Bearing Capacity Theory Research Articles

Discussion of “Bearing Capacity Theory from Experimental Results”

Discussion of “Bearing Capacity Theory from Experimental Results”

Discussion of “Bearing Capacity Theory from Experimental Results”

Discussion of “Bearing Capacity Theory from Experimental Results”

The Behavior of Piles Driven in Clay. II. Investigation of the Bearing Capacity Using Total and Effective Strength Parameters

This paper outlines research of large model piles and some full scale piles driven into insensitive clay to study the phenomenon of load transfer and the effect of pile driving on the soil. It is divided into two parts. Part I dealt with the stress field set up by driving a large model pile into an instrumented clay bed and the stresses measured for some full scale timber piles. Part II presents an evaluation of the load carrying capacity of the model pile and compares the results with full scale load tests. Soil properties are evaluated in terms of effective stress for an estimate of the bearing capacity of the piles.The short term bearing capacity of the pile shaft and base can be estimated by conventional methods based on the undrained shearing strength of the clay at the time of driving. However, after several load cycles and for long term bearing capacity, closer estimates are obtained by use of the effective skin friction and shearing strength parameters from drained tests. Previous bearing capacity theory can be used for estimating the ultimate base capacity and an approximate theory is presented to estimate the average effective radial stress on the pile shaft in connection with the ultimate shaft capacities. This proposed approach is supported by observations in some clays of low sensitivity, but requires further research in other types of clays.

Boulder tracks and nature of lunar soil

Boulder tracks from 19 different locations on the Moon, observable in Lunar Orbiter photographs, have been examined. Measurements of the track width indicate that some of the boulders sank considerably deeper than others. It is suggested that lunar surface materials vary from place to place; the state of compaction (density of lunar soil) is probably one of the significant variables. Using bearing capacity theory, modified to be applicable to the rolling boulder problem by theoretical studies and extensive testing, the friction angle of the lunar soil was estimated. Most of the results were between 24 and 47 degrees with an arithmetic average of 37 degrees. These values suggest corresponding density variations of 1.25 to 2.00 g/cm3.

Bearing Capacity Theory from Experimental Results

The development of a theory of bearing capacity of strip footings on cohesionless soils, based on a failure surface deduced from the experimentally observed surfaces, is reported in this article. The deduced surface is different from the failure surfaces assumed in the commonly used theories. In the high ranges of the angle of internal friction of soil the deduced surface is much smaller than those assumed in theories. When the plane-strain value of the friction angle of soil is used, the developed theory gives a very accurate prediction of the bearing capacity while the existing theories fail to do so.

Bearing Capacity of Anisotropic Cohesive Soil

A new description of anisotropic cohesive strength provides a simple solution for the bearing capacity of a strip load, based on previous work by Hill. This solution and a survey of published data on anisotropic shear strength indicate that the bearing capacity at worst is 85% of what would be predicted using conventional shear strength data for vertical compression and bearing capacity theory. The bearing capacity is 90% of that predicted by conventional theory and the average of strength from vertical and horizontal compression. When compressive strength is available for three orientations of loading, the shear strength can be represented as an ellipse, and the bearing capacity depends on the shape of the ellipse and on the average of vertical and horizontal compressive strengths.

Elastic-Plastic Foundation Model for Punch-Shear Failure

A new foundation model which has been proposed in the literature, and which consists of two elastic spring layers interconnected by an elastic shear layer, is generalized herein to include the effect of plastic yielding in the foundation on the foundation response. By postulating an elastic-perfectly plastic constitutive relation for the shear layer, one obtains a model which simulates the punch-shear failures observed in highly compressible soils, a phenomenon not covered by the Prandtl type bearing capacity theory. For simplicity, the classical two-dimensional problem of an infinitely long rigid strip resting on the surface of the subgrade is treated. The effect of yielding on the load-deflection curve and contact pressure distribution is discussed. The theoretical results are in qualitative agreement with the limited available experimental data.

Failure of an Oil Storage Tank Founded on a Sensitive Marine Clay

The investigation of the failure of an oil storage tank founded on a sensitive, soft-to-firm clay is described. The history of the failure and the geotechnical properties of the clay are reported. Failure occurred during first loading, and an analysis in terms of total stresses has been carried out. The applicability of bearing capacity theories to foundations on this type of clay has been examined, particularly the propositions that either the bearing capacity factor, or the measured strength of the clay, should be reduced to allow for local shear or progressive failure effects.The results of the analysis indicate that the Skempton-Meyerhof bearing capacity factor for circular loaded areas, Nc = 6.2, may be used, and that the full measured strength of the clay is mobilized.

The basic sinkage equations and bearing capacity theories

THE SINKAGE OF A VEHICLE IS AN IMPORTANT FACTOR IN MOBILITY INVESTIGATIONS, SINCE IT AFFECTS THE MOTION RESISTANCE AND ULTIMATE IMMOBILIZATION OF THE VEHICLE. A DISTINCTION SHOULD BE MADE BETWEEN SETTLEMENTS AND SINKAGE; THE FORMER ARE RELATIVELY SMALL AND PRIMARILY CAUSED BY CONSOLIDATION AND MINOR ELASTIC AND PLASTIC DEFORMATIONS, WHEREAS SINKAGES ARE DUE TO FAILURE AND DISPLACEMENT OF SOIL BELOW THE LOADED AREA AND ARE USUALLY MUCH LARGER THAN SETTLEMENTS. THE FIRST PART OF THIS REPORT CONTAINS A BRIEF REVIEW OF THE FREQUENTLY USED LOAD-SINKAGE RELATION, OR BASIC SINKAGE EQUATION. THE REPORT IS CONCLUDED WITH SOME RECOMMENDATIONS CONCERNING NEEDED BASIC RESEARCH ON SCALE FACTORS IN EXTRAPOLATING RESULTS OF SMALL-SCALE TESTS AND ON THE INFLUENCE OF AN ADDITIONAL TANGENTIAL LOAD OR INCLINATION OF THE TOTAL LOAD. THE GREATEST AREA OF UNCERTAINTY CONCERNS VALUES OF THE INCLINATION FACTORS FOR A LOAD INCLINATION IN DIRECTION OF THE AXIS OF THE CONTACT AREA. FIRST PRIORITY IS SUGGESTED FOR SIMPLE SINKAGE TESTS WITH NORMAL LOADING OF CIRCULAR PLATES AND SYSTEMATIC VARIATION OF THE PLATE DIAMETER. THESE TESTS SHOULD YIELD DATA FOR A MORE ACCURATE DETERMINATION OF THE SCALE FACTORS, WILL FACILITATE DEVELOPMENT OF IMPROVED FORMS OF THE SINKAGE EQUATIONS, OR WILL INDICATE THE MINIMUM VALUES OF PLATE WITH SIMPLIFIED FORMS OF THE SINKAGE EQUATIONS. SECOND PRIORITY IS ASSIGNED TO SYSTEMATIC IN SITU TESTS WITH ANNULAR PLATES HAVING RIBS, OR TEETH, OR IMPROVED DESIGN. THE TESTS SHOULD FURNISH INFORMATION ON SINKAGES CAUSED BY EXCEEDING THE BEARING CAPACITY FOR INCLINED LOADING AND SHOULD INDICATE THE LOWER AND UPPER LIMITS OF THE VERTICAL UNIT LOAD FOR WHICH THE PEAK SHEAR STRENGTH CAN BE DETERMINED RELIABLY BY IN SITU PLATE SHEAR TESTS. VALUES OF INCLINATION FACTORS FOR LOAD INCLINATIONS PARALLEL TO THE AXIS OF THE CONTACT AREA CAN ALSO BE ESTIMATED FROM SUCH DATA. /AUTHOR/

The Ultimate Bearing Capacity of Foudations

Synopsis In the first part of the article a theory of bearing capacity is developed, on the basis of plastic theory, by extending the previous analysis for surface footings to shallow and deep foundations in a uniform cohesive material with fntemal friction. The theoretical results are represented by bearing capacity factors in terms of the mechanical properties of the soil, and the physical characteristics of the foundation. The base resistance of foundations in purely cohesive material is found to increase only slightly with foundation depth; for deep foundations the skin friction is, therefore, large compared with the base resistance. In cohesionless material, however, the base resistance increases rapidly with foundation depth and depends to a considerable extent on the earth pressure coefficient on the shaft; for deep foundations the base resistance is the predominant feature and the shin friction is relatively small. In the second part of the article the main results of laboratory and field loading tests on buried and driven foundations are analysed and compared with the theoretical estimates. The observed base resistance of foundations in clay is in good agreement with the estimates; for deep foundations in soft clay the actual base resistance is somewhat less than estimated, on account of local sheer failure, and an empirical compressibility factor is introduced by which the shearing strength is reduced. The skin friction is found to depend largely on the method of installing the foundation. The observed bearing capacity of shallow foundations in sand is in reasonable agreement with the theory; for deep foundations, however, the actual base resistance is considerably less than estimated on account of local shear failure, and anempirical compressibility factor is introduced as before. Since the earth pressure coefficient on the shaft can at present only be deduced from tho shin friction of penetrating tests, it is frequently more convenient to estimate the bearing capacity of deep foundations in cohesionless soil from an extrapolation of the results of cone penetration tests. Dans la première par-tie de l‘article on expose une théorie sur la capacité de portage, basée sur la théorie de la plasticité, par extension de l'analyse préalable des empattements de surface aux fondations faibles et profondes dans une matiére cohésive uniforme avec friction inteme. Les résultats théoriques sont repésentéb par les facteurs de capacité de portage en fonction des propriétés méaniques du sol et des caractériques physiques de la fondation. La réstance de base des fondations dans un sol vraiment cohésif ne s'accrott que faiblement avec la profondeur des fondations; pourles fondations profondes le frottement superflciel est donc grand par comparaison avec la résistance de base. Cependant, dans des matiéres sans cohésion, la résistance de base s'accrott rapidement avec la profondeur de fondation et déend pour une grande mesure du coefficient de pression de la terre sur la souche; pour les fondations profondes la résistance de base est un facteur de premiére importance et le frottement superiiciel n'a que peu d'importance. Dans la deuxième partie de l'article, on peut voir l'analyse des principaux réhats d'essais de charge en laboratoire et sur le terrain, sur fondations enterrées et enfoncées, et la comparaison avec les prévisions thémiques. La résistance de base observée des fondations dans l'argile Concorde bien avec les évaluations; pour les fondations profondes dans l'argile molle, la résistance de base réelle est quelque peu moindre que celle estimée en raison du man ue de résistance locale au-cisaillement, et on introduit un facteur empirique de compressibilité par lequel la résistance au cisaillement est ré;duite. On trouve que le frottement superficiel dépend beaucoup sur la méthode d'installation des fondations. La capacité de portage observée pour les fondations peu profondes dans le sable concorde raisonnablement avec la théorie; pour les fondations profondes, cependant, la résistance de base réelle est bien moindre que celle estimée en raison du manque de résistance locale au cisaillement et un facteur empirique de compressibilité est introduit comme ci-dessus. Comme le coefficient de pression de la terre sur la souche ne peut à l'heure actuelle étre déluit que d'aprés le frottement superficiel des essais de pénétration. il est souvent lus commode d'estimer la capacité de portage des fondations profondes en terrain sans cohésion d'aprés une extrapolation des résultats des essais de pé;né;tration au cône.

THE BEARING CAPACITY OF SCREW PILES AND SCREWCRETE CYLINDERS.

Summary This Paper describes an investigation which included model-experiments and full-scale loading tests on screw piles and cylinders, observations on the settlement of piles in actual structures, the derivation of a theory of bearing capacity, a check on the relationship between the driving torque and the bearing capacity of the pile, and the formulation of design rules. Two important factors, the first of which does not appear to have been appreciated previously, emerge from this investigation: they are that the value of the coefficient of earth-pressure at rest is a critical factor in the bearing capacity of structures founded in a frictional medium, and that the effect of screwing a cylinder with a closed nose into dense sand is to raise the horizontal earth-pressure considerably and so to effect a very large increase in the bearing capacity.

The Bearing Capacity of Screw Piles and Screwcrete Cylinders†

Summary This Paper describes an investigation which included model-experiments and full-scale loading tests on screw piles and cylinders, observations on the settlement of piles in actual structures, the derivation of a theory of bearing capacity, a check on the relationship between the driving torque and the bearing capacity of the pile, and the formulation of design rules. Two important factors, the first of which does not appear to have been appreciated previously, emerge from this investigation: they are that the value of the coefficient of earth-pressure at rest is a critical factor in the bearing capacity of structures founded in a frictional medium, and that the effect of screwing a cylinder with a closed nose into dense sand is to raise the horizontal earth-pressure considerably and so to effect a very large increase in the bearing capacity.