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Stone columns are a popular formof ground improvement that can be applied to a variety of foundation solutions involving soft soil deposits. Many design methods are based on an assumption that columns with a length-to-diameter ratio greater than 4 bulge uniformly along their length. This mode of deformation is not valid for small groups of columns in which interaction between individual columns and the footing gives rise to more complex behavior. The deformational behavior of stone columns at serviceability limit state is of utmost importance, because settlement rather than bearing capacity criteria are generally more onerous in soft soils. The results of some high-quality laboratory studies have been informative in this respect, but the extrapolation of results from small-scale tests comes with the caveats associated with single-gravity laboratory testing. The FEM, in combination with advanced constitutive models, can provide a link between the deformational behavior and settlement performance of discrete column groups at working stress levels. A series of analyses was conducted to examine the influence of key design parameters such as column length, spacing, and the number of columns. The influence of a stiff crust was also examined, because the reference soil profile adopted for these analyses was that of the well-characterized Bothkennar test site. The following three modes of deformation were identified by examining the distribution of stress and strain within columns and the surrounding soil: individual punching, block punching, and bulging. Individual and block punching developed in short or closely spaced columns, whereas block punching was more prevalent in larger groups. Bulging develops in long, widely spaced columns and generally occurs at the point of lowest lateral restraint. In addition, novel parameters referred to as compression and punching ratios were developed to validate the in-depth analysis and identify the principal design parameters that influence the behavior of small groups of stone columns. The results indicate that the mode of deformation is governed by column spacing and length rather than the number of columns. This finding is important, because it indicates that settlement design methods that are developed for large groups of columns are applicable to discrete groups at similar spacings and lengths. It was also observed that the influence of the stiff crust forces bulging to occur deeper and might have led authors in the past to suggest the existence of a critical length. [ABSTRACT FROM AUTHOR]

Monopiles are the most commonly used foundation type for offshore wind turbine (OWT) structures and are characterized by relatively large geometric dimensions, compared with offshore pile foundations typically used in the oil and gas industries. To date, there are no established technical guidelines tailored for the design and analysis of OWT monopiles. This paper first identifies various intrinsic drawbacks involved with the existing design and analysis methodologies as applied to OWT monopiles. Next, a comprehensive experimental program of 1g repeated lateral load tests, performed on a scaled rigid monopile installed in dry sand beds, is presented to investigate its behavior under various loading scenarios. The experimental results provide insights into the various blurry issues in the existing literature related to monopile behavior under long-term repeated lateral loading. Lateral soil resistance profiles were determined from the measured pile bending strain data and found to be markedly dependent on the degree of the polynomial function used for curve-fitting of the bending strain data. Finally, an experimental model is presented for estimation of the pile's accumulated rotation, which takes into account various basic characteristics of the applied lateral load cycles. [ABSTRACT FROM AUTHOR]

Two geotechnical centrifuge tests were designed to elicit the influence of soil-foundation-structure interaction (SFSI) and structure-soil-structure interaction (SSSI) effects on the seismic demands of an inelastic frame structure founded on individual spread footings. Four experimental cases were considered: (1) SFSI of an individual inelastic frame structure (baseline case); (2) in-plane SSSI between the frame structure and a large elastic wall structure designed to respond predominately in a rocking mode; (3) anti-plane SSSI between the frame and wall structures; and (4) combined in-plane and anti-plane SSSI between the frame structure and two wall structures. Results from Cases 1, 2, and 4 are analyzed considering 13 demand parameters. The peak seismic demands from the baseline case are compared to the peak demands from the SSSI cases to elicit the impacts of building adjacency. The number of earthquake motions that resulted in increases or decreases in the seismic demands in the frame structure are tracked for the SSSI cases. For these tests, SSSI consistently results in increased peak foundation moment and foundation base shear demands, regardless of the geometric layout of the structures. These increases propagate throughout the superstructure, resulting in increases in moment, shear and curvature ductility demands in the structural components. SSSI effects are observed to be most significant for low-to-moderate intensity earthquake motions, suggesting that particular consideration should be given to the likelihood of SSSI for highly probable earthquakes. [ABSTRACT FROM AUTHOR]

Conventional bearing capacity analyses for shallow foundations placed on slopes use a modified set of bearing capacity factors based on soil properties, footing geometry, and slope configuration, but are restricted to purely cohesionless or purely cohesive soils. This approach is adequate for establishing bearing capacity on engineered fills with controlled foundation properties, yet does not adequately address design for bearing capacity on soils that have both cohesion and internal frictional resistance--a common scenario for native soils. This role becomes increasingly important in design for mechanically stabilized earth walls, which are often placed on slopes of native c'-φ' soils in which the bearing capacity can often be the critical design constraint. Prior approaches to bearing capacity on horizontal ground for c'-φ' soils utilize principles of limited state plasticity in their formulation, yet the most commonly applied bearing capacity approaches on slopes use semiempirical formulations that employ mutually exclusive soil strength parameters. In this work, results are attained using upper-bound limit state plasticity failure discretization scheme, known as discontinuity layout optimization (DLO), which uses nonassumptive failure geometry (under translational kinematics) in its formulation. The values presented demonstrate important components in consideration of bearing capacity for strip footings placed adjacent to slopes of c'-φ' soils, in particular, the relationship between soil strength properties, slope height to footing width ratio, slope angle, and critical collapse mechanism. A set of reduction coefficients that can be directly applied to the classical bearing capacity formulation is presented for ease of application. [ABSTRACT FROM AUTHOR]

This article presents the findings of an investigation that used finite-element analysis to determine the influence of a concrete footing's dimensions on its temperature development and cracking at early age. A three-dimensional finite-element model was used to predict temperatures in the footing and to assess cracking potential of the concrete. A parametric study consisting of 63 finite-element analyses was conducted on three different footing shapes: (1) a cubic shape, (2) a length:width:depth ratio of 4:4:1, and (3) a length:width:depth ratio of 4:2:1. Volume-to-surface area ratios () ranged from 0.33 to 4.0 m. The results showed that cracking potential does not depend on a footing's dimensions when its is 1.3 m or greater. Rectangular footings that have the same but different shapes (dimensional proportions) developed a similar maximum temperature, a similar maximum temperature differential, and a similar minimum crack index under the same insulation condition. Smaller footings allowed slightly higher maximum temperature differential before thermal cracking occurred. [ABSTRACT FROM AUTHOR]

This paper presents an experimental study of the behavior of an eccentrically loaded model ring footing resting on a compacted replaced layer of sand that overlies an extended layer of loose sand. Particular emphasis is placed on the potential benefits of reinforcing the replaced sand layer with geogrid reinforcement. Load configuration was designed to simulate ring footings under vertical loads and overturning moment caused by lateral loads. Several configurations of geogrid layers, number, and stiffness were used to study ring footings with different inner-to-outer-diameter ratios and load eccentricities. The effect of the depth and the relative density of the replaced sand layer was also investigated. Test results indicate that the behavior of an eccentrically loaded ring footing significantly improves with an increase in the depth and the relative density of the replaced compacted sand layer. However, the inclusion of soil reinforcement not only leads to a significant reduction in the depth of the replaced sand layer but also causes a considerable increase in the bearing capacities of the eccentrically loaded rings, leading to the cost-effective design of the footings. On the basis of the test results, the effects of different parameters are presented and discussed. [ABSTRACT FROM AUTHOR]

A foundation system may involve more than a single footing with an arrangement such that the footings are sufficiently closely spaced that adjacent footings interact. Vertical, horizontal, and moment capacity of multifooting foundation systems are potentially dependent on footing interaction, and in particular overturning capacity can be significantly enhanced by the structural rigidity of a multifooting foundation system. There is no established procedure for the calculation of bearing capacity of a shallow foundation system comprising cojoined footings and ad hoc approaches may simply involve summing the ultimate limit states of the individual footings as if they acted independently; neglecting additional capacity of the system available from the kinematic constraint provided by the structural connection between the footings. Plane strain finite-element analyses have been carried out to investigate the undrained ultimate limit states under general loading of skirted two-footing foundation systems at various normalized spacing compared to a single skirted footing of equal bearing area and embedment ratio. [ABSTRACT FROM AUTHOR]

The purpose of this study was to critically examine insitu test methods as a means for predicting settlement of shallow foundations. Accordingly, a 1.8 m(6 ft) diameter concrete footing was statically load tested. Prior to construction, insitu [standard penetration test (SPT), cone penetration test (CPT), dilatometer (DMT), and pressuremeter (PMT)] and laboratory tests were performed to determine engineering properties of the soil. Predictions of the footing settlement were made by traditional as well as finite element methods. The results of the static load test showed settlements were over predicted by all methods. However, the traditional methods provided reasonable settlement estimates using either SPT-N or back computed CPT(N) as input. Finite element analyses using either DMT or CPT derived input parameters provided reasonable settlement estimates. Finite element analyses using SPT or PMT derived input parameters provided poor settlement estimates. The Mohr–Coulomb (elastoplastic) model, accounting for overconsolidation, provided better estimates than the hardening soil (hyperbolic-cap) model for all insitu test derived parameters. [ABSTRACT FROM AUTHOR]

There is no established procedure for the calculation of bearing capacity of a shallow foundation system comprising cojoined footings. Ad hoc approaches are relied on and may simply involve summing the ultimate limit states of the individual footings as if they acted independently; neglecting additional capacity of the system available from the kinematic constraint provided by the structural connection between the footings. In this study, the undrained capacity under general loading of rigidly connected two-footing systems at various separations has been investigated with finite-element analyses. Results are presented in terms of ultimate limit states under pure vertical (V), horizontal (H), and moment (M) loading, and failure envelopes defining limiting load states under combined VH, VM, HM, and VHM loads. Kinematic failure mechanisms observed in the finite-element analyses are presented and in cases used to provide the basis for upper bound solutions. [ABSTRACT FROM AUTHOR]

The effect of interface friction angle (δ) between the footing and underlying soil mass on the bearing capacity factor Nγ 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 development of the plastic strains within elements was incorporated by using an associated flow rule. It was clearly noted that an increase in δ leads to a continuous increase in Nγ. With δ=[lowercase_phi_synonym], the magnitude of Nγ becomes almost the same as that for a perfectly rough foundation, that is, when no slippage takes place between the footing and underlying soil mass. The size of the plastic zones increases with increase in δ and [lowercase_phi_synonym]. The obtained values of Nγ, for perfectly smooth and perfectly rough footings, compare quite favorably with those reported in literature. The study demonstrates that in the case when δ is smaller than [lowercase_phi_synonym], the assumption of a perfectly rough footing will lead to an unsafe prediction of the ultimate bearing capacity. [ABSTRACT FROM AUTHOR]

The effect of interface friction angle (δ) between the footing and underlying soil mass on the bearing capacity factor Nγ 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 development of the plastic strains within elements was incorporated by using an associated flow rule. It was clearly noted that an increase in δ leads to a continuous increase in Nγ. With δ=[lowercase_phi_synonym], the magnitude of Nγ becomes almost the same as that for a perfectly rough foundation, that is, when no slippage takes place between the footing and underlying soil mass. The size of the plastic zones increases with increase in δ and [lowercase_phi_synonym]. The obtained values of Nγ, for perfectly smooth and perfectly rough footings, compare quite favorably with those reported in literature. The study demonstrates that in the case when δ is smaller than [lowercase_phi_synonym], the assumption of a perfectly rough footing will lead to an unsafe prediction of the ultimate bearing capacity. [ABSTRACT FROM AUTHOR]

The ultimate bearing capacity of two interfering strip footings was determined by using the method of stress characteristics. The analysis was performed by choosing two different possible failure mechanisms. The variation of the efficiency factor (ξγ) was computed with respect to change in the clear spacing (s) between the two footings. For a given s/B, the value of ξγ predicted on the basis of Mechanism 1 was always found to be smaller than those on the basis of Mechanism 2. For Mechanism 1, the maximum value of ξγ, which becomes always equal to 2.0, always occurs at s/B=0. On the other hand, the Mechanism 2 provides maximum value of ξγ even greater than 2.0, especially with [lowercase_phi_synonym]>20°, corresponding to s/B=scr/B. It was noted that the results from Mechanism 2 compare more closely with the theory of Stuart in 1962 and with the recent upper bound limit analysis solution of the writers. [ABSTRACT FROM AUTHOR]

This paper addresses the problem of a circular footing of finite but nonzero stiffness embedded in an isotropic nonhomogeneous elastic half-space. The problem is solved by coupling the scaled boundary finite-element method with axisymmetric shell finite elements. The coupling of the two methods is validated by comparing computed solutions with analytical solutions for a flexible footing subjected to a uniformly distributed vertical load embedded in an elastic full-space. Based on the finding that the bending stiffness of the footing dictates the response for vertical and moment load cases, whereas the normal stiffness of the footing dominates the horizontal response, a convenient method for estimating dimensionless elastic stiffness coefficients is presented graphically. New results are presented for homogeneous and Gibson soil profiles and Poisson’s ratios of 0.2 and 0.499, to represent both sand and clay. An example demonstrating a practical application of these results is also provided. [ABSTRACT FROM AUTHOR]

This paper presents the results of laboratory model tests on the influence of soil confinement on the behavior of a model footing resting on granular soil. Confining cylinders with different heights and diameters were used to confine the sand. The ultimate bearing load of a circular footing supported on a three-dimensional confined sand bed was studied. The studied parameters include the cell height, cell diameter, the depth to the top of the cell, and the embedded depth of footing. Initially, the response of a nonconfined case was determined and then compared with that of confined soil. The results were then analyzed to study the effect of each parameter. The results indicate that the bearing load capacity of circular footing can be appreciably increased by soil confinement. It was concluded that such reinforcement resists lateral displacement of soil underneath the footing leading to a significant improvement in the response of the footing. For small cell diameters, the cell–soil footing behaves as one unit (deep foundation), while this pattern of behavior was no longer observed with large cell diameters. The recommended cell heights, depths, and diameters that give the maximum bearing capacity improvement are presented and discussed. [ABSTRACT FROM AUTHOR]

Earlier proposals for shape factors used in calculations of bearing capacity of square and rectangular footings are examined. These proposals are based on empirical data for small footings, whereas a new suggestion for these factors presented in this paper is based on the elasto-plastic model of the soil and finite element analysis. The earlier factors modifying the contribution of cohesion and overburden were found to be conservative, but acceptable in design. However, the earlier proposals for the shape factor that affects the contribution of the soil weight to the bearing capacity indicate contradictory trends, and the factor calculated in this paper is suggested as an alternative. [ABSTRACT FROM AUTHOR]

Reinforced soil is a practical solution to construction of unpaved roads or placement of footings over weak soils. A stability analysis of reinforced foundation soil is presented in this paper. A method is suggested for calculating limit loads on strip footings over foundation soils reinforced with horizontal layers of geosynthetics. Separate solutions are given for a case where reinforcement layers slip within the soil, and for a case where reinforcement ruptures. In the former case, an increase in the bearing capacity is dependent on the characteristics of the soil-reinforcement interface, whereas in the latter case it depends on the strength of the reinforcement. In both cases the increase in the limit load is dependent on the internal friction angle of the soil. Expressions are developed for quantitative predictions of bearing capacity of the foundation soil with horizontal layers of reinforcement. An optimum reinforcement depth is also given. [ABSTRACT FROM AUTHOR]

A procedure based on Kötter's equation is developed for the evaluation of bearing capacity factor Nγ with Terzaghi's mechanism. Application of Kö tter's equation makes the analysis statically determinate, in which the unique failure surface is identified using force equilibrium conditions. The computed Nγ values are found to be higher than Terzaghi's value in the range 0.25-20%, with a diverging trend for higher values of angle of soil internal friction. A fairly good agreement is observed with other solutions which are based on finite difference coupled with associated flow rule, limit analysis, and limit equilibrium. Finally, the comparison with available experimental results vis-à-vis other solutions shows that, computed Nγ values are capable of making a reasonably good prediction. [ABSTRACT FROM AUTHOR]

In practice the situation often arises where extra load needs to be added onto existing foundations. This can arise due to the installation of additional equipment in a building, or to the construction of new floors, etc. It also arises in a situation where old foundations are used for a new building, a practice likely to become increasingly popular in the future. If the foundation soil is clay, then its undrained strength would have increased with time due to the dissipation of excess pore water pressures generated during the initial construction of the foundations. The design problem is determining how large this increase in undrained strength is, since this will determine the amount of new load that can be applied. This paper provides guidelines to answering this question through a numerical study of preloaded surface footings on both soft and stiff clay foundations. Additional information resulting from this study addresses the footing failure mechanisms, as well as the effect of a surface crust in soft clay on both the bearing capacity and the failure mechanism. [ABSTRACT FROM AUTHOR]

Discusses the applicability of shallow foundations in semiempirical methodologies that are based on linear and nonlinear models of behavior. Tests on shallow circular foundations; Footing settlement evaluation using cone penetration tests; Conclusions about application of the method to residual materials; Settlement evaluation by adaptation of Wahls and Gupita method using triaxial test results alone.

A fully instrumented experiment was conducted to investigate the soil-structure interaction of single short, stiff laterally loaded piles. A hollow steel pipe pile with a diameter of 102 mm, a thickness of 6.4 mm, and a length of 1.524 m was installed in well-graded sand and subjected to increasing lateral load. The pile and surrounding soil were fully instrumented using advanced sensors, including flexible shape acceleration arrays, thin tactile pressure sheets, and in-soil null pressure sensors. The sensors attached to the pile were used to develop the compressive soil-pile interaction pressures and the lateral displacement along the pile length. The tactile pressure sheet sensors provided the soil-pile interaction compressive pressures on the circumference of the pile at a specific depth and along the length of the pile. The measured soil-pile interaction compressive pressures combined with the measured lateral displacement along the pile length were used to develop the soil-pile interaction force-displacement relationships ( curves) using direct measurements. In addition, the in-soil null pressure sensor measurements were used to develop the distribution of horizontal stress changes around the pile as the lateral pile displacement increased. When appropriate, the measured results were compared with data and methods available in the literature. [ABSTRACT FROM AUTHOR]