Triaxial Strength Research Articles

Effect of Stress Concentrations on the Cyclic Behavior of Sands

Abstract A laboratory study is presented on the effect of rigid inclusions on the observed cyclic strength of sand specimens. The test program consisted of 20 cyclic triaxial strength tests. Sixteen of these tests were conducted on specimens that had a spherical cemented sand inclusion of varying diameter located in either the middle or upper third of the specimen. The remaining four specimens were homogeneous. Results indicated that the cyclic strength of a specimen with an inclusion was increased up to a maximum of 6 to 7% over that of a corresponding homogeneous specimen at an area ratio (area of inclusion/area of specimen) of 10%. An increase in the area ratio to 25% showed a decrease in cyclic strength to a level similar to that exhibited by a homogeneous specimen. In addition, for a constant area ratio the increase in cyclic strength was shown to be greatest for a low stress ratio.

Normalized Dynamic Undrained Strength of Sands Subjected to Cyclic and Random Loading

Normalized cyclic undrained triaxial stress-strain relationships of undisturbed sandy specimens are discussed in this paper. Cyclic undrained triaxial strengths defined by axial strain amplitudes and developments of excess pore water pressure are analyzed. A simplified equation for evaluating cyclic undrained triaxial strength of sands is derived. Based on the empirical normalized strength equation, a relationship between strength for a uniform cyclic loading and that for a random cyclic loading is obtained. A simplified method for evaluating an equivalent uniform loading strength for a random loading is proposed using a strength curve through uniform cyclic loading tests.

Estimating the triaxial strength of rocks. Technical note : Brook, N Int J Rock Mech Min Sci, V16, N4, Aug 1979, P261–264

Estimating the triaxial strength of rocks. Technical note : Brook, N Int J Rock Mech Min Sci, V16, N4, Aug 1979, P261–264

A mathematical description of the strength properties of concrete under generalized stress

Synopsis A mathematical description of the ultimate strength envelope of concrete under axisymmetric stress states has been derived by analysing experimental data obtained in previous investigations of the Concrete Materials Research Group at Imperial College. The derived equations, when combined with an proposed elsewhere for the description of the effect of the intermediate stress σ2 upon the ultimate strength level, define a surface in stress space which provides a simple mathematical representation of the ultimate strength of concrete under generalized short-term loading conditions. The resulting ultimate strength surface conforms with generally accepted shape requirements and has been found to provide a close fit for most biaxial and triaxial strength data published to date.

End restraint effects on cyclic triaxial strength of sand : Lee, K L; Vernese, F J J Geotech Engng Div, ASCE, V104, NGT6, June 1978, P705–719

End restraint effects on cyclic triaxial strength of sand : Lee, K L; Vernese, F J J Geotech Engng Div, ASCE, V104, NGT6, June 1978, P705–719

End restraint effects on undrained static triaxial strength of sand : Lee, K L J Geotech Engng Div, ASCE, V104, NGT6, June 1978, P687–704

End restraint effects on undrained static triaxial strength of sand : Lee, K L J Geotech Engng Div, ASCE, V104, NGT6, June 1978, P687–704

End Restraint Effects on Cyclic Triaxial Strength of Sand

Cyclic triaxial tests were performed on various soils at different densities and different consolidation pressures, using regular and lubricated ends to explore the possible effect of end restraint...

End Restraint Effects on Undrained Static Triaxial Strength of Sand

Although many studies have been made on the effect of end restraint in triaxial testing of soils, no data were available pertaining to static undrained tests on saturated sands. Therefore, a series of tests were conducted using triaxial specimens with regular and frictionless ends. The results showed that for a medium dense sand there was a significant (up to 20%) increase in static undrained strength with frictionless ends as compared with tests using regular ends. The effect is significantly greater than observed for other studies pertaining to drained tests on sands and undrained tests on clays. The strong effect in this case was shown to be related to the difference in volume change/pore pressure change tendencies between tests with regular and frictionless ends as measured by the critical confining pressure. The study was undertaken as a prelude to a similar companion study on the influence of end restraint in undrained cyclic tests on saturated sand.

Specimen Preparation and Cyclic Stability of Sands

The results of a study on the cyclic structural stability of saturated sands as determined by the cyclic triaxial strength test (liquefaction test) are presented. The results clearly demonstrate that the method of specimen preparation can significantly affect the cyclic behavior of sands, and this effect is most likely directly related to variances in the fabric of the sand. It is also concluded that a better understanding of the strain development characteristics of sands could play an important role in evaluating the results of cyclic triaxial strength tests.

Discussion of “Cyclic Triaxial Strength of Standard Test Sand”

Discussion of “Cyclic Triaxial Strength of Standard Test Sand”

Erratum for “Cyclic Triaxial Strength of Standard Test Sand”

Erratum for “Cyclic Triaxial Strength of Standard Test Sand”

Cyclic triaxial strength of standard test sand : Silver, ML Univ. Illinois, Chicago, USA Chan, CK Ladd, RS Woodward-Llyde, Clifton, NJ, USA 10F, 2T, 5R. J. Geotech. Engng Div. ASCE, V102, GT5, 1976, P511–523

Cyclic triaxial strength of standard test sand : Silver, ML Univ. Illinois, Chicago, USA Chan, CK Ladd, RS Woodward-Llyde, Clifton, NJ, USA 10F, 2T, 5R. J. Geotech. Engng Div. ASCE, V102, GT5, 1976, P511–523

Cyclic Triaxial Strength of Standard Test Sand

A cooperative cyclic triaxial strength test program was performed by eight university, government, and consulting laboratories to define the cyclic strength characteristics often called the liquefaction potential or cyclic mobility of a standard test sand. Other laboratories may check the adequacy of their cyclic triaxial test equipment and testing procedures by duplicating the results of these tests. It was found that a good degree of agreement for cyclic soil strength values could only be achieved among different laboratories when proper attention was given to the following testing details: (1) Great care must be taken in measuring specimen dimensions and weight to accurately calculate specimen dry weight; (2) tested specimen dry weights must be within 0.5 pcf (8 kg/m²) of the specified value; (3) specimen preparation techniques must not deviate from the specified method; and (4) a smooth periodic loading wave form, such as a sine wave, should be used for testing.

Triaxial strength of rock materials

Triaxial Strength of Rock Materials An attempt is made to define the nature and purposes of triaxial strength criteria, also to outline some factors to be considered in their selection and use. Seven alternative empirical strength criteria are compared on the basis of their simplicity and their fit to data for some fifteen hundred rock and concrete specimens. Two of these, one linear and one curved, are then compared in detail. Use of the curved rather than the linear criterion resulted in a significant reduction in strength prediction error. Methods of fitting the criteria to strength data are described. The parameters of the two criteria are then used to compare and classify rocks on the basis of their triaxial strength behaviour. Possible alternative formulations of the two criteria are considered in an appendix.

Developments in triaxial testing technique

A simple triaxial cell is described together with details of the technique employed for triaxial testing. Triaxial strength results for 254 specimens of eight rock types are tabulated.

Stability of Sand Arches: A Key to Sand Control

Sand production, from a well completed in an incompetent formation without a metal screen, can be attributed to failure of the sand to form a stable arch around the wellbore or over a perforation. This study shows the usefulness of having a sand of high grain strength outside the perforations, and indicates that even a low-strength plastic can provide the restraint necessary to stabilize an arch. Introduction The petroleum industry has used both mechanical and chemical methods for controlling the production of sand from wells completed in unconsolidated formations. In developing sand control methods, mechanical studies have dealt mostly with the design of screens and slotted liners and the placement of gravel packs; chemical studies have dealt with the composition and performance of sand consolidation plastic systems, and techniques of applying them. Little attention has been paid in the literature to the mechanical process of failure of the sand structure around a wellbore and the factors that affect the stability of the formation. Our laboratory has conducted, in the past several years, both theoretical and experimental studies on the mechanics of sand failure. W.M. Ayers,1 in 1965, presented results of his theoretical studies combined with field experience. He discussed the stress field around a wellbore and its relation to the formation stability in terms of the shear strength properties of the sand. The work being reported here was a laboratory extension of Ayers' studies. It was conducted as a basic study of sand control and was carried out. in two phases:elucidation of the failure mechanisms of unconsolidated sands and of the mechanism of stabilization of sands by consolidating plastics, using triaxial strength tests; anda direct study of the arching behavior of sand, or the manner in which sand can form a stable structure spanning an opening. Background Shear Strength of Sand The study of the strength of bodies of granular materials generally falls within the realm of soil mechanics. A widely used criterion for shear failure of soils is the Mohr-Coulomb theory.2 This states that failure will occur when the major and minor principal stresses s1 and s3 combine to produce a critical and characteristic value of the obliquity, which is the ratio of shear stress t to normal stress s in the plane of shearing. The validity of this criterion, which ignores the intermediate principal stress s2, is supported by experimental evidence cited by Bishop.3 The shear strength of a sand may therefore be described in terms of a Mohr envelope and its slope a, the angle of shearing resistance. Shear Strength of Sand The study of the strength of bodies of granular materials generally falls within the realm of soil mechanics. A widely used criterion for shear failure of soils is the Mohr-Coulomb theory.2 This states that failure will occur when the major and minor principal stresses s1 and s3 combine to produce a critical and characteristic value of the obliquity, which is the ratio of shear stress t to normal stress s in the plane of shearing. The validity of this criterion, which ignores the intermediate principal stress s2, is supported by experimental evidence cited by Bishop.3 The shear strength of a sand may therefore be described in terms of a Mohr envelope and its slope a, the angle of shearing resistance.

The Mechanical Properties of an Interlocked Low-Porosity Aggregate

Synopsis If coarse grained marble is heated to around 6OO°C the anisotropy of thermal expansion of calcite causes almost complete separation at grain boundaries. The resulting material retains its shape and consists of a mass of crystals in contact, with a porosity of about 4%, very small direct tensile strength and the mechanical analysis and permeability to water of a sand. It may be regarded as a laboratory model of randomly jointed rock and perhaps of bad and broken rock in general. It has frequently been suggested that soil mechanics theory may be applied to such rock. This Paper examines the mechanical properties of the heated marble and shows that they different from those of soils. A small amount of confining pressure varies the triaxial strength rapidly, the initial slope of the Mohr envelope being of the order of 65° and the strength finally increasing to over 80% of that of the original rock. Young's modulus also increases with confining pressure but only to about 30% of that of original rock. Even if one principal stress is tensile, a perpendicular compressive stress greatly increases the strength. Model ‘plate bearing’ tests give the same value of Young's modulus as compression of cylinders, suggesting that this may be true for full scale tests on bad rock. Permeability is found to decrease rapidly with confining pressure and slightly with uniaxial stress. Pronounced effects of size on strength are observed which appear to deviate from the usual power or Protodyakonov laws at small sizes. Si du marbre à grains grossiers est chauffè á environ 600°C l'anisotropie de la dilatation thermique de la calcite provoque une séparation presque complète à la limite de composition des grains. La matière qui en résulte conserve sa forme et est formée d'une masse de cristaux en contact, d'une porosité d'environ 4%, d'une très petite résistance directe à la traction et possédant les qualités d'analyse mécanique et de perméabilité à l'eau d'un sable. On peut la considérer comme un exemple de laboratoire d'une roche assemblée au hasard et peut-être d'une roche de mauvaise qualité et brisée d'une façon générale. Il a été fréquemment suggéré que la théorie de la mécanique du sol pourrait peut-être être appliquée á une telle roche. Cet exposé examine les propriétés mécaniques du marbre chauffté et montre qu'elles sont différentes de celles des sols. Une petite quantité de pression dans une enceinte rigide fait rapidement varier la résistance triaxiale, la pente initiale de la courbe intrinsèque étant de l'ordre de 65° et la résistance augmentant jusqu'à plus de 80% de celle de la roche d'origine. Le module d'Young augmente aussi avec une pression dans une enceinte rigide mais seulement jusqu'à une valeur d'environ 30% de celle de la roche d'origine. Même si une contrainte principale est à la traction, une contrainte de compression perpendiculaire augmente beaucoup la résistance. Des essais de ‘charge sur plaque’ sur maquette donnent la même valeur que le module d'Young qu'une compression de cylindres, suggérant que ceci pourrait étre vrai pour des essais in situ sur des roches de mauvaise qualité On trouve que la perméabilité diminue rapidement avec la pression dans une enceinte rigide, et légèrement avec une contrainte selon un axe. On observe des effets prononcés de la taille sur la résistance qui paraissent ne pas se conformer aux lois de puissance habituelles ou de Protodyakonov pour les petites tailles.

Strength of rock-like materials

This paper deals with the strength of rock-like materials under triaxial stress conditions. The most common theories of brittle fracture are reviewed. Some methods of triaxial strength determination are described and the results compared. The strength dependence of lateral pressure, pore pressure and size of the test sample is described. Some standard tests are suggested. A method for determining the shear strength at high normal pressure has been used as a measure of the strength of a number of Swedish rocks and ores.

Polymer molecular structure and mechanical properties

Abstract The theoretical problem of relating the mechanical properties of a polymer to molecular structure is considered for the simplest case where an amorphous polymer is subjected to a hydrodynamic stress system at high rates of deformation. The theoretical basis is that under such conditions the mechanical properties can be attributed to the London forces between nearest atoms on neighbouring chain molecules. For the amorphous polymers polymethylmethacrylate and polystyrene the calculations give room temperature values of maximum bulk modulus, triaxial and uniaxial brittle fracture strengths and probable brittle fracture strain. Theoretical values of bulk modulus are also obtained for polyethy-lenes of various degrees of crystallinity by considering strain in the amorphous regions only. It is indicated how time dependent or viscoelastic effects might be introduced into the analysis to describe mechanical properties at much lower rates of deformation.