Showing papers on "Direct shear test published in 1983"

Mechanics of Fiber Reinforcement in Sand

Abstract: Direct shear tests were run on a dry sand reinforced with different types of fibers. Both natural and synthetic fibers plus metal wires were tested. Experimental behavior was compared with theoretical predictions based on a force equilibrium model of a fiber reinforced sand. Test results showed that fiber reinforcement increased the peak shear strength and limited post peak reductions in shear resistance. The fiber reinforcement model correctly predicted the influence of various sand‐fiber parameters through shear strength increases that were: (1) Directly proportional to concentration or area ratio of fibers; (2) greatest for initial fiber orientations of 60° with respect to the shear surface; and (3) approximately the same for a reinforced sand tested in a loose and dense state, respectively. The findings of this study are relevant to such diverse problems as the contribution of roof reinforcement to the stability of sandy, coarse textured soils in granitic slopes, dune and beach stabilization by pionee...

The losipescu shear test as applied to composite materials

Abstract: A history of the losipescu shear test as applied to composite materials is presented along with a description of the test fixture and specimen design. Iosipescu's shear test is compared to similar test techniques, including the asymmetrical four-point bending (AFPB) test. Finally, in-plane and through-the-thickness shear properties measured using the losipescu shear tests are presented for a variety of materials, including a unidirectional graphite/epoxy, random and continuous-fiber sheet molding compounds, and two polymer materials.

Engineering Behaviour of Rocks

Abstract: 1 Engineering Description of Rocks.- 1.1 Rock testing.- 1.2 Uniaxial or unconfined strength.- 1.3 Empirical field and laboratory tests.- 1.4 Porosity and permeability.- 1.5 Discontinuous rock.- 2 Stress and Strain.- 2.1 Stress at a point.- 2.2 Pore pressure and effective stress.- 2.3 Strain at a point.- 2.4 Representation of stress and strain.- 2.5 Relation between stress and strain.- 2.6 Geostatic stresses.- 2.7 Measurement of in situ stress.- 3 Rock Deformation.- 3.1 Rock tests in compression.- 3.2 Rock deformation in compression.- 3.3 Mechanics of microfracture.- 3.4 Rock macrofracture.- 3.5 The complete rock deformation curve.- 4 Rock Strength and Yield.- 4.1 Rock strength criteria.- 4.2 Yield criteria.- 4.3 The critical state concept.- 4.4 Triaxial testing.- 4.5 Axial and volumetric strain data.- 4.6 The Hvorslev surface in rocks.- 5 Time Dependency.- 5.1 Creep strain.- 5.2 Phenomenological models of creep.- 5.3 Time-dependent deformation.- 5.4 Time-dependent strength reduction.- 5.5 Cyclic loading.- 5.6 Rapid loading.- 6 Discontinuities in Rock Masses.- 6.1 Discontinuity measurement.- 6.2 Discontinuity orientation data.- 6.3 Shear resistance of a rock containing a discontinuity.- 6.4 Shear resistance of a discontinuity.- 6.5 A critical state model for rock discontinuity strength.- 6.6 Measurement of discontinuity shear resistance.- 7 Behaviour of Rock Masses.- 7.1 Discontinuity frequency.- 7.2 Rock mass classification systems.- 7.3 Rock mass strength criterion.- 7.4 The relevance of rock mass strength.- References.- Author Index.

Geotechnical Characterization of Desiccated Clay

Abstract: Conventional testing procedures produce scatter and bias in indicated properties of soils, such as desiccated clays. This paper describes and compares several conventional and non-conventional methods for characterizing the engineering properties of such soils at a site in Houston, Texas. Properties considered include undrained shear strength, stress-deformation moduli, earth pressure coefficients, and compression indexes. Similarities and differences between soil preconsolidated by desiccation and by stress removal are noted.

Shear Resistance Enhancement of 1.22-Meter Diameter Soil Cross Sections by Pine and Alfalfa Roots

Abstract: Plant roots have been shown to increase soil shear resistance through direct mechanical reinforcement and thereby enhance soil stability on slopes. Because of their potential large diameter and length, the roots of trees may be especially significant in such soil reinforcement. To provide large rooting volumes simulating natural conditions and shear cross sections many times larger than potential tree root diameters, we constructed 12 1.22- by 1.22-m cylindrical soil containers in which two artificial soil profiles were prepared. Replicates of each profile type were planted to alfalfa, yellow pine, or were kept clear of plants. A large pneumatic direct shear device sheared both root-free and root-permeated materials along a horizontal plane at the 0.6-m depth at either constantly maintained shear stress levels (creep shear) or at constant shear displacement rates. Creep shear at the 0.6-m depth showed that roots of 14-month-old alfalfa increased the shear resistance of homogeneous clay loam and a clay loam/gravel interface simulating a soil-weathered rock boundary by 32 and 50%, respectively. Constant shear displacement rate experiments at the same depth on similar samples permeated by roots of yellow pine planted 54 months earlier showed shear resistance increasing steadily with displacement over the entire test displacement range. At 75 mm displacement, the shear resistance of the pine-rooted soil was about two times that of the nonrooted in both profile types. The superiority of pine roots to alfalfa roots in increasing soil shear strength in these experiments is in accord with field observations that woody plants are more effective than herbaceous plants in stabilizing soil against slips and slides. Pine root-size distributions determined 11 months after the last shear test were combined with root tensile strengths and Young's moduli previously measured and used in model simulations of root reinforcement with good results.

In-plane shear test of thin panels

Abstract: Efficient application of thin-gage composite materials to helicopter fuselage structures necessitates that the materials be designed to operate at loads several times higher than initial buckling load Methods are required to accurately measure and predict the response of thin-gage composites when subjected to these loads This paper presents the results of an analytical and experimental study of the behavior of thin-gage composite panels subjected to in-plane shear loads Finite-element stress analyses were used to aid in the design of an improved shear fixture that minimizes adverse corner stresses and tearing and crimping failure-modes characteristic of commonly used shear fixtures Tests of thick buckle-resistant aluminum panels and thin aluminum and composite panels were conducted to verify the fixture design Results of finite-element stress and buckling analyses and diagonal-tension-theory predictions are presented Correlation of experimental data with analysis indicated that diagonal-tension theory can be used to predict the load-strain response of thin composite panels

Direct shear failure in reinforced concrete beams under impulsive loading

Abstract: : An analytic procedure is developed, using classic elastic Timoshenko beam theory, to define conditions under which reinforced concrete beams and one- way slabs can fail in a direct shear mode when subjected to distributed impulsive loading. The procedure is based on the assumption that incipient failure occurs in direct shear when the beam support shear exceeds a strength threshold before the support bending moment attains its ultimate capacity. The Timoshenko theory is extended to include rotational beam-end restraint and to account for viscoelastic material response to assess qualitatively the influence of rate effects on shear and bending moment. Dynamic failure in direct shear is presumed to behave in accordance with currently accepted static shear transfer mechanisms. Dynamic failure criteria are extropolated from static criteria with the use of an enhancement factor based on increased material strengths due to load rate. Failure curves, defining peak pressure versus rise time domains where direct shear failure is possible, are compared to experimental evidence for specific beam geometries and load rates. Post failure deterministic and stochastic models are introduced as candidates for analysis beyond incipient shear failure. It is concluded that direct shear failures can be predicted for certain combinations of load parameters. Rate effects enhance shear forces more than bending moments during transient response. Strength enhancement due to load rate reduces the domain of load parameters over which a direct shear failure can take place, whereas a relaxation of beam-end restraint increases this domain considerably.

A comparison of alternative methods of measuring the residual strength of london clay

Abstract: This paper describes a series of consolidated drained direct shear tests on natural shear surfaces in London clay to determine the residual shear strength, and compares the results with those obtained in ring shear tests on the same soil. (Author/TRRL)

Effect of rate on soil shear strength and soil-metal friction I. Shear strength

Abstract: The effect of deformation rate on the shear strength of a sandy and a clay soil has been examined in a new laboratory rig designed to shear soil in the range equivalent to 0.0015-5 m/s sliding speed. Soil cohesion was found to vary logarithmically with deformation rate over a wide range of moisture contents. The soil internal friction angle was independent of deformation rate and the residual shear strength did not vary in a consistent manner with deformation rate. The results have important bearing on the efficiency of soil working operations such as cultivation, earth moving and traction.

A laboratory investigation of grid reinforcements in clay

Abstract: The governing criteria for internal stability of reinforced soil require that the soil reinforcement should have adequate factors of safety against tensile fracture and pullout. In terms of total stress the pull-out resistance will be some function of the area of reinforcement embedded in the restraint zone and the soil-reinforcement adhesion that may be related to the undrained shear strength of the soil by an adhesion factor. This factor has been assessed for several types of reinforcement using a direct shear box with the reinforcement inclined across the two halves of the box. These tests showed grid reinforcement to be the most efficient, consequently, subsequent testing, in the form of pull-out and shear box tests with horizontal reinforcement, was restricted to grids. The adhesion factors were found to be markedly dependent on test method with the pull-out test giving the lowest values. An analytical assessment of the results suggests that grid pull-out resistance is a function of the area of grid members normal and parallel to the direction of applied load rather than embedded plan area.

Influence Of Shear Velocity On Rock Joint Strength

Abstract: The influence of the rate of shear displacement on the frictional resistance of rock discontinuities was examined by testing jointed samples of three rock types in a dynamic direct shear machine. The influence of rock type, joint roughness, apparent area of contact, normal stress level and gouge infilling were investigated. The experiments consistently showed that the frictional resistance is dependent on the slip velocity. This rate-dependency was observed within a certain rate of shear velocities below and above which the frictional resistance was essentially independent of the rate of shear displacement. A model based on mechanical instabilities is proposed to explain the observed behaviour. The number of the covering abstract of the congress is TRIS no. 385148. (Author/TRRL)

Proper Test Conditions for Measurement by a Direct Shear Tester With Parallel Plates

Abstract: The effects of the dimension of a movable plate, the twist condition and the roughness of the surfaces of the movable plate and fixed plate in contact with the powder on the powder yield locus (P. Y. L.) measured by a direct shear tester with parallel plates are examined.From the results, the proper experimental conditions are as follows:1) The dimension of the movable plate have an effect on P. Y. L., and so the suitable dimension for measurement are determined.2) A normal stress of about 0.28kPa is suitable for the twist.3) The surfaces of the movable plate and fixed plate have an irregular roughness like sand paper which is better than a surface which has a regular roughness, such as notching.Furthermore, as a result of measuring several powders at the above proper conditions, . it is recognized that fc/γg is more suitable to evaluate the flowability of powders than σp/fc.

Cyclic Behavior of Sand During Rotation of Principal Stress Axes

Abstract: Synopsis By the use of a triaxial torsion shear test apparatus, statically operated cyclic loading tests were conducted on loose saturated specimens of the Japanese standard sand. The stress difference between the axial and horizontal stresses as well as the torsional shear stress was cyclically applied to the test specimens so that the continuous rotation of the principal stress directions could be achieved during the cyclic loading. The test results showed that, even when the amplitude of the combined shear stress (deviator stress) is maintained constant, the plastic deformation as represented by the pore water pressure build-up and progressive accumulation of volumetric strain could take place in the sand, if the rotation of the principal stress axes is executed during the cyclic loading.

Vane shear strength testing

Abstract: A description is given of the vane strength testing procedure, the equipment used and the interpretation and use of results.

A compact shear test specimen

Abstract: Breve presentation sur la mecanique de la rupture de materiaux en beton. Resultats pour le beton non arme et beton avec fibre de prolypropylene

Strength of Anchor Bolts in Grouted Concrete Masonry

Abstract: This paper reports the strength and behavior of various diameter J-shaped bolts embedded in concrete masonry. The bolts were tested monotonically, in direct tension, direct shear, and in combined shear and tension. The results of the monotonic tests show that for the combined shear and tension and for tension tests, strengths of the embedments increased with bolt size up to the 3/4–in. (19 mm) diameter. For larger diameter bolts, the masonry began to fail resulting in approximately equal strengths for increasing bolt diameter. The strength of bolts in shear was found to increase with bolt size as long as the bolt was pretightened sufficiently.

Soil remolding and sensitivity measurements

Abstract: This study examines the problem of measurement of soil sensitivity and the significance of soil remolding effects on the "remolded" strength of soil. A simple shear device has been adapted to provide a means for both soil remolding and continuous measurement of shear stress and strain using cyclic stress reversals. Computations can be made to relate soil remolding and input energy for correlation with measured remolded soil strength using the simple shear device. (Author)

Direct Shear Strength of Appalachian Coal

Abstract: A total of 142 prismatic specimens were prepared from 5 different Appalachian coal seams for direct shear-strength tests. Two types of specimen fracture were observed. The shear stress versus shear displacement and normal displacement for each specimen were recorded and analysed. Two linear regressions were derived for best fitting the shear failure of the coal.

In situ and laboratory shear devices for rock: a comparison

Abstract: : Shear strength parameters were measured using an assortment of testing devices. The results were compared and contrasted. The devices included machines routinely used by the U.S. Army Corps of Engineers and several machines with new or unusual features. The tests were performed on rock simulant and Rangely sandstone. The tests on rock simulant used specimen suites that included smooth cast joints, joints with asperities, and intact material. The tests on the Rangely sandstone were performed on clean discontinuities. All tests on the rock simulant were performed in the laboratory. One of the test suites on the sandstone was performed in situ; the remainder of the tests were performed in the laboratory. The tests showed substantial differences in strength parameters due to test machine details. The study demonstrated the need for a reliable direct shear device capable of testing 60-in.-diam core.

Buckling and failure characteristics of graphite-polyimide shear panels

Abstract: The buckling and failure characteristics of unstiffened, blade stiffened, and hat stiffened graphite-polyimide shear panels are described. The picture frame shear test is used to obtain shear stress-strain data at room temperature and at 316 deg C. The experimental results are compared with a linear buckling analysis, and the specimen failure modes are described. The effect of the 316 deg C test temperature on panel behavior are discussed.

The magnitude of displacement along clay mylonite shear zones

Abstract: In 1970 Stimpson & Walton reported on the presence of thin clay bands, tentatively (and perhaps inappropriately) named ‘clay mylonites’, in core recovered from the Northumberland and Durham Coalfield, England. The geotechnical properties of these layers were investigated and the results reported at the First International Congress of the International Association of Engineering Geology in Paris. Apart from the low direct shear strengths of these thin layers and the excellent drilling and careful core logging that must be undertaken in order to detect them, the most scientifically interesting aspect of the laboratory test data was a relationship between the thickness of the ‘clay mylonite’ and its shear strength (Fig. 1); the thicker layers had a greater shear strength than the thinner layers. A possible model to explain this feature is to consider the shear zone as comprising a series of parallel surfaces stacked one upon the other, each of which undergoes some shear displacement. The total shear displacement of the shear zone is the sum of all the internal shear displacements. According to this model, a thin layer would have fewer internal surfaces and, hence, for the same total shear displacement each internal surface would suffer a greater displacement than in a thick clay mylonite. Thus, it would be anticipated that a thin clay mylonite would have a lower shear strength than a thick clay mylonite, i.e. it is closer to its ultimate shear strength. The magnitude of displacement along the clay mylonite bands is a matter of

A method to evaluate the deformation behaviour of discontinuous rock mass and its applicability

Abstract: A method to evaluate the deformability of rock masses is presented. This method considers the geometrical and mechanical properties of discontinuities, and the mechanical properties of intact rock. The constitutive equations to represent normal joint and shear stiffnesses varying against stress-deformation are introduced. The applicability of this method is clarified by means of two-dimension loaded large-scale rock mass models in the laboratory and by numerical analysis. The number of the covering abstract of the congress is TRIS no. 385148. (Author/TRRL)