criterion. The effect of footing–rock interface roughness on the results has also been analyzed. The problem has been solved, in...

Non-destructive evaluation of rigid pavements is of critical importance from quality assurance as well as maintenance perspective. This research is aimed at providing a framework for surface wave testing of rigid pavements by studying their dispersion characteristics and developing a strategy to back-compute upper as well as lower layers' propertie...

By using the complex variable approach, an analytical solution for non-uniformly deforming twin circular tunnels has been determined for a linear elastic weighty medium under the influence of earthquake pseudo-static inertial force. The non-uniform radial displacements along both the tunnels’ peripheries have been imposed by using the Gaussian dist...

Three-dimensional stability analysis of a vertical excavation, reinforced with grouted horizontal nails, has been carried out by using the three dimensional lower and upper bounds based finite elements limit analysis (FELA) using Optum G3. The nail along with the surrounding grouted cementitious material is assumed to behave as a single monolithic...

An approach has been proposed to assess the quality of the dispersion plot extracted from the dispersion image obtained based on the multichannel analysis of the surface waves (MASW) technique. The variation of the quality factor Q associated with a given mode has been presented as a function of frequency. A sensitivity analysis has also been perfo...

Lamb and Rayleigh waves-based dispersion analysis has been carried out for non-destructive surface wave testing of different slab-like structures involving a concrete roof slab, a concrete floor, a concrete pavement, and an asphaltic pavement. An impact was generated by gently striking the slab’s free surface with a hammer. A method has also been g...

A closed-form analytical solution using complex variables has been determined to predict ground displacements and stresses around a non-uniformly deforming single circular tunnel in a linearly elastic weightless and ponderable (weighty) medium. For the weightless medium, the solution has been derived with the satisfaction of (1) stress-free conditi...

A numerical study has been conducted to compute the ultimate bearing capacity of the embedded strip and circular footing placed on loose sand, which is densified in the upper region as well as reinforced with a geogrid sheet at the interface of loose and dense sand layers. The analysis was carried out using the lower and upper bound finite elements...

The bearing capacity factors for a rough strip footing placed on rock media, which is subjected to pseudo-static horizontal earthquake body forces, have been determined using the lower bound finite element limit analysis in conjunction with the power cone programming (PCP). The rock mass is assumed to follow the generalized Hoek-Brown (GHB) yield c...

The present study examines the stability of an embankment of cohesive-frictional material placed over a purely cohesive stratum reinforced by means of uniformly spaced vertical granular cylindrical columns. By using the kinematic yield homogenization concept, the macroscopic yield strength envelope associated with the reinforced clay layer has been...

The effect of interface friction angle between the footing and underlying soil mass on the bearing capacity factor Ng was examined by using the upper bound limit analysis, finite elements, and linear programming. The analysis was carried out by employing velocity discontinuities along all the interfaces of the chosen triangular elements. The develo...

An attempt has been made to examine numerically, based on an elasto-plastic finite elements (FE) analysis, soil unit weight-ground displacement response due to laying of single and twin circular tunnels which are supported by an internal isotropic pressure (σi); the case σi= 0 implies an unsupported tunnel. The soil mass has been assumed to be line...

By using the lower bound finite elements limit analysis, this paper presents a methodology to evaluate the bearing capacity of piles in cohesive soils. The non-homogeneous nature of soil has been assumed for which the cohesion increases linearly with depth. An axisymmetric formulation, comprising of a planar domain with a mesh of three noded triang...

Finite element-based upper bound and lower bound limit analysis are found to be an excellent tool for solving various stability structural problems with less computational cost. The accuracy and efficiency of the obtained solution is highly dependent on the intensity of elements in the high stress or stain gradient region. Therefore, an adaptive me...

The ultimate bearing capacity of a ring footing on loose sand deposit, with an inclusion of a dense sand layer on its top, has been determined numerically in a bound form by following the finite element limit analysis (FELA). The friction angles ϕ1 and ϕ2 were varied from 40° to 46° and 30° to 36° for the top dense sand and the bottom loose sand re...

This study introduces a methodology to solve plane strain stability problems in rock mechanics, following the generalized Hoek and Brown yield criterion, by employing the lower bound finite elements limit analysis in conjunction with the power cone programming. The efficacy of the proposed approach has been demonstrated by solving three different t...

While performing the upper bound limit analysis, using an associated flow rule, the expressions for the power dissipation function corresponding to different forms of yield criteria for clays exhibiting shear strength anisotropy and transversely asymmetric properties (implying different strengths in compression and tension), have been derived in te...

This study examines the stability of a single and twin horse-shoe shaped unlined tunnels laid in rock media and loaded with surcharge pressure on ground surface. The tunnels are assumed to be sufficiently long so that the plane strain analysis remains applicable. The failure of rock mass is governed by the generalized Hoek-Brown (GHB) yield criteri...

The stability of vertical unsupported circular excavations in rock media, obeying generalized Hoek‐Brown yield criterion, has been investigated by using the lower bound finite elements limit analysis. An axisymmetric analysis, composed of a planar domain with a mesh of three‐noded triangular elements, has been carried out. The optimization problem...

This study presents a computational methodology for solving axisymmetric stability problems in rock mechanics by using the finite element lower bound limit analysis. The generalized Hoek and Brown (GHB) yield criterion, which is often recommended to define failure in the intact and jointed rock mass, has been employed. No assumption(s) are required...

Bearing capacity of rectangular foundations, with varying aspect ratios (1 ≤ L/B ≤ 5) and embedded at shallow to medium depths (D/B ≤ 5), has been evaluated by using the three-dimensional cell-based smoothed finite elements quasi-kinematic limit analysis. The results have also been obtained for circular and strip foundations by performing exclusive...

Finite element based upper bound and lower bound limit analysis are found to be an excellent tool for solving various stability structural problems with less computational cost. The accuracy and efficiency of the obtained solution is highly dependent on the intensity of elements in the high stress or stain gradient region. Therefore an adaptive mes...

Different smoothed finite elements (S-FE) approaches for the kinematic limit analysis of plane strain and plane stress problems by using three-noded triangular elements have been presented for determining the collapse loads in a material following the Mohr-Coulomb yield criterion.  Using duality in optimization theory, the resulting optimization p...

The lower- and upper-bound theorems of the limit analysis have been used in conjunction with finite elements and second-order cone programming (SOCP) for determining the bearing capacity of strip and circular skirted footings on sand. The analysis follows the Mohr- Coulomb's yield criterion and the associated flow rule; sand is not usually consider...

Identification of the arrival point of the shear wave in bender element tests is a task that can have ambiguous results. The contamination of the received shear wave signal with a weak P-wave component, which can emerge either directly from the transmitter or reflect from the side boundary, makes the judgement involved in this task dubious. The dif...

A faster computational scheme is proposed to determine multimodal dispersion plots using the stiffness matrix method (SMM) for Rayleigh wave propagation in horizontally layered ground media. The scheme decomposes the governing stiffness matrix (K) into a product of unit lower triangular matrix (L) and the upper triangular matrix (U). Accordingly, t...

Three different transformation techniques, namely, (i)w-c, (ii) w-k and (iii) tau-p, has been employed for generating multimodal dispersion images on the basis of multi-channel analysis of surface waves (MASW) data recorded in distance-time domain; here w= circular frequency, c = phase velocity, tau = time intercept, p = phase slowness (1/c) and k...

A three-dimensional kinematic limit analysis approach based on the radial point interpolation method (RPIM) has been used to compute collapse loads for rectangular foundations. The analysis is based on the Mohr-Coulomb yield criterion and the associated flow rule. It is understood that the internal plastic power dissipation function and flow rule c...

The shear moduli of cylindrical metal specimens were determined by performing resonant column tests in a torsional mode of vibration. The tests were performed on four different metals, namely (i) aluminum, (ii) brass, (iii) copper, and (iv) mild steel. Keeping the length (L) of the specimens the same, different diameters (d) were chosen to vary the...

In this study, the stability of twin circular tunnels in purely cohesive and cohesive-frictional soils was evaluated. It is assumed that the internal compressive normal pressure (σ i) required to support the tunnels, by means of lining and the anchorage system, becomes uniform (isotropic) on the tunnels' periphery. The interference effect of twin t...

The vertical uplift resistance of horizontal plate anchors embedded in sand has been computed for inclined and eccentric pullout loads. The analysis has been performed by using the lower-bound theorem of the limit analysis in combination with finite element and second-order cone programming (SOCP). The methodology is based on the Mohr–Coulomb yield...

The method of stress characteristics has been used for computing the ultimate bearing capacity of strip and circular footings placed on rock mass. The modified Hoek-and-Brown failure criterion has been used. Both smooth and rough footing-rock interfaces have been modeled. The bearing capacity has been expressed in terms of nondimensional factors Nσ...

An upper bound formulation for performing the finite element limit analysis by using semidefinite programming (SDP) for an axisymmetric stability problem involving the Mohr-Coulomb yield criterion has been presented. The SDP has an advantage that it can deal with the yield criterion directly in its native form in terms of principal stresses without...

The lower- and upper-bound finite-element limit analysis in conjunction with second-order conic programming (SOCP) was used to estimate the ultimate bearing capacity of strip and circular footings with an inclusion of a layer of dense sand over existing loose sand strata. The analysis followed the Mohr-Coulomb yield criterion and an associated flow...

The stress characteristics method (SCM) has been used to compute the bearing capacity of smooth and rough ring foundations. Two different failure mechanisms for a smooth footing, and four different mechanisms for a rough footing have been considered. For a rough base, a curvilinear non-plastic wedge has been employed below the footing. The analysis...

Resonant column tests were conducted to examine the variation in shear modulus (G) and damping ratio (D) of dry sand subjected to 10 batches of vibration cycles. Each batch increment comprised 1,000 cycles. Tests were performed by varying void ratio, confining pressures, and input driving voltage. The vibration cycles cause a continuous increment i...

The complexity involved with the phase unwrapping procedure, while performing the existing spectral analysis of surface waves (SASW) on the basis of two sensors, makes it difficult to automate and requires frequent manual judgment. As a result, this approach generally becomes tedious and may yield erroneous results. The multichannel analysis of sur...

The ultimate bearing capacity of foundations on soft clays under undrained conditions has been computed with inclusion of (i) a single vertical granular trench below a strip footing and (ii) a granular column placed below a circular footing. A lower bound plane strain and axisymmetric limit analysis, in conjunction with finite elements and an optim...

In case of irregular dispersive media, a proper analysis of higher modes existing in a dispersion plot becomes essential for predicting the shear wave velocity profile of ground on the basis of surface wave tests. In such cases, an establishment of the predominant mode becomes quite important. In the current investigation for Rayleigh wave propagat...

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-efficie...

This brief article presents a simple modification to the widely-used Kausel-Roësset Stiffness Matrix Method (SMM), and in particular to its implementation in the context of the Thin-Layer Method (TLM). This modification allows making fast and accurate computations of wavenumber spectra even for layered media underlain by infinitely deep half-spaces...

The axisymmetric lower bound finite elements limit analysis technique has been used for computing the stability numbers (γH/c0) for an unsupported circular vertical excavation in the presence of surcharge pressure (q). The numerical results are presented for various combinations of H/b, ϕ, m and q; the factor m incorporates the rate of linear incre...

Resonant column tests, corresponding to a given input voltage of the drive mechanism, were conducted in torsional mode to examine the effect of vibration cycles on shear modulus (G) and damping (D) of dry sand with shear strain amplitude in a range of 0.0005-0.05%. Two different relative densities, approximately 61 and 85%, and effective confining...

By incorporating the diameter (size) effect of a conical footing, the factor Nγ has been computed. The analysis has been performed by using the lower bound theorem of limit analysis in combination with finite elements and linear optimization. By using an iterative procedure, the dependency of peak friction angle (ϕ) on mean stress (σm) has been inc...

The 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 differ...

By using six 4.5 Hz geophones, surface wave tests were performed on four different sites by dropping freely a 65 kg mass from a height of 5 m. The receivers were kept far away from the source to eliminate the arrival of body waves. Three different sources to nearest receiver distances (S), namely, 46 m, 56 m and 66 m, were chosen. Dispersion curves...

The ultimate bearing capacity of a circular footing, placed over rock mass, is evaluated by using the lower bound theorem of the limit analysis in conjunction with finite elements and nonlinear optimization. The generalized Hoek-Brown (HB) failure criterion, but by keeping a constant value of the exponent, α=0.5, was used. The failure criterion was...

The bearing capacity of a circular footing lying over fully cohesive strata, with an overlaying sand layer, is computed using the axisymmetric lower bound limit analysis with finite elements and linear optimization. The effects of the thickness and the internal friction angle of the sand are examined for different combinations of cu/(γb) and q, whe...

Experimental and numerical investigations have been carried out to determine the vertical uplift resistance of circular anchor plates embedded in cohesionless soil media. Experimental studies are performed on model circular anchor plates placed at different depths in loose to medium dry sand deposit for two different relative densities, namely, 25%...

The arrival times of primary (P) and shear (S) waves in dry sand were measured by using extender and bender elements. A series of laboratory tests were performed at five different frequencies, varying between 1 and 10 kHz, in loose and dense sands for three different confining pressures. While determining the times of arrival of both P- And S-waves...

The vertical uplift resistance of interfering pipelines buried in sands has been computed using the lower-bound limit analysis in conjunction with finite elements and nonlinear optimization. The soil mass is assumed to follow the Mohr-Coulomb failure criterion and an associated flow rule. It is specified that all the pipes fail simultaneously at th...

Vertical uplift resistance of strip and circular horizontal plate anchors embedded in soft clay with an overlay of a sand layer has been computed by using plane strain and axisymmetric lower bound limit analysis in conjunction with finite elements and linear optimization. The improvement in the magnitude of the uplift resistance, with an overlay of...

Bearing capacity factors because of the components of cohesion, surcharge, and unit weight, respectively, have been computed for smooth and rough ring footings for different combinations of ri/ro and ϕ by using lower and upper bound theorems of the limit analysis in conjunction with finite elements and linear optimization, where ri and ro refer to...

Bearing capacity factors, Nc, Nq, and Nγ, for a conical footing are determined by using the lower and upper bound axisymmetric formulation of the limit analysis in combination with finite elements and optimization. These factors are obtained in a bound form for a wide range of the values of cone apex angle (β) and ϕ with δ = 0, 0.5ϕ, and ϕ. The bea...

This paper presents a lower bound limit analysis approach for solving an axisymmetric stability problem by using the Drucker–Prager (D–P) yield cone in conjunction with finite elements and nonlinear optimization. In principal stress space, the tip of the yield cone has been smoothened by applying the hyperbolic approximation. The nonlinear optimiza...

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...

By using the lower-bound theorem of the limit analysis in conjunction with finite elements and nonlinear optimization, bearing-capacity factors, Nc and Nγq, with an inclusion of pseudostatic horizontal seismic body forces, have been determined for a shallow embedded horizontal strip footing placed on sloping ground surface. The variation of Nc and...

A method is presented for determining the ultimate bearing capacity of a circular footing reinforced with a horizontal circular sheet of reinforcement placed over granular and cohesive-frictional soils. It was assumed that the reinforcement sheet could bear axial tension but not the bending moment. The analysis was performed based on the lower-boun...

Following the recent work of the authors in development and numerical verification of a new kinematic approach of the limit analysis for surface footings on non-associative materials, a practical procedure is proposed to utilize the theory. It is known that both the peak friction angle and dilation angle depend on the sand density as well as the st...

An 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 v...

The uplift resistance of pipelines buried in sands, in the presence of inclined groundwater flow, considering both upward and downward flow directions, has been determined by using the lower bound finite elements limit analysis in conjunction with nonlinear optimization. A correction factor (fγ), which needs to be multiplied with the uplift factor...

By using the von Mises yield criterion, a numerical formulation has been proposed for solving an axisymmetric stability problem with the usage of the lower bound limit analysis, finite elements and nonlinear optimisation. The proposed formulation has been employed for computing the bearing capacity factor Nc for an axially loaded circular footing i...

A lower-bound limit analysis formulation, by using two-dimensional finite elements, the three-dimensional Mohr-Coulomb yield criterion, and nonlinear optimization, has been given to deal with an axisymmetric geomechanics stability problem. The optimization was performed using an interior point method based on the logarithmic barrier function. The y...

The vertical uplift resistance of long pipes buried in sands and subjected to pseudostatic seismic forces has been computed by using the lower-bound theorem of the limit analysis in conjunction with finite elements and nonlinear optimization. The soil mass is assumed to follow the Mohr-Coulomb failure criterion and an associated flow rule. The fail...

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...

The 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...

The ultimate bearing capacity of a circular footing, placed over a soil mass which is reinforced with horizontal layers of circular reinforcement sheets, has been determined by using the upper bound theorem of the limit analysis in conjunction with finite elements and linear optimization. For performing the analysis, three different soil media have...

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 (Sn) have been generated for both (1) cohesive-frictional soi...

The pullout capacity of an inclined strip plate anchor embedded in sand has been determined by using the lower bound theorem of the limit analysis in combination with finite elements and linear optimization. The numerical results in the form of pullout factors have been presented by changing gradually the inclination of the plate from horizontal to...

A numerical formulation has been proposed for solving an axisymmetric stability problem in geomechanics with upper bound limit analysis, finite elements, and linear optimization. The Drucker-Prager yield criterion is linearized by simulating a sphere with a circumscribed truncated icosahedron. The analysis considers only the velocities and plastic...

A series of spectral analyses of surface waves (SASW) tests were conducted on a cement concrete pavement by dropping steel balls of four different values of diameter (D) varying between 25.4 and 76.2 mm. These tests were performed (1) by using different combinations of source to nearest receiver distance (S) and receiver spacing (X), and (2) for tw...

The stability of a long circular tunnel in a cohesive frictional soil medium has been determined in the presence of horizontal pseudo-static seismic body forces. The tunnel is supported by means of lining and anchorage system which is assumed to exert uniform internal compressive normal pressure on its periphery. The upper bound finite element limi...

The 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...

This paper presents a simple technique for reducing the computational effort while solving any geotechnical stability problem by using the upper bound finite element limit analysis and linear optimization. In the proposed method, the problem domain is discretized into a number of different regions in which a particular order (number of sides) of th...

A 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 limi...

By incorporating the variation of peak soil friction angle (phi) with mean principal stress (sigma(m)), the effect of pipe diameter (D) on the vertical uplift resistance of a long horizontal pipeline embedded in sand has been investigated. The analysis has been performed by using the lower bound finite-element limit analysis in combination with non...

A number of spectral analysis of surface waves tests were performed on asphaltic concrete pavement. These tests were performed by dropping steel balls on the pavement surface for different combinations of source to first receiver distance and receiver spacing. Four different values of ball's diameter, namely, 25·4 mm, 38·1 mm, 50·8 mm, and 76·2 mm,...

By using the upper bound finite‐elements limit analysis, with an inclusion of single and two horizontal layers of reinforcements, the ultimate bearing capacity has been computed for a rigid strip footing placed over (i) fully granular, (ii) cohesive‐frictional, and (iii) fully cohesive soils. It is assumed that (i) the reinforcements are structural...

The vertical uplift resistance of two closely spaced horizontal strip plate anchors has been investigated by using lower and upper bound theorems of the limit analysis in combination with finite elements and linear optimization. The interference effect on uplift resistance of the two anchors is evaluated in terms of a nondimensional efficiency fact...

The horizontal pullout capacity of a group of two vertical strip anchors placed along the same vertical plane in sand has been determined by using the upper bound finite elements limit analysis. The variation of the efficiency factor (ξ γ ) with changes in clear spacing (S) between the anchors has been established to evaluate the total group failur...

By applying the lower bound theorem of limit analysis in conjunction with finite elements and nonlinear optimization, the bearing capacity factor Nγ has been computed for a rough strip footing by incorporating pseudostatic horizontal seismic body forces. As compared with different existing approaches, the present analysis is more rigorous, because...

The ultimate bearing capacity of strip foundations in the presence of inclined groundwater flow, considering both upward and downward flow directions, has been determined by using the lower bound finite-element limit analysis. A numerical solution has been generated for both smooth and rough footings placed on frictional soils. A correction factor...

By using the lower-bound finite element limit analysis, the stability of a long unsupported circular tunnel has been examined with an inclusion of seismic body forces. The numerical results have been presented in terms of a non-dimensional stability number (γH/c) which is plotted as a function of horizontal seismic earth pressure coefficient (k h)...

A series of resonant column tests have been performed in the torsional mode of vibration to assess the effect of saturation, starting from the near dry state to the fully saturated state, on the damping ratio of sands corresponding to the threshold strain level. Tests were carried out on three different gradations of sand for various combinations o...

The stability of two long unsupported circular parallel tunnels aligned horizontally in fully cohesive and cohesive-frictional soils has been determined. An upper bound limit analysis in combination with finite elements and linear programming is employed to perform the analysis. For different clear spacing (S) between the tunnels, the stability of...

The horizontal pullout capacity of a group of two vertical strip plate anchors, placed along the same vertical plane, in a fully cohesive soil has been computed by using the lower bound finite element limit analysis. The effect of spacing between the plate anchors on the magnitude of total group failure load () has been evaluated. An increase of so...

By using the axisymmetric quasi-lower bound finite-element limit analysis, the bearing capacity factors Npc and Npγq have been computed for axially loaded piles, with the shaft embedded in a fully cohesive soil medium and the tip placed over cohesive frictional soil strata. The results were obtained for various combinations of L/D, φl, and cl/cu; t...

SUMMARY A rigorous lower bound solution, with the usage of the finite elements limit analysis, has been obtained for finding the ultimate bearing capacity of two interfering strip footings placed on a sandy medium. Smooth as well as rough footing–soil interfaces are considered in the analysis. The failure load for an interfering footing becomes alw...

The linearization of the Drucker-Prager yield criterion associated with an axisymmetric problem has been achieved by simulating a sphere with the truncated icosahedron with 32 faces and 60 vertices. On this basis, a numerical formulation has been proposed for solving an axisymmetric stability problem with the usage of the lower-bound limit analysis...

By incorporating a variation in soil internal friction angle ϕ with mean principal stress σm, the dependency of bearing capacity factor Nγ with footing diameter B has been evaluated for circular footings. The evaluation has been performed by a lower bound finite element limit analysis in combination with a linear optimization. Two ϕ–σm curves, avai...