Papers by Lysandros Pantelidis
An Analytical Method for Designing Embedded Retaining Walls
Atlantis highlights in engineering, Dec 31, 2022
An Analytical Method for Designing Laterally Loaded Piles
Atlantis highlights in engineering, Dec 31, 2022
An Analytical Method for the Calculation of the Shaft Resistance of Axially Loaded Piles in Cohesive-Frictional Soils
Atlantis highlights in engineering, Dec 31, 2022
The Generalized Coefficients of Earth Pressure: Numerical Validation and Comparison with Eurocode 8-5 Method
Advances in Science, Technology & Innovation/Advances in science, technology & innovation, 2024
Study on characterization, mechanical, and thermal properties of Alfa fiber–reinforced compressed earth blocks incorporating crushed brick waste
Arabian Journal of Geosciences
Archives of computational methods in engineering, Jun 18, 2024
This paper provides a comprehensive review on the effect of load inclination and eccentricity on ... more This paper provides a comprehensive review on the effect of load inclination and eccentricity on the bearing capacity of shallow foundations. Regarding load eccentricity, Meyerhof's intuitive formula B� = B -2e b aligns well with finite ele- ment analyses, though it is slightly conservative. Analysis using finite element results revealed the more accurate formula B -1.9e b . Concerning load inclination factors, numerous such factors exist in the literature. However, most are either intuitive or derived from small-scale experimental results, rendering them unreliable due to the significant impact of model scale on the bearing capacity of footings. Based on numerical results, it is proposed that all inclination factors (namely i c , i and i q ) can be reliably expressed by a formula of the form 1 -f 1 ⋅ tan f 3 f 2 , where is the inclination angle of the loading with respect to the vertical, f 1 and f 3 are coefficients and f 2 = 3 . The latter ensures smooth transition from the bearing capacity failure to the sliding failure as increases. It is also observed that many i-factors in the literature and various design stand- ards employ an impermissible combination of sliding resistance at the footing-soil interface and Mohr-Coulomb bearing capacity failure under the footing. Moreover, it is shown that only the i c factor depends on the angle of internal friction of soil. Finally, Vesic's 1975 "m" interpolation formula largely falls short in accurately representing the effect of the direction of the horizontal loading.
International Journal for Numerical and Analytical Methods in Geomechanics, Jul 24, 2012
A closed-form solution (CFS) satisfying both equilibrium of moments and forces for the stability ... more A closed-form solution (CFS) satisfying both equilibrium of moments and forces for the stability analysis of earth slopes in 2D is proposed. The sliding surface is assumed circular and treated as a rigid body, allowing the internal state of stress to be ignored. The proposed solution can be applied to both homogenous and nonhomogenous slopes of either simple or complex geometry, and can also deal with any kind of additional loading. The method is based on the fact that, all possible forces acting on the slope can be projected onto the failure surface where they are broken into driving and resisting ones. Comparison of the safety factors obtained by the proposed CFS and those obtained by traditional limit equilibrium methods, as applied to several test examples, indicates that the proposed method is more conservative, whereas moreover, it gives a more realistic point of view for the formation of tension crack in slopes.
Research Square (Research Square), May 22, 2023
Since Terzaghi introduced his bearing capacity equation with the three −factors in 1943, numerous... more Since Terzaghi introduced his bearing capacity equation with the three −factors in 1943, numerous bearing capacity methods have been proposed in the literature. However, the methods proposed by Terzaghi (T), Meyerhof (M), Hansen (H) and Vesic (V) are the most widely adopted. Also, while various design codes show a preference for Vesic's −factors, there is no consensus on depth factors. In this paper, the aforementioned four classical methods, as well as the methods included in EN1997-1:2004, prEN1997-3:2023 (draft standard), API, AASHTO, Geotechnical Engineering Office, IS6483:1981 and FHWA-SA-02-054 design standards are compared against finite elements. The focus is on the effectiveness of depth factors, which essentially account for errors associated with analytical modeling, that is, with the −factors. The analysis reveals that for the case of effective stress analysis with = (indicating soils adhering to the associated flow rule), IS6483:1981 provides the more satisfactory predictions (IS6483:1981 combines Vesic's −factors with Meyerhof's depth factors). For the case of total stress analysis, Meyerhof's method is superior to the other methods. Also for the case of effective stress analysis but for the = 0 case (indicating soils adhering to the non-associated flow rule), the AASHTO (and FHWA as well) approach is preferable; AASHTO uses Hansen's factor, while = = 1. Based on the aforementioned lack of consensus and on the fact that the rigidity of footings is an additional factor influencing bearing capacity, the author conducted extensive finite element analysis to identify suitable depth factors. The analysis clearly shows that, a single depth factor of the form (+ • ⁄) can effectively replace the set of depth factors associated with the three bearing capacity equation terms, increasing accuracy, and simplifying the whole procedure. Based on the finite element analysis results and regression analysis, and values are proposed for both effective and total stress analysis, = and 0, as well as for rigid and flexible footings for the four classical methods (T, M, H and V). Finally, the analysis also reveals that a strong relationship exists between the bearing capacity of rigid footings and the respective one of flexible footings. This is ,Flexible ≈ 0.93 ,Rigid for either effective stress analysis with = or total stress analysis and ,Flexible ≈ ,Rigid for effective stress analysis with = 0.
Research Square (Research Square), Mar 8, 2023
There is no doubt that the problem of a laterally loaded pile is an earth pressure analysis 8 pro... more There is no doubt that the problem of a laterally loaded pile is an earth pressure analysis 8 problem, involving the flexural rigidity of the pile and the possible fixity of the pile head to a 9 pile cap. During the deformation, which is a combination of bending, rotation and horizontal 10 translation, the earth pressures may take any value between the state at-rest and the active or 11 the passive state on the two sides of the pile. The current practice, as this is depicted by the 12 various design standards, is the − method, with the soil to be replaced by an array of parallel springs. This simplification is accompanied by rough assumptions for the Winkler spring constant. Relatively, the author offers a brief, yet comprehensive, review of the more important − methods, shedding some light to their validity and highlighting the need for adopting a more rational approach. In this respect, quite recently the author proposed a continuum mechanics approach for deriving earth pressure coefficients for any soil state between the at-rest state and the active or the passive state, applicable to cohesive-frictional soils and both horizontal and vertical pseudo-static conditions. An analytical expression for the calculation of the required structure movement for the mobilization of the active or passive failure state of soil is also provided. The proposed method combines these expressions with the static analysis of elastic beams, offering complete earth pressure and pile deflection diagrams, taking also into account the inertial effect of a possible seismic event (in a pseudostatic manner), as well as the overconsolidation caused by a displacement pile to the surrounding soil. Finally, the location of the point of virtual fixity, which is an important parameter in the case of long, slender piles, is calculated following the proposed procedure. Keywords: laterally loaded piles; the Generalized Coefficient of Earth Pressure; static analysis of elastic beams; intermediate earth pressures; − method a general discussion for the − method. Regarding Broms' method, Russo and Viggiani [14, 58 15] checked the method in question by means of a database including over 50 horizontal load 59 tests on piles taken to failure and sufficiently well documented to allow a back analysis of the 60 results. Their comparison analysis shows that the vast majority of data points fall within the 61 ±40% confidence lines, symmetrically for both clays and sands, although a cloud of points lies 62 outside the-40% confidence line (conservative side) for the case of sands. 63 EN1997-1:2004 highlights the need for considering the compatibility of strains in the anal-64 ysis of laterally loaded piles (§2.4.1(13)), indicating that numerical methods can be appropriate 65
Modeling the resilient modulus of subgrade soils with a four-parameter constitutive equation
Modeling Earth Systems and Environment, Feb 20, 2023
Research Square (Research Square), May 17, 2023
The bearing capacity of shallow foundations is one of the major fields of soil mechanics and foun... more The bearing capacity of shallow foundations is one of the major fields of soil mechanics and foundation engineering. Since 1920, when Prandtl suggested the well-known failure mechanism with the three zones and 1943, when Terzaghi, based on this mechanism, suggested his famous equation with the three −factors, numerous bearing capacity methods for the basic problem of centrically-vertically loaded strip footings have been proposed in the literature, mainly focusing on better defining the factor. It is mentioned that although Terzaghi considered the vertical balance of forces, he indirectly relied on the theory of earth pressure, calculating three earth pressure coefficients (for the self-weight and cohesion of the soil and for the lateral surcharge), which worked in the vertical direction. The purpose of the present paper is to suggest a completely new approach to the above-mentioned problem. It is shown that the problem in question is a classical earth pressure analysis problem, with a virtual wall dividing the failure mass into an active and a passive Rankine failure zone. Also, it is shown that it is not the factor which prevents us from having better prediction for the bearing capacity of footings, but the various non-effective depth factors. The solution to the problem demands a unique depth factor to be applied to all three bearing capacity terms. In this paper, this depth factor derives from extensive regression analysis. Moreover, since, as known, the dilatancy of soils affects the bearing capacity value, the proposed method has been calibrated against nonassociated finite element models with = 0°. Thus, the proposed method is on the safe side.
Research Square (Research Square), Oct 25, 2022
Some equations have been given in a different form (Equation 4 and various equations in Appendix ... more Some equations have been given in a different form (Equation 4 and various equations in Appendix A).-The author noticed an error in his Excel Spreadsheet regarding the calculation of the Work Done in the example presented. This error affected some charts. In the current version this error has been corrected. The general procedure and conclusion did not change.-Correction of various minor editing issues.
Research Square (Research Square), Aug 24, 2022
According to the current practice, the unit shaft resistance of piles based on ground pa-9 ramete... more According to the current practice, the unit shaft resistance of piles based on ground pa-9 rameters is calculated with the-method or the-method, for total or effective stress con-10 ditions respectively. Indeed, these two methods are included in the prEN1997-3:2021 11 draft standard. And while the physics behind these methods is adequate for calculating the shaft resistance of piles in clays and sands for total and effective stress analysis respectively, the main difficulty in applying the effective stress approach in clays is to esti-14 mate the radial effective stress acting on the pile. In the present paper this is addressed by a proposed earth pressure at-rest coefficient, applicable to cohesive-frictional soils and both horizontal and vertical pseudo-static conditions. Comparison examples show excellent agreement of the analytically derived shaft resistance capacities with the respective numerical ones. Regarding seismic conditions it is noted that, for the case of axially loaded piles the horizontal component of the seismic excitation does not affect the shaft resistance 20 capacity of piles, while the vertical component could be neglected as acting favorably. Finally, it is mentioned that the proposed method is a general − procedure, applicable also for purely cohesive and cohesionless soils.
Stability assessment of soil slopes in three dimensions: The effect of the width of failure and of tension crack
Geomechanics and Engineering, 2020
This paper investigates the effect of the width of failure and tension crack (TC) on the stabilit... more This paper investigates the effect of the width of failure and tension crack (TC) on the stability of cohesive-frictional soil slopes in three dimensions. Working analytically, the slip surface and the tension crack are considered to have spheroid and cylindrical shape respectively, although the case of tension crack having planar, vertical surface is also discussed; the latter was found to return higher safety factor values. Because at the initiation of a purely rotational slide along a spheroid surface no shear forces develop inside the failure mass, the rigid body concept is conveniently used; in this respect, the validity of the rigid body concept is discussed, whilst it is supported by comparison examples. Stability tables are given for fully drained and fully saturated slopes without TC, with non-filled TC as well as with fully-filled TC. Among the main findings is that, the width of failure corresponding to the minimum safety factor value is not always infinite, but it is aff...
Research Square (Research Square), Feb 11, 2021
As known, in a Winkler type of analysis the soil medium underneath the foundation is violently re... more As known, in a Winkler type of analysis the soil medium underneath the foundation is violently replaced by a row of parallel springs having constant k s. For the effective calculation of the latter, which is called the modulus of subgrade reaction, the two elastic constants of the soil (the elastic modulus, E and the Poisson's ratio, m) must be known. Although for homogenous soils this generally seems not to be a problem, the same does not stand for stratified mediums or mediums with linearly increasing modulus with depth. In addition, in a Winkler type of analysis, the proper pair of elastic constant values of soil should be selected. This refers to a Poisson's ratio value equal to zero corresponding to the deformation pattern of springs (compression with no lateral expansion) and the respective modulus. In the present paper a method for calculating the equivalent elastic constants for the above mentioned mediums is proposed based on the theory of elasticity combining the principle of superposition. Various cases are considered, since the equivalent modulus, E eq , depends on the rigidity and the shape of the footing. As shown, the derived E eq values not only return reliable settlement results, but also settlement profiles that are similar to those corresponding to the original soil mediums.
Finite element and regression analysis for improving Terzaghi’s, Meyerhof’s, Hansen’s and Vesic’s bearing capacity methods for strip foundations
The bearing capacity of shallow foundations is one of the major fields in soil mechanics and foun... more The bearing capacity of shallow foundations is one of the major fields in soil mechanics and foundation engineering. Since 1943, when Terzaghi suggested his famous equation with the three N-factors, several dozens of bearing capacity methods have been proposed in the literature, mainly focusing on better defining the Nγ factor. However, the methods proposed by Terzaghi (T), Meyerhof (M), Hansen (H) and Vesic (V) remain by far the most popular ones, with the last one to be component of many contemporary design codes. In this paper, the author put these four methods into extensive comparison against the finite element method. A common characteristic of the results is the great scatter of values, while none of these methods seems to be superior to the others. The regression analysis carried out by the author, however, clearly showed that it is not Nγ that prevents us from having a reliable analytical prediction for the bearing capacity of footings, but the various depth factors. The an...
Bearing capacity of centrically-vertically loaded strip foundations based on soil parameters: a classical earth pressure analysis problem
The bearing capacity of shallow foundations is one of the major fields of soil mechanics and foun... more The bearing capacity of shallow foundations is one of the major fields of soil mechanics and foundation engineering. Since 1920, when Prandtl suggested the well-known failure mechanism with the three zones and 1943, when Terzaghi, based on this mechanism, suggested his famous equation with the three N-factors, numerous bearing capacity methods for the basic problem of centrically-vertically loaded strip footings have been proposed in the literature, mainly focusing on better defining the Nγ factor. It is mentioned that although Terzaghi considered the vertical balance of forces, he indirectly relied on the theory of earth pressure, calculating three earth pressure coefficients (for the self-weight and cohesion of the soil and for the lateral surcharge), which worked in the vertical direction. The purpose of the present paper is to suggest a completely new approach to the above-mentioned problem. It is shown that the problem in question is a classical earth pressure analysis problem,...
Finite element and regression analysis for improving Terzaghi’s, Meyerhof’s, Hansen’s and Vesic’s bearing capacity methods
The bearing capacity of shallow foundations is one of the major fields in soil mechanics and foun... more The bearing capacity of shallow foundations is one of the major fields in soil mechanics and foundation engineering. Since 1943, when Terzaghi suggested his famous equation with the three N-factors, several dozens of bearing capacity methods for centrically-vertically loaded strip footings have been proposed in the literature, mainly focusing on refining the Nγ factor. However, these proposed by Terzaghi, Meyerhof, Hansen and Vesic remain by far the most popular ones, with the last one to be component of many contemporary design codes. In this paper, the author put these four methods into extensive comparison against the finite element method. From the results it is clear that the scatter of values is a common characteristic, while none of these methods is superior to the others. During the last 100 years, Nγ was either a demon needing exorcise or a scapegoat. The regression analysis carried out by the author, however, clearly showed that it is not Nγ that prevents us from having a ...
Elastic and Consolidation Settlement Analysis of Rigid Footings Relying on the “Characteristic Point”
Geotechnical and Geological Engineering
Applied Sciences
Improving the mechanical properties of low-strength soils (e.g., high plasticity clays) is one of... more Improving the mechanical properties of low-strength soils (e.g., high plasticity clays) is one of the main branches of geotechnical engineering. The adoption of stabilization techniques for ensuring that structures will be founded on an adequately strong soil base is a common practice. Stabilization techniques for clay soils may include inert materials (cohesionless soils), chemical substances (cement, lime, or industrial additives), or the use of randomly distributed fibers. While all of these additives are added to low-strength soils by mixing, the question remains whether an optimal combination of stabilization techniques can be achieved for maximizing soil strength. Besides, each one of these additives contributes to an increase in soil strength in a different manner (soil replacement, chemical bonding of soil particles, and soil reinforcement respectively), while, according to the literature, each technique has its limitations. The latter refers to a limited effect on strength ...
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Papers by Lysandros Pantelidis