Triaxial Strain Research Articles

The relation between microfabric and strain in a progressively deformed quartzite sequence from Central Australia

In the Ormiston Nappe Complex, west of Alice Springs, central Australia, a deformed zone up to 0.7 km thick is developed in the sedimentary Heavitree Quartzite. The deformed zone is adjacent to a major thrust fault and is defined by mylonitic foliation, which is parallel to the thrust plane and by isoclinal folds. Recognition of original detrital quartz grains allows strain ellipsoids to be measured across the zone. The strain generally plots in the flattening field and many specimens show pure flattening strain. The mylonitic foliation is an axial-plane structure to the folds and is parallel to the XY-plane of the strain ellipsoid. A quartz elongation lineation may be present within the foliation and is parallel to the principal extension direction (the X- axis ) of the strain ellipsoid. Strain is accommodated principally by intracrystalline plastic deformation of the quartz grains. In detail the strain is not homogeneous and may vary even between adjacent grains of the same specimen. Quartz optic axis fabrics reflect this strain inhomogeneity. If the strain ellipsoid is an oblate spheroid, c- axes lie in small-circle girdles about the principal shortening axis (the Z- axis ). With general triaxial strain, the c- axes lie in a great-circle girdle or girdles which intersect the foliation parallel to the intermediate strain axis (the Y- axis ) and lie symmetrically about the Z- axis . A random population of grains from a specimen often shows a composite c-axis pattern between these two types. With approach to the thrust there is an increase in the amount of strain within the specimens. The increasing strain correlates with an increase in the degree of c- axis preferred orientation of the deformed detrital grains and in the amount of new strain-free grains present in the deformed quartzite. Adjacent to the thrust the quartzite is completely composed of polygonal new grains. The new grains probably formed under syntectonic conditions caused by movement along the thrust. The bulk of the new grains developed by increasing misorientation between the subareas of an initially polygonized old grain. There is no evidence of any marked host control on new-grain orientation, but new grain c- axis plots are generally similar to the corresponding old-grain plots from the same specimen.

Triaxial constant strain rate tests and triaxial creep tests on frozen Ottawa sand : Sayles, FH Report. 12R US Army C.R.R.E.L. Report AD 785 506, TR. 253, Aug. 1974, 28P

Triaxial constant strain rate tests and triaxial creep tests on frozen Ottawa sand : Sayles, FH Report. 12R US Army C.R.R.E.L. Report AD 785 506, TR. 253, Aug. 1974, 28P

Triaxial and plane strain creep rupture of an undisturbed clay : Campanella, RG Univ. British Columbia. Vancouver, CDN Vaid, YP Univ. British Columbia. Vancouver, CDN 10F, 25R Can. Geotech. J. V11, N1, Feb. 1974, P1–10

Triaxial and plane strain creep rupture of an undisturbed clay : Campanella, RG Univ. British Columbia. Vancouver, CDN Vaid, YP Univ. British Columbia. Vancouver, CDN 10F, 25R Can. Geotech. J. V11, N1, Feb. 1974, P1–10

Comparative behaviour of an undisturbed clay under triaxial and plane strain conditions : Vaid, YP Thesis. Figs, Tabls, Refs. Univ. British Columbia, CDN, 1971

Comparative behaviour of an undisturbed clay under triaxial and plane strain conditions : Vaid, YP Thesis. Figs, Tabls, Refs. Univ. British Columbia, CDN, 1971

Triaxial and plane strain behaviour of natural clay : 14F, 2T, 15R. J. GEOTECH. ENGNG. DIV. V100, N.GT3, MAR. 1974, P207–224

Triaxial and plane strain behaviour of natural clay : 14F, 2T, 15R. J. GEOTECH. ENGNG. DIV. V100, N.GT3, MAR. 1974, P207–224

Ground stress determinations in Canada

Ground Stress Determinations in Canada Stress determinations with the biaxial (Doorstopper) and the triaxial strain cell of the C. S. I. R., South Africa, are discussed and show that the triaxial cell is the more desirable instrument if good rock conditions exist. Vertical and average horizontal stresses in Canada are similar in magnitude to those from other parts of the earth's crust and show that vertical stresses are related to weight of overburden and average horizontal stresses increase in most of the cases with 0.407 kg/cm2 per metre of depth. More data are necessary to make any prediction for the average horizontal stress beyond a depth of 800 m. Stress determinations and a tectonic analysis show that the unravelling of the geological stress-strain history allows some prediction of principal stress directions, but the attached uncertainties due to gaps in documentation require proof by stress determinations.

Triaxial and Plane Strain Behavior of Natural Clay

Specimens of a saturated, undisturbed marine clay were K 0 consolidated and subsequently sheared under triaxial and plane strain conditions using a variety of stress paths and drainage conditions. It was found that both the undrained strength and the angle of shearing resistance were slightly larger in plane strain than under the corresponding triaxial conditions. Methods to estimate strains in undrained plane strain shear from the results of triaxial tests under identical stress paths have been developed. An extended form of Rendulic's hypothesis was used successfully to predict volumetric strains under plane strain conditions using undrained triaxial results.

Triaxial and Plane Strain Creep Rupture of an Undisturbed Clay

A comparative study of the undrained creep rupture characteristics of a saturated, normally consolidated, undisturbed marine clay has been carried out under triaxial and plane strain conditions. Creep rupture tests were performed on samples which were consolidated both isotropically and under K0 conditions to the same vertical effective stress. It is shown that for a given minimum creep rate or creep stress, large differences in rupture life are observed between conventional isotropically consolidated triaxial samples and K0 consolidated triaxial or plane strain samples. Similar discrepancies are introduced when conventional triaxial results are used to estimate remaining rupture life during tertiary creep stage when the real situation corresponds to either K0 consolidation or plane strain. Effective stress failure in creep rupture for a given type of test is governed by the same linear failure envelope which is obtained during constant rate of shear testing.

First experiences with the C.S.I.R. triaxial strain cell for stress determinations.-Laboratory and field testing procedures and results and computer program for analysis of data obtained : Hergert, G Mines Br. Dept. En. Min. Res. Ontario, CDN 7F, 2T, 7R. Int. J. Rock Mech. Min. Sci. V10, N6, 1973, P599-522

First experiences with the C.S.I.R. triaxial strain cell for stress determinations.-Laboratory and field testing procedures and results and computer program for analysis of data obtained : Hergert, G Mines Br. Dept. En. Min. Res. Ontario, CDN 7F, 2T, 7R. Int. J. Rock Mech. Min. Sci. V10, N6, 1973, P599-522

First experiences with the C.S.I.R. triaxial strain cell for stress determinations

The C.S.I.R. triaxial strain cell allows determination of the three-dimensional stress field in one drill hole. This instrument was tested in the laboratory and in the field to develop testing techniques and to discover areas of possible pitfalls. Compared with the biaxial of stress determination the triaxial method is more efficient and theoretically more desirable to use, however it requires better ground conditions. The waterproofing of electrical contacts and the cleanliness required for strain gauge work underground is an area which requires experience. Some field tests indicate a low stress level parallel to the drill hole which was initially attributed to the particular drill-hole geometry used during the tests. A finite element analysis showed however that for an average rock type the stress component parallel to the drill hole at the point of measurement was reduced by only 3 per cent. During the three field tests, all the overcored cylinders cracked in the vicinity of the strain cell. The existence of a crack across the drill hole prior to overcoring offers an explanation for the low level of measured stress parallel to the drill hole. To check how well the instrument measures strains in three dimensions, a column of aluminium blocks 36 in. high was loaded in uniaxial compression. The strains measured with the triaxial strain cell indicated good agreement (within 5 per cent) between applied and calculated stresses. To facilitate potential use of the equipment and analysis of the data a computer program calculating the tensor of best fit and the error of the tensor components was written and is given in the Appendix.

Behavior of an Archean Granitic Batholith: Discussion

In recent years, the term train' has become increasingly important in descriptive structural geology. Expressions like train facies' or 'strain fabric' (formerly Veformation fabric') have been introduced (Halasen 197 1, Clifford 1972), which are exclusively related to tectonic flow, and these are used with increasing frequency, while use of the term strain is comparatively uncommon in papers on non-diastrophic deformation or flow of lava and magma. If this trend' continues 'geologic strain' will become synonymous with 'tectonic flow'. It need hardly be pointed out that strain is not a structural property but rather a general concept of theoretical mechanics, and that it is not the only method of specifying a coptinuous deforn~ation (minus translation) It has become clear, however, that the strain concept, rather than alternative methods, will be an important tool for the modcrn structural geologist (cf. Ramsay 1969). Clifford's ( 1972) study is essentially an application of the strain theory to the wall rock deformation of a granitic batholith. The paper employs such engineering terms as 'pure shear' and 'simple shear', as well as tectonic expressions related to strain. These technical terms have been unequivocally defined in standard books of theoretical mechanics, and/or in recent textbooks of structural geology (Table 1 ). Clifford ( 1972) does not use 'pure shear' and other expressions in their standard sense, neither does he re-define his technical vocabulary. The reader is forced to deduce from the general context which meaning is to be attached to the various terms (Table 1 ). Clifford ( 1972) prescnts convincing evidence that the triaxial strain of the wall rocks is markedly heterogeneous, i.e. that the magnitude of horizontal compressive strain increases toward the contact of the batholith. Me then claims that this inhomogcneous deformation corresponds closely to irrotational strain (labelled 'pure shear in three dimensions', see Table I ) , and attributes it largely to axially symmetric inflakion of thc uiaconsolidatcd batholith. Of gcomctric necessity, most heterogeneous strains involve large components of rigid rotation, i.e. the local strain is generally rotational (Ramsay 1969, p. 52) . Figure 1 illustrates schematically what heterogencous strains might be expected around uniformly expanding circular diapirs. The cross-sectional strain (normal to the axis of diapirs) must be irrotational (Fig. la ) , but large components of rigid rotation occur in other sections (Fig. l b ) . These components will tend to be greatest where geometry of the granite contact is approximately cylindrical. Inflation of noncircular diapirs will generally lead to rotational crosssectional strain in the sul-rounding rocks. Clifford ( B 972) considers two general models of radial horizontal compression of the supracrustal wall rocks, ( 1 ) by emplacement of a conical granitic mass, and (2) by late-stage horizontal inflation' of a batholith. He asserts that the former model is characterized by biaxial strains (labelled 'constrictive', Table 1 ), and that the latter model involves an early phase of subvertical simple shear parallel to the contact. Figure 1 b illustrates that subverti-

Crash-A Computer Program for the Evaluation of the Creep and Plastic Behavior of Fuel-Pin Sheaths

The computer program CRASH allows the calculation of triaxial stress and strain states in the sheath of cylindrical fuel elements when creep or plasticity occur in the cladding material. Any creep ...

Comparison of Plane Strain and Triaxial Tests on Sand

Conventional laboratory practice consistently uses triaxial test procedures for soil strength investigations although many field cases in soil mechanics approximate plane strain conditions. Data from a wide variety of sources indicate that, for drained tests on sand, plane strain gives the greatest strength. Very little is known about the comparative strength and deformation properties in undrained tests. This study describes a series of drained and undrained tests on saturated sand under a wide range of density and confining pressure conditions using both triaxial and plane strain loading. It was found that, for undrained conditions, at low pressures triaxial tests gave the greatest strengths, but at high pressures the greatest strengths were determined from plane strain loading. Several arguments were offered to explain this and other observations in the behavior of plane strain versus triaxial tests on saturated sands.

The Relationship Between the Shear Strength of Sands in Triaxial Compression, Plane Strain and Direct Shear

The Relationship Between the Shear Strength of Sands in Triaxial Compression, Plane Strain and Direct Shear

Determination of stress in rock with linear or non-linear elastic characteristics

Determination of Stress in Rock with Linear or Non-Linear Elastic Characteristics A non-linear law of elasticity is proposed in which each principal stress is expressed as the summation of two series, one a function of the dilatory (hydrostatic) or octahedral normal strain and the other of the deviatory or octahedral shear strain. The constants in the series can be obtained from a simple uniaxial compression or tension test on the material. These expressions can be used to determine the stress from strain readings in rock having non-linear stress-strain characteristics and the application of these expressions when using the CSIR triaxial strain cell in such rock is demonstrated.

Discussion of “Volume Changes in Triaxial and Plane Strain Tests”

INTERESTING EXPERIMENTAL RESULTS WERE SHOWN BY THE AUTHORS CONCERNING THE DIFFERENCE IN VOLUME CHANGES DURING DRAINED SHEAR OF SAND UNDER TRIAXIAL AND PLANE STRAIN CONDITIONS, RESPECTIVELY. HOWEVER, IN ORDER TO FIND EXPERIMENTALLY THE ACTUAL MAGNITUDE OF THE DIFFERENCE UNDER COMPARABLE CONDITIONS, IT MAY BE NECESSARY TO EXCLUDE FROM THE TESTS THOSE EFFECTS WHICH HAVE NO DIRECT BEARING ON THE INVESTIGATED PROBLEM. THE AUTHORS' QUANTITATIVE COMPARISON OF VOLUME CHANGES OF MOL SAND IN THE TWO TYPES OF TESTS WAS BASED EXCLUSIVELY ON THE RESULTS OF CONVENTIONAL CONSTANT CELL PRESSURE TESTS. HOWEVER, OBSERVED DIFFERENCES MAY BE EXPECTED TO REFLECT THE EFFECT OF DIFFERENT COMPRESSION STRAINS DUE TO DIFFERENT INCREASES IN THE OCTAHEDRAL NORMAL STRESS DURING SHEAR IN BOTH TYPES OF TESTS. IF A TRIAXIAL AND A PLANE STRAIN TEST BOTH START FROM THE SAME CONSOLIDATED STATE, AND ARE CONDUCTED BY KEEPING THE CELL PRESSURE CONSTANT AND EQUAL IN BOTH TESTS, IT CAN BE SHOWN THAT THE RATIO OF RESPECTIVE INCREASES IN OCTAHEDRAL NORMAL STRESS UP TO FAILURE, IN BOTH TYPES OF TESTS WILL BE APPROXIMATELY EQUAL TO A GIVEN FORMULA. IT FOLLOWS THAT A TRUE DIFFERENCE IN VOLUME CHANGES IN BOTH TYPES OF TESTS CAN ONLY BE FOUND IF THE COMPARISON IS RESTRICTED TO A COMMON OCTAHEDRAL PLANE. REFERENCES: VOLUME CHANGES IN TRIAXIAL AND PLANE STRAIN TESTS, W. D. LIAM FINN, NEIL H. WADE, KENNETH L. LEE, ASCE (PROC. PAPER 5611), NOVEMBER 1967.

Volume Changes in Triaxial and Plane Strain Tests

Volume changes occurring in packings of rigid spheres during deformation under both triaxial and plane strain conditions are analyzed theoretically. It is shown that smaller volume changes occur under plane strain conditions for equal axial strain. Experimental data indicate that the result holds true for real soils. The relevance of the result to a study of the strength of soil under high confining pressures is discussed.

Corrections for Strength Test Data

The loads carried by piston friction, rubber membranes, and filter paper drains may have a significant effect on the axial stress in triaxial test specimens. In plane strain tests, friction between the membrane and the plates used to enforce plane strain deformation also influences the axial stress in the test specimens. Failure to correct for these loads results in an overestimate of the axial stress in the test specimens and influences the values of the consolidation pressure, the strength, the strength parameters, the pore pressure parameter, A, and the effective principal stress ratio. Whether test results are to be used in research investigations or for practical purposes, it is desirable to make appropriate corrections to the test data. Techniques for determining values for the various corrections are discussed, and examples of the corrections are given for both triaxial and plane strain tests.

A normal-incidence reflective polariscope for viscoelasticity measurements

A normal-incidence reflective polariscope, together with some auxiliary instrumentation, is described. The instrument consists of eight unit polariscopes, relatively oriented, which are indexed into position within a short period of time to obtain a set of eight data. These data provide sufficient information to separate the principal strains obtained at different time intervals. The primary experimental objective was to design an inflated-cylinder test, analogous to the loading experienced in a solid-propellant rocket, that would enable reasonable measurements of the triaxial surfacelayer strains of a viscoelastic material as a function of time. The stress geometry imposed on the viscoelastic material was that of an unrestricted, biaxially pressurized, thick-walled tubular cylinder. The material investigated was polyurethane solid propellant. Two different methods to reduce the biaxial strains in a low-modulus birefringent polyurethane coating are also described.

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.