Settlement Of Footings Research Articles

Application of a non-coaxial soil model in shallow foundations

The influence of a non-coaxial model for granular soils on shallow foundation analyses is investigated. The non-coaxial plasticity theory proposed by Rudnicki and Rice (J. Mech. Phys. Solids 1975, 23, 371–394) is integrated into a Drucker–Prager model with both perfect plasticity and strain hardening. This non-coaxial model is numerically implemented into the finite-element program ABAQUS using a substepping scheme with automatic error control. The influence of the non-coaxial model on footing settlement and bearing capacity is investigated under various loading and boundary conditions. Compared with the predictions using conventional coaxial models, the non-coaxial prediction results indicate that the settlement of a footing increases significantly when the non-coaxial component of plastic strain rate is taken into consideration, although ultimate footing bearing capacities are not affected significantly. The non-coaxial model has a different effect on footing settlements under different loading and boundary conditions. In general, the discrepancies between coaxial and non-coaxial predictions increase with increasing rotation of principal stresses of the soil mass beneath a footing. It can be concluded that if the non-coaxial component of plastic strain rate is neglected in shallow foundation problems using the finite-element method, the results tend to be non-conservative when designs are dominated by settlement of footings.

Improving the performance of circular foundations using structural skirts

This paper presents the results of an experimental study on the behaviour of circular foundations with a structural skirt resting on sand. The structural skirts are fixed to the perimeter of the foundations, and can be used for new or existing shallow foundations. The test results indicate that this type of reinforcement increases the bearing capacity of subgrades and modifies the load–displacement behaviour of the footing. Skirt factors are proposed that take into account the variables that affect the bearing capacity, and they are used within the general bearing capacity equation for shallow circular foundations on sand. Also it was found that the structural skirts reduce the settlement of surface footings compared with footings without structural skirts. At a working stress equal to 50% of the ultimate bearing capacity, the settlement of a surface footing can be reduced to just 11% of that for a footing without a structural skirt. Cet exposé présente les résultats d'une étude expérimentale sur le comportement de fondations circulaires ayant une jupe structurale reposant sur le sable. Les jupes structurales sont fixées sur le pourtour des fondations et peuvent être utilisées pour les fondations peu profondes qu'elles soient en cours d'installation ou déjà installées. Les résultats des essais indiquent que ce type de renfort augmente la capacité porteuse des fonds de forme et modifie le comportement de charge-déplacement de l'assise. Nous proposons des facteurs de jupe qui prennent en compte les variables qui affectent la capacité porteuse; ces facteurs sont utilisés dans l'équation générale de capacité porteuse pour les fondations circulaires peu profondes sur le sable. Nous avons également trouvé que les jupes structurales montrent un affaissement des assises en surface inférieur à celui des assises sans jupes structurales. Avec une contrainte de travail égale à 50% de la capacité porteuse ultime, l'affaissement d'une assise de surface représente seulement 11% de celle d'une assiste sans jupe structurale.

An Improved Experimental Test Set-up to Study the Performance of Granular Columns

Abstract This paper describes an innovative design of a newly developed large test setup for testing the performance of footings supported on soft clay reinforced with granular columns. This advanced testing method is used to examine the settlement of footings supported on granular columns. Two important features of the equipment are (a) the axial loading system which allows samples to be consolidated under Ko condition while the load is applied onto a small foundation area of the sample, and (b) a relatively large sample size of 300-mm diameter and 400-mm high. The system is also equipped with pressure cells located beneath the footing and top cap to measure the pressure distribution with respect to foundation displacement and a lateral strain gage to monitor boundary effects. This paper reports on some of the early findings from the preliminary tests carried out using this equipment. Samples for testing were prepared by consolidating kaolin slurry in a large one-dimensional consolidation chamber. The granular columns were installed using the replacement method by compacting crushed basalt (uniformly graded with 90 % between 1.5–2-mm particle sizes) into a preformed hole. The preliminary tests have yielded promising results, validating the functionality of the equipment and support the prospect of increasing the knowledge with respect to settlement response and design of a footing supported on granular columns.

Resistance factors for settlement design

To control serviceability problems arising from excessive settlement of shallow footings, geotechnical design codes generally include specifications regarding maximum settlement, which often govern the footing design. Once the footing has been designed and constructed, the actual settlement it experiences on a real three-dimensional soil mass can be quite different than expected, due to the soil's spatial variability. Because of this generally large variability (compared to other engineering materials, such as concrete and steel) and because this particular serviceability limit state often governs the design, it makes sense to consider a reliability-based approach to settlement design. This paper looks in some detail at a load and resistance factor design (LRFD) approach to limiting footing settlement. In particular, the resistance factors required to achieve a certain level of settlement reliability as a function of soil variability and site investigation intensity are determined analytically using random field theory. Simplified approximate relationships are proposed and tested using simulation via the random finite element method. It is found that the simplified relationships are validated both by theory and simulation and so can be used to augment the calibration of geotechnical LRFD code provisions with respect to shallow foundation settlement. Key words: reliability-based design, settlement, geotechnical, shallow foundation, random field, probability.

Geotechnical Modelling by Professor David Muir Wood (University of Bristol), Spon Press (London & New York), 2004, Applied Geotechnics Volume 1, ISBN 0-415 34306-6 (hbk), £80.00, ISBN 0-419-23730-5 (pbk), £25.00

Professor Muir Wood puts an interesting slant on soil mechanics theory: all theoretical solutions are just models. This proposition allows him to write a book on geotechnical modelling which is populated by many of the simple, classical, solutions that are the stock in trade of the undergraduate (or maybe Masters’) course in soil mechanics. However, the central idea means that some of the solutions that are lumped together are a rather eclectic collection: for example, under ‘empirical models’ we find the vane test, the pressuremeter, cone tests and their correlation with settlement of footings on sand, and Skempton & Bjerrum's slant on consolidation settlement. However, the idea is exhausted by the end of …

Closely Spaced Footings on Geogrid-Reinforced Sand

The results discussed in this paper are based on a total of 74 tests performed on closely spaced strip and square footings on geogrid-reinforced sand. The study was carried out to evaluate the effect of spacing between the footings, size of reinforcement, and continuous and discontinuous reinforcement layers on bearing capacity and tilt of closely spaced footings. The interference effects on bearing capacity and settlement of closely spaced square footings on reinforced sand were almost insignificant in comparison to those on isolated footings on reinforced sand; whereas a significant improvement in the tilt of adjacent square footings has been observed by providing continuous reinforcement layers in the foundation soil under the closely spaced footings. A considerable improvement in bearing capacity, settlement, and tilt of adjacent strip footings has been observed by providing continuous reinforcement layers in the foundation soil under the closely spaced strip footings.

Estimation of Footing Settlement in Sand

The settlement of foundations under working load conditions is an important design consideration. Well‐designed foundations induce stress‐strain states in the soil that are neither in the linear elastic range nor in the range usually associated with perfect plasticity. Thus, in order to accurately predict working settlements, analyses that are more realistic than simple elastic analyses are required. The settlements of footings in sand are often estimated based on the results of in situ tests, particularly the standard penetration test (SPT) and the cone penetration test (CPT). In this article, we analyze the load‐settlement response of vertically loaded footings placed in sands using both the finite element method with a nonlinear stress‐strain model and the conventional elastic approach. Calculations are made for both normally consolidated and heavily overconsolidated sands with various relative densities. For each case, the cone penetration resistance qc is calculated using CONPOINT, a widely tested program that allows computation of qc based on cavity expansion analysis. Based on these analyses, we propose a procedure for the estimation of footing settlement in sands based on CPT results.

Ultimate Bearing Capacity and Settlement of Footings on Reinforced Sandy Ground

The applicability of a method for predicting ‘bearing capacity increase’ in reinforced sandy ground was examined using tests performed under various test conditions. It was found that the present method predicted, with reasonable accuracy, the bearing capacity increase in sandy ground, reinforced with stiff reinforcement. This method may not be applicable for sandy ground reinforced with extensible reinforcement due to the unsuccessful formation of a semi-rigid zone under the footing. An investigation into the settlement of a footing on reinforced sandy ground, at ultimate footing load condition, suggested that the settlement of footing for reaching peak footing load may be correlated to the ‘deep-footing’ and the ‘wide-slab’ mechanisms. That is, the ultimate settlement ratio between reinforced and unreinforced model sandy ground, SR f , may be linearly correlated to ‘BCR D and ‘BCR S ’, which represent ‘deep-footing’ and ‘wide-slab’ effects, respectively, on the ultimate bearing capacity increase in reinforced sandy ground.

Elastic Settlements of Circular Footings on Geosynthetic-Reinforced Soil

The interactions between soil and a buried circular geosynthetic reinforcement layer placed below a circular load are studied using elastic continuum theory with particular regard for the reinforcement effect in reducing surface settlements. To represent the displacement at the soil-inextensible geosynthetic reinforcement interface, the net radial displacements are equated to zero, and for the soil-extensible geosynthetic reinforcement interface, the net radial displacements are equated to the radial elongations assuming the reinforcement behaves as a thin membrane. A parametric study illustrates the effect of the reinforcement layer radius and depth on reducing surface settlements.

Deformation zones under square footings supported by clayey soils

Footing settlements depend not only on physical and mechanical properties of base soils, but also on applied load intensities and their distributions with depth, as well as on footing rigidity, shape and dimensions. An analytical expression relating rigid bearing plate and/or footing settlements to thicknesses of deformation (active) zones, which form below footing bottoms, has been previously offered by the author. The results of tests performed with 0.5, 1.0 and 4.0 m 2-area square footings, constructed on undisturbed clayey soils and containing data describing active zone development, were collected from literature and analyzed. This paper presents graphical relationships between square footing settlements, active zone thicknesses and footing dimensions, which are verified by published test results performed with experimental square footings, having areas different than the ones selected for statistical analyses.

Elastic settlement and rotation of rectangular footings on nonhomogeneous soil

Keywords: Elasticity ; footings ; foundations ; numerical modelling and analysis ; settlement ; soil ; structure interaction ; stiffness ... Show All

Down-Hole Collapse Test System

An in-situ collapse test for collapsible soils was developed. The test is conducted in a borehole with a load applied to a loading plate at the base of the hole. Water is introduced, and the load-displacement response of the soil is monitored. An analysis of the stress and the degree of wetting encountered during this test was based on a combination of field investigation (empirical data) and finite-element analyses. These studies enabled the development of a technique by which the load-displacement data, obtained from the test, can be converted to stress-strain data. Simplified charts for interpretation of the in-situ test results are presented. A series of in-situ collapse tests was performed at a site known to exhibit wetting-induced collapse. A footing test, in which collapse settlements were induced, was also performed at this site. The recommended analysis of the in-situ test was used, and close agreement was obtained between estimated footing settlement and observed settlement.

Liquefaction during the 1977 San Juan Province, Argentina earthquake ( M s = 7.4 )

Liquefaction effects generated by the 1977 San Juan Province, Argentina, earthquake ( M s = 7.4 ) are described. The larger and more abundant effects were concentrated in the 60-km long band of the lowlands in the Valle del Bermejo and in an equally long band along the Rio San Juan in the Valle de Tulum. Fissures in the Valle del Bermejo were up to several hundred meters long and up to several meters wide. Sand deposits, from boils that erupted through the fissures, covered areas up to tens of square meters. Fissures generally parallelled nearby stream channels. Because the Valle del Bermejo is undeveloped, these large features caused no damage. Liquefaction in the Valle del Tulum caused important or unusual damage at several localities, including the following five sites: (1) At the Barrio Justo P. Castro, a subdivision of Caucete, liquefaction of subsurface sediments decoupled overlying, unliquefied stiff sediments, producing a form of ground failure called “ground oscillation”. The associated differential ground movements pulled apart houses and pavements in extension, while shearing curbs and buckling canal linings in compression at the same locality. (2) At the Escuela Normal, in Caucete, the roof of a 30-m long single-story classroom building shifted westward relative to the foundation. That displacement fractured and tilted columns supporting the roof. The foundation was fractured at several places, leaving open cracks, as wide as 15 mm. The cumulative width of the open cracks was 48 mm, an amount roughly equivalent to the 63 mm of offset between the roof and foundation at the east end of the building. The ground and foundation beneath the building extended (or spread) laterally opening cracks and lengthening the foundation while the roof remained in place. (3) The most spectacular damage to structures at the community of San Martin was the tilting of a 6-m high water tower and the toppling of a nearby pump house into a 1-m deep crater. Similarly, a small crater developed beneath a hand-pump in an open area and a large, 6-m diameter crater formed nearby. The following sequence of events created the craters and toppled the pump structures: During the earthquake, ground shaking generated excess pore pressures which were dissipated by upward flow of groundwater. Free drainage was restricted by an impermeable plastic-silt layer. Water apparently accumulated below the plastic-silt layer and then burst to the surface through several holes and cracks, including holes around well casings. (4) At the San Isidro winery, nine storage tanks tilted 2 to 5°. Five reinforced-concrete tanks were dismantled but four steel tanks were repaired by placing new footings and jacking the structures into an upright position. (5) At Escuela J.J. Pasos, differential settlement beneath building fractured several columns and walls. The largest settlements were about 60 mm and the maximum settlement of footings supporting columns was about 40 mm. In spite of the damage, the buildings were in no danger of collapse.

Settlement and rotation of footings embedded in sand. Technical note: Georgiadis, M Soils FoundV33, N1, March 1993, P169–175

Settlement and rotation of footings embedded in sand. Technical note: Georgiadis, M Soils FoundV33, N1, March 1993, P169–175

Settlement and Rotation of Footings Embedded in Sand

A series of model tests has been conducted to study the effect of footing embedment and load eccentricity on the load-settlement and moment-rotation relationships as well as on the bearing capacity. A method was developed for predicting the nonlinear response of an embedded footing, which uses elasticity theory to model soil behavior at low load levels and then incorporates soil nonlinearity in compliance with the experimental behavior. In addition, the effect of embedment on the interaction diagrams between vertical loads and moments that cause failure of the footing is analyzed.

Probabilistic evaluation of settlements of spread footings on sand : Greco, V R Proc 2nd International Conference on Foundations and Tunnels, London, 19–21 September 1989V1, P83–88. Publ Edinburgh: Engineering Technics Press, 1989

Probabilistic evaluation of settlements of spread footings on sand : Greco, V R Proc 2nd International Conference on Foundations and Tunnels, London, 19–21 September 1989V1, P83–88. Publ Edinburgh: Engineering Technics Press, 1989

Settlement of footings on sandy soil under vertical vibratory loadings : Proc Ninth Southeast Asian Geotechnical Conference, Bangkok, 7–11 December 1987 V2, P7.1–7.12. Publ Bangkok: Southeast Asian Geotechnical Society, 1987

Settlement of footings on sandy soil under vertical vibratory loadings : Proc Ninth Southeast Asian Geotechnical Conference, Bangkok, 7–11 December 1987 V2, P7.1–7.12. Publ Bangkok: Southeast Asian Geotechnical Society, 1987

Prediction of settlement of shallow footings on sand: some observations: Giddings, T R Proc Int Conference on Foundations and Tunnels, London, 24–26 March 1987V1, P20–24. Publ Edinburgh: Engineering Technics Press, 1987

Prediction of settlement of shallow footings on sand: some observations: Giddings, T R Proc Int Conference on Foundations and Tunnels, London, 24–26 March 1987V1, P20–24. Publ Edinburgh: Engineering Technics Press, 1987

Settlement of Shallow Foundations on Granular Soils

A conceptual framework for understanding the effects of overconsolidation in reducing the compressibility of all types of soils is presented. A generally applicable method for estimating the settlement of footings on granular soils is presented. The procedure uses a combination of dilatometer and cone-penetration test results to identify the preconsolidation pressure, while soil moduli—either Young’s modulus or constrained modulus, depending on the boundary conditions—are obtained from the dilatometer test results. Calibration chamber test results are used to adjust the dilatometer moduli for the effects of stress path and for disturbance due to insertion of the instrument. Detailed examples are given to illustrate the use of the method and to compare the results obtained with those calculated using currently accepted methods for estimating settlements.

Procedures for predicting settlements in sands : Jeyapalan, J K; Boehm, R In: Settlement of Shallow Foundations on Cohesionless Soils: Design and Performance (papers to the ASCE Convention, Seattle, 10 April 1986)P1–22 Publ New York: ASCE, 1986 (Geotechnical Special Publication No 5)

In many cases, the prediction of settlements of footings on sands involves use of empirical rules. Although many approaches are reported in the literature, the relative accuracy of these methods for settlement predictions has not been evaluated in detail. In this paper, nine of such procedures are reviewed and then applied in 71 case histories. Each of these prediction methods is statistically analyzed, based upon a comparison of the predicted and observed settlements.