Torsional Shear Device Research Articles

A Hollow Cylinder Torsional Shear Device to Explore Behavior of Soils Subjected to Complex Rotation of Principal Stresses

Abstract A hollow cylinder torsional shear device that is modified to simulate more generalized earthquake loading, involving simultaneous compression and shear wave loading in situ, is presented. The nature and degree of stress rotation due to coupled action of compression waves and shear waves are discussed, and illustrative experiments conducted to simulate different loading scenarios in the laboratory are presented. The stress rotation due to this coupled loading is significantly influenced by the initial consolidation stress state and shearing parameters such as the ratio between shear stress and normal stress increments (ΔS/ΔN) and the phase shift (ϕ) between the waves. The representative (ΔS/ΔN) ratios were obtained from the numerical simulations and used in hollow cylinder torsional shear apparatus to investigate the cyclic response of Fraser River sand under the simultaneous action of normal and shear stresses. Typical cyclic test results demonstrating the capability of a hollow cylinder torsional shear apparatus commissioned at Carleton University in following complicated cyclic loading paths are presented in this paper. It is noted that loading under such nonconventional stress paths, such as elliptical and circular paths, could be initiated along different pathways. Cyclic test results along these pathways demonstrate that soil response is dependent on the overall path including the initial stress state. Test results also highlighted the significance of stress rotation and cyclic stress paths in affecting the liquefaction susceptibility of sands.

Drained Shear Displacement Rates in Fully Softened Strength Torsional Ring Shear Testing

Abstract To measure the fully softened strength, the normally consolidated and reconstituted specimen must be drained, i.e., no development of shear-induced pore-water pressures, during shearing. This article investigates (1) typical shear displacement rates in torsional ring shear tests that yield drained shearing conditions for a range of fine-grained soils and (2) the problems that can develop if the porous discs in a torsional ring shear device are not clean and saturated prior to placement of the reconstituted soil paste in the specimen container. The data presented herein show that using a clogged or unsaturated porous disc will require a drained shear displacement rate that is one to two orders of magnitude slower than required, e.g., 0.018 mm/min, if the porous discs are clean, maintained, and saturated as recommended by the original equipment manufacturer and the ASTM D7608, Standard Test Method for Torsional Ring Shear Test to Measure Drained Fully Softened Shear Strength and Stress Dependent Strength Envelope of Fine-Grained Soils.

Natural Rock Fractures: From Aperture to Fluid Flow

Fractures provide preferential flow paths and establish the internal “plumbing” of the rock mass. Fracture surface roughness and the matedness between surfaces combine to delineate the fracture geometric aperture. New and published measurements show the inherent relation between roughness wavelength and amplitude. In fact, data cluster along a power trend consistent with fractal topography. Synthetic fractal surfaces created using this power law, kinematic constraints and contact mechanics are used to explore the evolution of aperture size distribution during normal loading and shear displacement. Results show that increments in normal stress shift the Gaussian aperture size distribution toward smaller apertures. On the other hand, shear displacements do not affect the aperture size distribution of unmated fractures; however, the aperture mean and standard deviation increase with shear displacement in initially mated fractures. We demonstrate that the cubic law is locally valid when fracture roughness follows the observed power law and allows for efficient numerical analyses of transmissivity. Simulations show that flow trajectories redistribute and flow channeling becomes more pronounced with increasing normal stress. Shear displacement induces early aperture anisotropy in initially mated fractures as contact points detach transversely to the shear direction; however, anisotropy decreases as fractures become unmated after large shear displacements. Radial transmissivity measurements obtained using a torsional ring shear device and data gathered from the literature support the development of robust phenomenological models that satisfy asymptotic trends. A power function accurately captures the evolution of transmissivity with normal stress, while a logistic function represents changes with shear displacement. A complementary hydro-chemo-mechanical study shows that positive feedback during reactive fluid flow heightens channeling.

Determination of the interface parameters on the contact of concrete and soil by different methods

The article presents a comparison of tests carried out on torsional and direct shear devices, in order to determine the strength reduction factor on its contact arising between the soil massif and the underground structure. It is necessary to understand which device makes it possible to determine the strength characteristics that are closest to real cases. For the experiments, soft clay and concrete samples were used. The tests were carried out at a vertical pressure of 100 kPa with speeds of 0,005 mm/min and 0,01196 °/min. According to the obtained results, it was concluded that the values of the shear stresses on the torsional shear device are higher than on the direct shear device. This is due to the fact that the contact area is not constant during the test, respectively, the shear resistance decreases. In a number of other works, the differences in the results are attributed to the fact that the mechanisms of collapse differs depending on the type of device. Therefore, it is necessary to study more detailed the conditions of shear and the process of specimen collapse in all devices, which allow one to determine the strength parameters in order to understand which of them gives more correct results.

Discussion of “Correlations for Fully Softened Shear Strength Parameters” by B. A. Castellanos, T. L. Brandon, and D. R. VandenBerge, This Article Was Published in Geotechnical Testing Journal, Vol. 39, No. 4, 2016. [DOI: 10.1520/GTJ20150184

Abstract In this paper, the authors criticize the use of a torsional ring shear device for measuring the fully softened strength (FSS) of fine-grained soils based on problematic ring shear data from Castellanos (2014). This is unfortunate and necessitated taking important time and energy to write this discussion. I have over 26 years of commercial soil testing experience while managing the Woodward-Clyde Consultants and AECOM Technical Services Laboratory in Santa Ana, California. I started performing Bromhead torsional ring shear tests to measure the residual strength (RS) of shear surfaces for landslides in 1991. As Professor Stark expanded his shear strength correlations and the geotechnical engineering practice embraced the use of FSS in stability analyses, I started using the Bromhead torsional ring shear device for FSS testing in 2009. The RS and FSS tests are performed in accordance with ASTM D6467, Standard Test Method for Torsional Ring Shear Test to Determine Drained Residual Shear Strength of Cohesive Soils, and ASTM D7608, Standard Test Method for Torsional Ring Shear Test to Determine Drained Fully Softened Shear Strength and Nonlinear Strength Envelope of Cohesive Soils (Using Normally Consolidated Specimen) for Slopes with No Preexisting Shear Surfaces, test methods, respectively.

Torsional Shear Device for Testing the Dynamic Properties of Recycled Material

Abstract From the viewpoint of environmental preservation and effective utilization of resources, it is beneficial and necessary to reuse wastes, for example, concrete, as the recycled aggregates for new materials. In this work, the dynamic behavior of such aggregates under low frequency torsional loading is studied. Results show that the properties of such artificial soils match with those reported in the literature for specific natural soils.

Cyclic Resistance of a Loose Sand Subjected to Rotation of Principal Stresses

An experimental study aimed at providing insights into the effects of the inclination of principal stress directions with respect to the bedding plane and the role of principal stress rotation on the cyclic resistance of sands is presented. A new hollow cylinder torsional shear device commissioned at Carleton University was used to conduct the experiments in water-deposited Fraser River sand. Specimens at identical initial states were subjected to a constant amplitude cyclic shear stress along loading paths that impose different levels of stress rotation. Cyclic resistance decreased significantly as the maximum orientation of the major principal stress increased to approximately 45°–60°, but it increased with further rotation. This is contrary to the conventional idea according to which the weakest response is expected when the loading causes larger principal stress rotation and/or when the major principal stress is aligned with the bedding planes. The alignment of the plane of maximum shear stress toward and stronger time history of shear stress on the horizontal bedding planes lead to increased liquefaction susceptibility. The nature of shear stress on the bedding planes appears more critical than the alignment of the major principal stress along the bedding planes during cyclic loading. Test results also suggest that cyclic simple shear tests on the basis of stress rotation would represent a lower bound or closer to lower bound resistance. Thus, cyclic simple shear tests provide a convenient means of determining the cyclic resistance and the obtained resistance can be considered a conservative measure if field loading conditions deviate from that in simple shear.

A New Hollow Cylinder Torsional Shear Device for Stress/Strain Path Controlled Loading

An automated hollow cylinder torsional (HCT) shear device has been commissioned at Carleton University to enable research on stress rotation and partial drainage. The design incorporates elements to arrest undesirable runaway strains and enable the capture of post peak strain softening in different directions, and the ability to closely follow prescribed loading paths. This device is capable of applying both static and cyclic loading under stress and displacement controlled loading modes. This is one of the first HCT devices built specifically to study the partially drained response of soils under three dimensional loading. Test results demonstrating various capabilities of this device, and the level of confidence in the measurements are presented in this paper. The presented results highlight the importance of drainage boundary conditions, and principal stress rotation on liquefaction susceptibility. The partial drainage condition in soils reveals that a small expansive volumetric deformation due to unfavorable drainage boundary conditions can trigger strain softening and flow in soils that may be stable and strain hardening under undrained loading. Tests along different total stress paths under three-dimensional generalized loading show that the uniqueness of undrained effective stress path can be extended to generalized three dimensional loading.

Seismic measurements in sand specimens with varying degrees of saturation using piezoelectric transducers

Small-strain seismic measurements in sand specimens were undertaken in the laboratory using piezoelectric transducers. The measurements involved determining both constrained compression wave and shear wave velocities, Vpand Vs, respectively. The piezoelectric transducers were discs (PDs) for Vpmeasurements and bender elements (BEs) for Vsmeasurements. An instrumented triaxial chamber (ITC) was developed and associated support instrumentation was assembled to perform the seismic measurements. The same PDs and BEs were installed in a combined resonant column and torsional shear (RCTS) device. The soil tested in both devices was washed mortar sand. The sand was tested in dry, unsaturated, and saturated conditions in the ITC, while only dry sand was tested in the RCTS. Development, calibration, and operation of the PDs and BEs are discussed. Example waveforms are presented, which are associated with different stress levels, saturation conditions, and frequencies of excitation for P and S waves. A critical factor in performing successful measurements is the driving of each type of piezoelectric transducer at the optimum frequency, which depends on the effective confining pressure ([Formula: see text]), degree of saturation, and soil type. The excitation frequency used for PDs was found to be important when the sand specimens were at nearly or fully saturated conditions.

Modifications of resonant column and torsional shear device for the large strain

Conventional RC/TS (resonant column and torsional shear) devices use a specimen with an aspect ratio (height-to-diameter) of 2:1 and this generates a maximum shear strain in the sample of about 1.5% at the maximum rotation of the driving system. The objective of this study is to modify the RC/TS device to generate higher strain amplitude. The modifications include a new base pedestal to overcome the limitations in the travel of the drive system and modification of the coil wiring to increase torque. The effects of the new coil wire on torque in the electromagnetic drive system were evaluated and the application of the modified device was illustrated using sand soil.

Calibration of Testing Equipment for Reliable Small-Strain Deformation Measurements Using Synthetic Specimens

Abstract For reliable deformation measurements at small strains, calibration of the entire testing system in addition to routine transducer calibrations are very important. Seven synthetic specimens of varying stiffness (4.3 to 1500 MPa) were constructed and tested to measure the compliance of testing equipment and to improve the measurement setups. Testing equipment used in this study included resonant column device (RC), torsional shear device (TS), free-free resonant column device (FF-RC), cyclic resilient modulus testing device (MR) and the static compression testing device. Moduli of synthetic specimens determined by various testing equipment after improvement were almost identical if considered the effect of loading frequency, indicating that all of the testing devices were well calibrated over a wide stiffness range. To verify the effectiveness of calibration on soil testing, two subgrade soils were tested, and moduli determined by various tests compared well. Use of synthetic calibration specimens shows potential for calibrating testing equipment and determining its capability and limitation of small-strain deformation measurements.

Static liquefaction of sands under multiaxial loading

A fundamental study of the undrained behaviour of sands under multiaxial loading is presented. The investigation was carried out using Fraser River and Syncrude sands in a hollow cylinder torsional shear device. Shear loading was carried out under strain control to capture the postpeak strain-softening characteristics of loose sands. It is shown that the undrained response of loose sands is highly dependent on the loading direction. The friction angle mobilized at phase transformation and steady state is a unique material property, independent of the mode of loading, direction of principal stress and initial consolidation stress, and void ratio state. There is no unique relationship between steady state strength and void ratio which is independent of stress path and the level of initial confining stress.Key words: anisotropy, hollow cylinder torsional shear, liquefaction, sand, simple shear, triaxial.

Effect of intermediate principal stress on the deformation response of sand

An experimental investigation of the relevance of the intermediate principal stress (σ2) on the deformation response of a sand is presented. The effects of σ2 are conveniently studied through the nondimensional stress parameter b = (σ2 – σ3)/(σ1 – σ3). A series of stress path tests was performed on Ottawa sand specimens in a hollow cylinder torsional shear device. The experimental program includes shear loading at different values of b, and special b tests, in which b was continuously varied at different stress directions. It is shown that the b value may have a significant influence on the stress–strain response of sand, depending on the loading conditions. Key words: hollow cylinder tests, generalized stress paths, sand, stress–strain behaviour, intermediate principal stress.

Stiffness and strength changes in cohesionless soils due to disturbance

A laboratory and field study of stiffness and strength changes to cohesionless soils due to disturbance has been performed. Laboratory samples were tested in a resonant column torsional shear device. The magnitude of the stiffness loss in laboratory samples was found to be primarily a function of the imposed shear strain amplitude. The time for the stiffness to regain values prior to disturbance also appears to be controlled by the shear strain amplitude. In field tests, decreases in soil strength and stiffness were observed following an explosive detonation in a partially saturated, medium-dense sand. Although there were no measured changes in the soil density, the ground surface elevation, and the dilatometer horizontal stress index, the cone tip resistance and shear wave velocity decreased noticeably. Subsequent time-dependent increases in penetration resistance were observed; however, at certain locations, the increases were not large enough to offset the initial decreases. Comparisons are made between changes in the laboratory and field stiffness values following disturbance, and possible explanations for the behavior are presented. Key words : soil dynamics, disturbance, shear strain amplitude, in situ testing, shear modulus, time effects.

Shear Modulus of Soft Marine Clays

Abstract Instabilities occur frequently in ocean-bottom sediments where the deposition is faster than the consolidation of the material. Cyclic loading of waves contribute to the existing pore pressures within the sediment reducing the effective stresses. The sediment can lose strength and stability and flow in gullies of depth up to 30 m, on slopes less than 0.5 deg. One theory and some related experiments indicate that, depending on the depositional conditions and state of stress, the failure mechanism for such soft saturated marine clays may not necessarily require large straining of the material. Laboratory determination of low-strain shear behavior or shear modulus of soft marine clays can be complicated if high-frequency dynamic testing methods are utilized. Cyclic loading can promote fast degradation of moduli for these soils even at low strain amplitudes. A monotonic torsional shear device, namely a triaxial vane device, was equipped with a computer-aided data acquisition system to detect low-strain shear deformations under quasi-static loading conditions. The average range of electronically measured strain range was 10−4 to 1 percent, which was compatible with that of a high-frequency, low-strain dynamic testing method, namely, resonant column. Comparison of the dynamic and static moduli reduction curves of artificially prepared soft kaolinite specimens demonstrated the cyclic degradation effects on such clays. The relatively continuous, high-resolution low-strain static data indicated further gain in understanding of low-strain nonlinearity and yielding behavior of soft marine clays.

Cyclic Undrained Stress-Strain Behavior of Dense Sands by Torsional Simple Shear Test

ABSTRACT In the first part of the article a review of laboratory cyclic undrained test methods is presented. The features of the cyclic torsional simple shear device which was newly developed to assess the resistance of saturated dense sand against cyclic undrained loading are described. The test results are represented by the relationship between the relative density Dr and the cyclic shear stress amplitude normalized by the effective mean principal stress at consolidation τcy/σ'mc for which a certain value of double amplitude shear strain is observed at a certain number of loading cycles. Cyclic undrained tests were performed for 1) isotropically and anisotropically consolidated specimens, 2) specimens initially sheared and not sheared during consolidation and 3) specimens prepared by different methods, using two different sands, Toyoura Sand, a clean, uniform, fine sand having no fine particles and Sengenyama Sand, a medium fine sand including fine particles to some extent. For any test condition, specimens denser than some critical densities showed extremely high resistances which were much larger than expected from the concept that the cyclic undrained strength be proportional to relative density. For identical values of relative dinsity, loose Sengenyama Sand specimens had strengths similar to loose Toyoura Sand specimens, while dense Sengenyama Sand specimens had strengths much less than dense Toyoura Sand specimens. Loose specimens prepared by the air pluviation method had strengths similar to ones prepared by the wet tamping method, while air-pluviated dense specimens had strengths much lower than wet tamped dense specimens. Other factors affecting the cyclic undrained strength of sands were also investigated. Effects of any factor investigated on the cyclic undrained strength were very large for dense specimens, but only slight for loose specimens.

Cyclic Triaxial Test of Dynamic Soil Properties for Wide Strain Range

Dynamic material properties of soil needed for the nonlinear analysis of earthquake response of the ground have usually been measured in the laboratory using the torsional column shear device. The cyclic triaxial test, despite its easier accessibility and handling for practicing engineers, has seldom been looked upon as a rational way to make a reliable measurement of dynamic properties. In this experimental study a highly sensitive gap sensor and a sealed load transducer are introduced inside the triaxial cell to eliminate the frictions of the conventional displacement sensor and the loading piston. A series of cyclic triaxial tests featuring these improvements have been carried out for saturated Toyoura sand with various void ratios and confining pressures, disclosing the following facts. (i) Reliable measurements of the shear modulus and its strain dependent variation within a wide strain range of the order of 10 -6 to 10 -3 are possible with the improved cyclic loading test, permitting a direct connection with the insitu shear wave velocity. (ii) An essentially good agreement of the modulus is quantitatively recognizable between the triaxial test and the torsional shear test, implying that the different stress and confining conditions inherent to the individual testing devices give no significant effect on the evaluation of the modulus. (iii) This test gives a reasonable hysteretic damping ratio as well as its strain dependency although the damping ratios measured by other researchers with different testing devices widely differ from each other indicating the difficulties for evaluating accurate damping ratio.

Undrained creep characteristics of deep‐ocean sediments

Abstract During this investigation the creep properties of two types of Pacific Ocean marine sediment were studied using the torsional simple shear device. This device is especially well suited for long‐term creep testing of soft marine sediments because it uses short samples (2.54 cm), which results in cost saving and eliminates soil failure under the sample's own weight, as is often the case with triaxial testing. Also, due to the peculiar shape of the test specimen, the torsional simple shear device applies uniform shear strains throughout the soil sample. Both of the above sediments tested during this research lost considerable strength when allowed to creep under stresses greater than their creep limits. A procedure is proposed for determining the time it takes the samples to fail in undrained creep under any stress level greater than their creep limits. It is further shown that the creep behavior of marine sediments is similar to the response of creep‐susceptible terrestrial soils.

Shear Modulus and Damping by Drained tests on Clean Sand Specimens Reconstituted by Various Methods

ABSTRACT Comprehensive tests on a clean sand were performed to evaluate the effects of the methods of sample preparations on shear moduli and hysteretic damping ratios of sands with use of a resonant-column apparatus and a static torsional shear device. All of the tests were conducted under the fully drained condition. Specimens for resonant-column tests were solid cylindrical and those for torsional shear tests were hollow cylindrical. These specimens were sheared torsionally and cyclically. It was found that for a wide range of shear strain the shear modulus and the hysteretic damping ratio of the sand tested by cyclic drained shear tests are quite insensitive to the methods of sample preparations adopted in this investigation. These include the different methods of pouring, compacting, moistening, saturating, unsaturating or so.

Hysteretic Damping of Sands under Cyclic Loading and its Relation to Shear Modulus

ABSTRACT Comprehensive tests were performed to obtain hysteretic dampings of normally consolidated reconstituted sands with use of a resonant-column apparatus and a static torsional shear device. It is shown that there is a simple relationship between the ratio of shear modulus to the shear modulus at very small strain level and damping ratio for sands tested. This relationship is not affected considerably by void ratio and confining pressure for shear strain amplitude from 10-6 to 10-2. For a given value of G/{G}γ = 10-6; the ratio of shear modulus to that at γ = IO-6, the values of damping ratio of clean sands tested are slightly larger than those of other reconstituted natural sands. For these two kinds of sand, average curves representing the relationship between damping ratio and G/{G}γ = 10-6 are shown. These curves can be used for design purposes to evaluate damping ratio of sands from the value of G/{G}γ = 10-6.