Showing papers on "Direct shear test published in 1990"

The orientation of shear bands in biaxial tests

Abstract: Shear band formation in planar deformation of soil samples is studied theoretically to explain the experimental finding that orientation angles depend on particle sizes. A review of such data shows that steep Coulomb-type shear bands occur in fine sands, whereas less inclined Roscoe-type shear bands are observed for coarse material. A bifurcation analysis for the onset of shear-banding appears to be non-decisive, as all orientations within the RoscoeXoulomb range are found to be admissible. The new element of this theoretical analysis is that the material outside the shear band is allowed to unload elastically. Hereafter the analysis is extended to the post-peak regime. Postpeak, the Coulomb-type sbear band appears to be the weakest failure mode with the lowest residual strength. This explains the frequent occurrence of such shear bands. However, Coulomb-type shear bands are shown to involve stress discontinuities which can hardly occur in samples of coarse sand. This explains the occurrence of Roscoe-typ...

Shear Strength Characteristics of Sand‐Polymer Interfaces

Abstract: The results are summarized for an experimental program involving over 450 direct shear tests of sand‐polymer interfaces. The interface frictional strength was found to increase with soil density and decrease with the Shore D Hardness of the polymer. The shear strength characteristics were found to vary as a function of the type of sand, but were independent of repeated loading, at least insofar as polyethylene piping and linings are concerned. The shear strength characteristics of a polymer interface can be expressed conveniently as the ratio of the interface angle of friction and the direct shear angle of soil friction, δ/ϕds′. This ratio was relatively constant at 0.55–0.65 along high‐ and medium‐density polyethylene surfaces for different types of sands at various densities. A general model for interface frictional resistance is developed, in which δ/ϕds′ is related to the Shore D Hardness, HD, of the polymer. Limiting conditions for δ/ϕds′ are defined on the basis of theoretical considerations involvi...

Kettleman Hills Waste Landfill Slope Failure. II: Stability Analyses

Abstract: Analyses were made to determine the cause of a stability failure of a 90 ft high, 15 acre hazardous waste landfill in which lateral displacements of up to 35 ft and vertical settlements of up to 14 ft were measured. The failure developed by sliding along interfaces within the composite geosynthetic‐compacted‐clay liner system beneath the waste fill. The shear resistances of the different interfaces in the liner system were determined by direct shear and pullout tests as described in a companion paper (Mitchell et al. 1990). Conventional two‐dimensional (2D) stability analyses of representative cross sections and three‐dimensional (3D) analyses of the overall waste fill and liner configuration are described. Each type of analysis was applied to two cases: (1) The “Probable Minimum Clay/Liner Wetting Case,” in which shear along a wetted HDPE liner/compacted clay interface was assumed to occur only over a small area of the base; and (2) the “Full‐Base‐Wetting Case,” in which the HDPE liner/compacted clay lin...

In‐Plane Resistance of Reinforced Masonry Shear Walls

Abstract: Flexural and shear strengths of reinforced masonry shear walls are examined, based on experimental results obtained from 22 6-ft. by 6-ft. masonry wall specimens. These results are summarized and current design formulae examined. It is found that the simple flexure theory based on the plane-section assumption can be applied to square wall panels with good accuracy. Moreover, it appears to be consistently conservative. The 1988 Uniform Building Code specifications for the shear strength tend to be very conservative for the square wall panels studied and less conservative for walls with lower aspect ratio. Furthermore, the code specifications tend to overestimate the shear strength contributed by the horizontal reinforcement and neglect the influence of axial stress. Hence, a new shear formula that takes into account the influence of axial stress and flexural reinforcement is proposed. The formula appears to have good correlation with experimental results obtained in this study as well as those of others.

Laboratory Measurement of Small Strain Shear Modulus Under K0 Conditions

Abstract: A new device to measure the small strain shear modulus (Gmax) under a no lateral strain condition has been developed. The techniques for measuring Gmax are discussed, with emphasis on bender element techniques. The performance of the bender elements are compared with results from simultaneous resonant column tests. An in-depth description of the lateral stress measurement system, the Gmax determination technique, and the measurement of vertical strain is presented along with representative test results to demonstrate the performance of the device.

Evaluation of shear strength of fibre-reinforced concrete beams

Abstract: A method is proposed to calculate the ultimate shear strength of fibre-reinforced concrete rectangular beams without stirrups. The method shows good agreement with published test results of 89 beams which failed in shear. The published data were also used in a regression analysis to identify the factors influencing the shear strength of fibre concrete beams. These factors were found to be the shear span-to-depth ratio, main reinforcement volume, dimensions, and type. Two formulae are presented to predict the cracking and ultimate shear strength and these show good correlation with published test results.

Evaluation of Testing Techniques for the losipescu Shear Test for Advanced Composite Materials

Abstract: The purpose of the study was to explore and subsequently establish ex perimental techniques for the losipescu shear test method for advanced composite materials. For the preparation of notches in the Iosipescu specimens it was found that con ventional machine cutting tools could be used provided that the base of the notch was in spected for micro-damage. The occurrence of a pure shear strain field in the test section was evaluated by separately monitoring the readings from the tension and compression strain gauges. Grinding of the four loading surfaces of the original University of Wyoming test fixture was required to eliminate in-plane or out-of-plane bending or twisting of the specimen. A state of pure shear strain (as defined by equal readings from the tension and compression gauges) can be produced in 90 degree but not 0 degree original Iosipescu specimens when tested in the original University of Wyoming fixture (when the loading surfaces were ground smooth and parallel). In terms of analysis of the ...

Rheology of polycarbonate/linear low density polyethylene blends

Abstract: The flow behavior of linear low density polyethylene blended with polycarbonate (LLDPE/PC) was studied at 245°C using an Instron Capillary Rheometer and a Rheometrics Mechanical Spectrometer. The capillary measurements were repeated several times for each crosshead speed and capillary. The averaged values were corrected for shear heating as well as the pressure, entrance-exit, and power-law fluid effects. In spite of the utmost care, blend results were erratic with a standard deviation of 25 to 35 percent. Analysis of the capillary data suggested a telescopic flow with the lower viscosity component of the blend migrating toward the capillary wall. The experimental difficulties resulted from the flow and time induced variations of blend morphology. By contrast, the dynamic shear test results were found to be rapid and reproducible with a standard deviation for the complex viscosity of blends not exceeding four percent. The shear moduli of blends indicated the presence of an apparent (time dependent) yield stress, originating from interaction between domains of the dispersed phase. At frequencies exceeding a critical value, shear coalescence of the dispersed phase was observed near the rim of the rheometer plates.

Shear Properties of Pultruded Glass FRP Materials

Abstract: The in‐plane shear modulus and the in‐plane shear strength of pultruded glass fiber reinforced plastic (FRP) materials were measured using the Iosipescu shear test method. Material specimens, in coupon form, were cut from the webs and flanges of commercially produced polyester and vinylester wide‐flange pultruded beams. The experimental testing procedure is described, and data reduction methods needed to define the shear modulus and the shear strength from the nonlinear stress‐strain curves are discussed. A new method to obtain the in‐plane shear modulus directly from load‐displacement data is proposed. Shear modulus predictions using the proposed method are compared with those obtained from the stress‐strain data.

A Method for Uniform Shear Stress-Strain Analysis of Adhesives

Abstract: The adaptation of the Iosipescu test as a method for determination of the stress and strain to failure and the shear modulus of adhesives under uniform shear conditions is described. The design and performance of a number of special purpose instruments and jigs to facilitate sample preparation, bond line thickness measurement, and shear displacement determinations are also described. Representative shear stress-strain curves of a nylon-epoxy film adhesive are presented.

Evaluation of the V-Notched Beam Shear Test Through an Interlaboratory Study

Abstract: In recent years two notched beam flexure tests, the Iosipescu and the asymmetric four-point bending (AFPB) methods, have been proposed for the measurement of shear stress-strain behavior and shear strength of fiber reinforced composite materials. The methods have made significant inroads into the testing community for continuous, woven fabric and discontinuous fiber composites, and a test standard is being developed in ASTM Committee D-30. This paper describes the test methods and summarizes the results of a round-robin test program to define the within- and interlaboratory precision and bias.

Centrifuge modelling of cone penetration testing in cohesionless soils

Abstract: The quasi-static cone penetration test is becoming increasing popular as a site investigating tool to determine the geotechnical parameters for geotechnical design. As the result of complex changes in stress strain relationship, no comprehensive theoretical solution to this problem has yet been developed. Many of the available interpretations of cone penetration data are made with empirical correlations to obtain the required geotechnical parameters. 50 centrifuge tests at elevated g and 52 laboratory tests at Ig together with 23 triaxial tests with cell pressure ranging from 25kPato lOMPa to determine the mobilised angle of shearing resistance and 13 direct shear tests to determine the friction angle of cone-soil interface were carried out. The penetration test results show that the stress level and the density of the soil are the most important factors that govern the penetration resistance. Three different diameter cone penetrometers were employed in the investigation, i.e 6.35, 10.0 and 19.05mm which when tested on the same specimen such that they simulated a 'common prototype' of 400mm diameter in general gave an excellent "modelling of models" correlation. Experimental results show that no grain size effect on cone resistance was observed for dB greater than 12 where B is the cone diameter and dso is the nominal grain &0 size, whereas for dB = 7.5, the grain size effect begins to appear and the difference on &0 cone resistance is approximately 10% at ~ = 25 where D is the depth of penetration. The data indicate that difference in tip resistance between same sizes of cones but with quite different surface roughness, i.e knurled (rough) and unknurled (smooth) cones, is negligible for three different nominal grain sizes of sand (B.S 14/25, 25/52, 52/100 Leighton Buzzard sand). The data indicate that the rate of penetration does not significantly affect the tip resistance in dry sand where no excess pore pressure has been generated. The distance of the cone from the bottom boundary at which the bottom boundary effect becomes evident depends on the diameter of cone and the relative density of the soil and can be approximated from an empirical correlation as ~ = 0.1139(R.D%) - 1.238 where X is the distance from the bottom boundary. Correlation of the test results were carried out using :- ·the conventional approach to relate the tip resistance qc, (Tv and the relative density R.D . • the state parameter approach to relate the state parameter tP' and the normalised factor of the tip resistance by mean normal effective stress [~] 0.5. Armed with these correlations, they can be used to determine the fundamental soil properties such as mobilised angle of shearing resistance for design or alternatively, to determine the insitu density of a model test sample such as is employed in a centrifuge test. The theoretical solution to the deep penetration problem has been analysed using the method of characteristics taking into consideration the penetration up to a characteristic depth, thereafter a modified spherical cavity expansion theory is more appropriate. Classical bearing capacity theories used by other researchers are discussed. A parametric study on the effects of soil compressibility ~ has also been carried out for deep penetration.

Evaluation of In Situ Effective Shear Modulus from Dispersion Measurements

Abstract: A procedure is described for evaluating shear modulus depth profiles of uniformly deposited soil strata. The method combines steady-state vibration techniques for subsoil exploration and results from the analytical treatment of surface wave propagation problems in an elastic half-space with depth-depending stiffness. The model proposed covers a wide range of real soil deposits. The shear modulus variation with depth is obtained from the measured dispersion curve by assigning the surface wave velocity to the soil conditions at a depth of 0.3 times the wavelength.

Strain Compatibility Analysis for Geosynthetics Reinforced Soil Walls

Abstract: The methods currently used for the design of reinforced earth walls with extensible geosynthetic reinforcements can be broadly classified as: (1) Working stress design methods that basically rely upon restrictive assumptions with regard to the state of stress in the soil; and (2) limit equilibrium methods that essentially use conventional slope stability analyses, modified to account for the reinforcement effect on the global stability of the reinforced soil mass. Neither of these approaches considers the fundamental requirement of strain compatibility between the reinforcement and the soil nor can they provide any evaluation of the effect of soil dilatancy and extensibility of the reinforcement on the mobilized tension forces and structure stability. This paper presents a strain compatibility design approach that is fundamentally based on the analogy between the plane strain shear mechanism that develops along a potential failure surface in the actual structure and the response of the reinforced soil material to simple shearing. The soil-reinforcement load transfer model used in this analysis allows for the evaluation of the effect of soil dilatancy and extensibility of the reinforcement on the generated tension forces and on the probable location of the potential failure surface.

Geotechnical Properties of Expanded Shale Lightweight Aggregate

Abstract: In recent years lightweight aggregates are being used increasingly in geotechnical applications. This paper presents results of large-size one-dimensional compression and direct shear tests performed on lightweight aggregate. The compressibility and shear strength characteristics of the lightweight aggregate are compared with those of normal-weight aggregate using the same experimental setup. Results of the direct shear tests performed to determine the angle of friction between the geotextile and lightweight aggregate are also presented. In addition, static shear modulus values as determined from model pile tests are presented and compared with those reported for normal weight aggregates.

The performance of soil reinforcement in bending and shear

Abstract: Previous experimental studies of soil-reinforcement interaction have generally concentrated on the effect of reinforcement working in axial tension; this study looks at reinforcement working in bending and shear. The experimental programme was carried out in a large scale direct shear apparatus able to contain a cubic soil sample of side 1m. A previous study showed that the apparatus required improvements to its boundaries. Modifications to the apparatus resulted in a significant improvement in the performance of the apparatus. The data being comparable with those from direct shearboxes with similar symmetrical boundary conditions. The effect of reinforcement in shear and bending was studied by varying the reinforcement cross section reinforcement orientation, method of installation, and the relative soil- reinforcement stiffness and strength. All tests were carried out on a well graded and uniform quartz sand. The reinforcement was typically mild steel circular bar. Data from tests on instrumented reinforcement bars allowed the distribution of lateral loading to be observed. This led to the development of a mathematical model for predicting the shear force available from reinforcement in soil. A comparison of this model with the test data and from data in the literature revealed it to provide an accurate upper estimate of reinforcement shear force are much greater than those required for axial force. The conclusions in this dissertation address much of the ambiguity over the use of soil reinforcement in shear and bending for soil nailing and dowelling design.

Velocity-dependent friction in a large direct shear experiment on gabbro

Abstract: Abstract Velocity-stepping sliding experiments on a 0.1 m2 interface between two gabbro blocks under 0.5–2.0 MPa normal stress have shown consistent velocity-weakening behaviour. The parameter values are in a similar range to those measured on other materials in other laboratories. However, simulation of the complete transient behaviour requires a second state-variable which has a characteristic decay distance c. 100 × longer than the first, and with the opposite sign (velocity-strengthening). The second delayed effect is not sufficient to cancel out the short period effect, and is not expected to control the onset of unstable stick-slip sliding. These experiments extend the observed realm of velocity-weakening behaviour to larger interfaces and lower normal stresses than has been previously reported.

The Iosipescu shear test method as used for testing polymers and composite materials

Abstract: This paper describes a shear test method for polymers and composite materials, based on the Iosipescu (1967) shear test which was originally developed for use with homogeneous isotropic metals. Special attention is given to the loading fixture for the test, the standard specimen design and shear stress measurements. The range of the test applications is indicated. The method is in the final stages of being accepted as an ASTM standard.