Cylindrical Shear Research Articles

Is There any Effect of Sample Sizes on Laboratory Liquefaction Tests?

Determination of liquefaction potential of sands in laboratory; dynamic three axial, hollow cylindrical torsional shear, resonance column, bender elements and cyclic simple shear tests are used. In this study, the effect of sample size on the determination of liquefaction energy of sandy soils in cyclic simple shear test apparatus was investigated. Uniform clean sea sand was used in the study. The cell inner diameter in which the samples to be tested is placed is 50 mm. Samples were prepared three different sizes with a length/diameter (H/D) ratio of 1, 0.5 and 0.25 and four varied relative densities (Dr: 40%, 50%, 60% and 70%). The samples were subjected to 1D cyclic loading at a frequency of 0.1 Hz under 100 kPa vertical stress and 50 kPa pore pressure. Each experiment was repeated 3 times, with equivalent or closer results considered significant. According to the test results, the liquefaction energy values per volume (J/m3) of the samples of different sizes are different from each other.

Anisotropy in Sand–Fibre Composites and Undrained Stress–Strain Implications

Among the plethora of studies on anisotropy in fibre-reinforced sands, there exist conflicting views on effects on the steady-state deformations of initial packing. These conflicting views are further confused by strictly limited experimental evidence on flow in complex loading environments where the principal stresses rotate whereby shearing and torsional stresses combine, and when extension in soil relieves the compressive stresses. In the heuristic of intrinsically anisotropic nature of the soil and in recognition of the inability of placement methods to overcome such anisotropy, this paper aims to use the orientation of principal stress and soil initial packing state combined as proxy parameters to further the knowledge of plastic behaviour in fibre-reinforced sands. This study furthers the knowledge of the dependency of steady states on anisotropy in composite geomaterials. In doing so, the direction of principal stress orientation is varied from 15° to 60° (from vertical axis), taking an intermediate principal stress ratio of 0.5 and 1.0 and two initial confining pressures. Twenty-four undrained torsional shear tests are conducted using a hollow cylindrical torsional shear apparatus. Under compression and plain strain conditions, torsional stresses limit the improvements in soils’ undrained shear strength upon fibre reinforcement. Extension in soil remarkably increases fibres’ contribution to betterment of undrained strength. Fibres are least effective under low isotropic confining pressures and also for certain ranges of torsional stresses.

Post-cyclic volumetric strain of calcareous sand using hollow cylindrical torsional shear tests

Post-cyclic settlement of saturated soil, due to dynamic loadings such as earthquake, causes severe damage to structures. Dissipation of excess pore water pressure generated during cyclic loadings results in the volumetric strain of soil materials. Many studies have been conducted on factors affecting post-cyclic volumetric strain (εre,v) of siliceous soils. The effect of important factors on post-cyclic settlement of calcareous sand is evaluated in this study. Calcareous soils are generally located in tropical and subtropical areas near oceans and gulfs. These deposits are usually saturated and consequently, post-cyclic settlement can be critical in these sediments. In this research, a series of hollow cylindrical torsional shear tests were performed on Hormuz calcareous sands obtained from the north coast of the Persian Gulf. The samples were loaded cyclically under different cyclic stress ratios (CSRs) in undrained condition and then, terminated at a desired pore water pressure ratio (ru). After that, the excess pore water pressure was allowed to dissipate, and volumetric strain occurred as a result. The effects of relative density (Dr), cyclic stress ratio (CSR), excess pore water pressure ratio (ru) and maximum cyclic-induced shear strain (γmax) on εre,v of the reconstituted sand were evaluated. The results showed that maximum shear strain is the most effective factor in estimating the post-cyclic settlement of the calcareous sand.

Rate dependence on mechanical properties of unsaturated cohesive soil with stress-induced anisotropy

The strain rate during shearing has been shown in experimental studies to strongly affect the mechanical behaviour of soil. For saturated soil, sufficient knowledge has been obtained to achieve equilibrium conditions for the pore water pressure. Nevertheless, little is known about unsaturated soil. Therefore, this study used a hollow cylindrical torsional shear apparatus to investigate the rate dependence on the deformation and strength properties of unsaturated soil. First, unsaturated specimens were anisotropically consolidated with different directions of major principal stress to assess the rate dependence of the anisotropic behaviour. Then, the shear stress was removed to produce an isotropic stress state. Shearing was applied using the specimens to evaluate the strain rate effects on the mechanical properties of unsaturated cohesive soil. The results indicate that the secant shear modulus increased with the strain rate in both constant suction (CS) and constant water content (CW) conditions. The shear strength did not change with the strain rate under a CW condition, but it decreased with the strain rate under a CS condition.

Effects of inter-helix spacing and short-term soil setup on the behaviour of axially loaded helical piles in cohesive soil

Axial compressive load tests performed on piles instrumented with strain gauges were completed in order to investigate the effects of inter-helix spacing on the behaviour of helical piles. The test piles had two helices with varied values of helix spacing. The helix-bearing soil layer consisted of a homogeneous clay with an average undrained shear strength of 65 kPa. The test pile failure mechanisms were determined by comparing the measured load distributions to the distributions predicted by the individual bearing and the cylindrical shear models. The results suggest that the individual bearing model dominates the pile behaviour for piles with an inter-helix spacing to helix diameter ratio greater than or equal to 1.5. The helix bearing capacity factor and the shaft adhesion factor were evaluated by comparing the measured pile component resistances to the theoretical estimations. The back-calculated bearing capacity and the adhesion factors were below the values traditionally used in helical pile design. The effects of the soil setup on the pile behaviour were evaluated by comparing the load-settlement response of a pile tested immediately after the pile installation to equivalent piles tested many days after the installation. A piezometer installed near the upper helix edge was used to measure the excess pore pressure generation and dissipation induced by the installation. The results suggest that the pore pressure generation induced by the pile installation was minimal and had little influence on the short-term ultimate capacity.

Water Content–Density Criteria for Determining Geomembrane–Fly Ash Interface Shear Strength

The aim of the present paper was to determine shear strength at the interface between fly ash, as a material underlying artificial sealing layer of storage yards, and HDPE geomembranes. The fly ash was compacted at moisture contents ranging over optimum water contents ± 5% using the standard Proctor test. The shear strength and interaction tests were conducted in classic direct shear apparatus with a cylindrical shear box. For interface strength tests the bottom box frame was equipped with a polycarbonate platen, which enabled geomembrane fixing. The shear strength of the interface contact of fly ash–smooth HDPE geomembrane did not greatly depend on moisture at compaction; however, it was important for textured geomembrane. The lowest interface strength was obtained at the highest moisture w= wopt + 5%, and the greatest values at moistures w ≥ wopt, for both geomembranes.

Modelling and numerical simulation of n-heptane pyrolysis coking characteristics in a millimetre-sized tube reactor

Based on the optimization of the recently proposed gas phase mechanism for n-heptane pyrolysis, mechanisms for polycyclic aromatic hydrocarbon (PAH) formation and a detailed wall surface reaction, a basic gaseous pyrolysis mechanism with 1127 steps and a simplified surface reaction mechanism with 34 steps were developed, respectively. After performing the detailed estimation and modelling procedures for the surface site density (SDEN) related to the particle diameter, particle density, C/H ratio and other parameters determined by the experimental tests and observations, numerical studies were integrated with the developed coke model to simulate the pyrolysis process and the coking properties in a millimetre-sized tube reactor on the Chemkin Pro software platform using a two-dimensional cylindrical shear flow (CSF) module. The prediction values of the pyrolysis product concentration and coking rate at different temperatures were compared with the experimental data, and agreement was obtained. Under pyrolysis conditions of an n-heptane inlet flow rate of 0.5 ml/min, an operating pressure of 1.0 MPa and a furnace temperature of 973–1073 K, the research results showed that the hydrogen abstraction reaction, as the first and key step of coke formation, is easily affected by gaseous diffusion. As the temperature and particle diameter increase, the inhibition of diffusion becomes stronger. Among all the considered radicals, the abstraction ability of the H radical is the strongest, and it is easily restricted by diffusion. The presence of abundant radicals such as CH3, C2H3, and C3H5 at low temperatures can compensate for this limitation. For the unsaturated species addition reactions, the calculation results showed that the addition of olefins, alkynes, diolefins and aromatic hydrocarbons occurs in sequence with an increase in residence time. With increasing temperature, the addition contributions of olefins such as C2H4 and C3H6 gradually weaken, while those of small molecule aromatic hydrocarbons such as benzene (A1) and styrene (A1C2H3) remarkably increase. Alkynes and diolefins, such as C2H2 and C3H4, have low concentrations under the experimental conditions, and their addition contributions are very low and can be ignored. Due to the addition of unsaturated species, the concentration of H2 in the gas phase is significantly improved. The modeling work can predict the coke formation characteristics and quantitatively evaluate the change in the coke formation rate, which is helpful for explaining the intrinsic thermal pyrolysis coking mechanism in a round tube, such as the regenerative cooling system of supersonic engines, among others.

Mechanical properties of saturated and unsaturated cohesive soils with stress-induced anisotropy

When anisotropic stress is applied to a soil, stress-induced anisotropy of mechanical properties develops. Using a hollow, cylindrical torsional shear apparatus, this study examined the effects of stress-induced anisotropy on the mechanical properties of saturated and unsaturated cohesive soils under different drainage conditions. Although strength anisotropy did not appear under a drained condition, it developed under undrained conditions in both saturated and unsaturated cohesive soils. The secant shear modulus exhibited a trend of becoming smaller as the angle between K consolidation and shearing became larger under both drained and undrained conditions. With regard to strength, the experimentally obtained results elucidated that the changes of excess pore water pressure and suction during shearing generated strength anisotropy. Using suction at the failure point reveals that the shear strength follows the failure criterion proposed by Fredlund and co-workers in 1978, even in a specimen with anisotropy of strength.

Analysis of constant-volume shear tests based on precise measurement of stresses in powder beds

This study demonstrates a new constant-volume shear test configuration to analyze the stresses in powder beds and evaluate powder flowability. A novel cylindrical shear cell geometry and load cell arrangement allowed precise measurement of the normal stress acting on the shear planes of the powder beds. The stress transmission ratio between the top and shear planes decreased with increasing ratio of the powder bed height in the upper section of the shear cell to the shear cell diameter. This was due to friction between the powder bed and the side wall of the upper section of the shear cell. Using the measured values of the normal stress on the shear planes, the effects of the powder bed height and shear cell diameter were eliminated from the data. In addition, to evaluate the shear properties of the powder beds, the powder yield locus, consolidation yield locus, critical state line, shear cohesion, and void fraction were obtained from a single shear test. The powder yield locus data were used to obtain flow functions.

Impact of Acoustic Radiation Force Excitation Geometry on Shear Wave Dispersion and Attenuation Estimates

Shear wave elasticity imaging (SWEI) characterizes the mechanical properties of human tissues to differentiate healthy from diseased tissue. Commercial scanners tend to reconstruct shear wave speeds for a region of interest using time-of-flight methods reporting a single shear wave speed (or elastic modulus) to the end user under the assumptions that tissue is elastic and shear wave speeds are not dependent on the frequency content of the shear waves. Human tissues, however, are known to be viscoelastic, resulting in dispersion and attenuation. Shear wave spectroscopy and spectral methods have been previously reported in the literature to quantify shear wave dispersion and attenuation, commonly making an assumption that the acoustic radiation force excitation acts as a cylindrical source with a known geometric shear wave amplitude decay. This work quantifies the bias in shear dispersion and attenuation estimates associated with making this cylindrical wave assumption when applied to shear wave sources with finite depth extents, as commonly occurs with realistic focal geometries, in elastic and viscoelastic media. Bias is quantified using analytically derived shear wave data and shear wave data generated using finite-element method models. Shear wave dispersion and attenuation bias (up to 15% for dispersion and 41% for attenuation) is greater for more tightly focused acoustic radiation force sources with smaller depths of field relative to their lateral extent (height-to-width ratios <16). Dispersion and attenuation errors associated with assuming a cylindrical geometric shear wave decay in SWEI can be appreciable and should be considered when analyzing the viscoelastic properties of tissues with acoustic radiation force source distributions with limited depths of field.

Bearing capacity analysis of helical pile foundation on peat

Peat is a kind of soil with a very low bearing capacity and high compressibility. Generally, a building construction on peat is done by using a wooden pile foundation. However, the length of the wooden piles is sometimes limited and causes the friction strength between the soil and wooden piles to became suboptimal. In order to enhance the bearing capacity of the foundation, the cross-sectional area of the foundation needs to be enlarged. One of the solutions for this problem is through helical piles. There are two methods to determine the helical pile`s bearing capacity, i.e. individual bearing and cylindrical shear methods. In this paper, bearing capacity prediction was discussed. A foundation load test was thoroughly done by a constant rate of penetration. This test consisted of compression and tension tests. The result was analyzed by individual bearing and cylindrical shear methods and next compared to each other. The result of the analysis has shown that the individual bearing method was more suitable in predicting helical piles’ bearing capacity since it produced the lowest error rate, with a magnitude of 21,31%.

EXPERIMENTAL STUDY ON DYNAMIC PROPERTIES OF STRUCTURAL SOFT CLAY BASED ON TWO KINDS OF WAVEFORM

This paper uses GCTS dynamic hollow cylindrical torsional shear apparatus and two cyclic loading waveform of sine wave and square wave. It considers the confining pressure, the influence of the vibration amplitude, frequency and the minor factors. It studies the dynamic characteristics of structural soft clay. The test results show the follows. When the dynamic stress is below the yield stress of soil structure, waveform's influence on the overall shape of the dynamic stress-strain relationship curve is very small. When dynamic stress exceeds the structure yield stress, stress-strain relationship is softening type. The softening degree of square wave is higher. Under the same conditions, square wave accumulated deformation is always greater than that of the sine wave. Waveform has an effect on pore pressure changes. The values of pore pressure under sinusoidal wave action is always greater than that of the square wave. Amplitude for the performance of pore pressure change is as follows:when the rising speed of stable amplitude is quick, the value is greater than the critical type amplitude under the action of pore pressure value. Namely the critical type amplitude under the action of pore pressure hysteresis phenomenon is serious. Yield strain and dynamic strength decrease with the increase of the vibration time trend, eventually tend to a certain value. Finally numerical size is related to the waveform. The sine wave is less than the square wave, which is contrary to the sine wave is greater than the square wave.

An Experimental Investigation of Piping Effects on the Mechanical Properties of Toyoura Sand

Piping is a complicated natural phenomenon of internal erosion, which threatens the safety of hydraulic earth structures. Despite of the comprehensive research aiming to figure out the onset condition and development of piping, there is little element experiment in laboratory regarding the mechanical properties of disturbed soil. In this paper, as an attempt to create piping erosion under controlled conditions, glucose with certain shape and volume was placed in sand samples. With the dissolution of glucose pipes, artificial piping erosion was reproduced. Based on this approach, a series of experiments were performed in a hollow cylindrical torsional shear apparatus under different confining pressures for both intact specimens and eroded ones. Strains during piping propagation were measured by local sensors. Shear modulus was obtained by conducting torsional cyclic loadings with peak to peak stress magnitude of 4 kPa under various directions of principal stress axes. Furthermore, shear strength and the development of shear band were studied. The results clearly indicate the weakened mechanical behavior of sand subjected to piping erosion. Influence of piping-induced anisotropic fabric on shear strength and shear band was also confirmed.

Effects of principal stress rotation on small strain stiffness of sand subjected to piping erosion

Along with the development of experimental techniques and numerical simulations, knowledge of the mechanism of the internal erosion process and the resulting failures has increased remarkably. Despite such advancements, little attention has been paid to the soil after erosion, whose dominant characteristic is the significant anisotropic fabric represented by discontinuities in the erosion planes. In this research, in order to investigate the small strain stiffness of eroded soil, a proposal for generating the local disturbance in the form of piping was achieved by dissolving pre-placed glucose in soil samples. A series of experiments on specimens with determined eroded planes was conducted in a hollow cylindrical torsional shear apparatus. For both the intact and the eroded specimens, the elastic shear modulus was evaluated at various stress states with the help of gap sensors under small-amplitude torsional cyclic loadings. The stress directional dependency of G was examined by changing the principal stress axes while keeping mean effective stress p′ and stress ratio σ′1/σ′3 constant. According to the results, a marked reduction in the shear modulus was induced after piping erosion, and the stiffness of the eroded soil was found to be sensitive to changes in the stress directions due to the resultant anisotropic fabric involving the loss of inter-particle contacts and the rearrangement of sand particles.

Flow-Excited Resonance of Diametral Acoustic Modes in Ducted Rectangular Cavities

The excitation of trapped diametral acoustic modes within a rectangular cavity attached to a cylindrical duct is investigated numerically and experimentally. Because the excited acoustic modes are highly three-dimensional, their interaction with the cavity shear layer results in complex patterns of flow oscillations. These are investigated for the special case of a square cavity, which exhibits three unique behaviors of the excited acoustic modes, including both stationary and spinning mode patterns. Phase-locked particle image velocimetry flow visualization accompanied with numerical simulation of the resonant sound fields indicate that the formation of disturbances is nonuniform and akin to the radial acoustic particle velocity distribution. In the instance of two acoustic modes being excited simultaneously, separate circumferential segments of the cylindrical shear layer do oscillate independently and at different frequencies, corresponding to the frequencies of the excited modes. Further, because of the symmetry inherent within the square geometry, two degenerate modes (i.e., orthogonal mode shapes with the same resonance frequency) generate a spinning mode when they are excited. The interaction of the spinning acoustic mode with the cavity shear layer leads to the formation of a three-dimensional helical vortex structure. These results underline the fact that a uniform excitation over the whole shear-layer circumference is not necessary for the generation of orderly vortical structures that maintain their coherence over the whole length of the cavity and sustain strong acoustic resonances.

Frost jacking characteristics of screw piles in seasonally frozen regions based on thermo-mechanical simulations

In this paper, a thermo-mechanical model is proposed to simulate the frost jacking behaviour of screw piles subjected to frost heave, and the results are further validated by laboratory tests. The calculated results show that large multi-helix piles yield the least frost jacking when the freezing depth reaches half the embedment depth of pile. Based on the modified cylindrical shear method and individual bearing method, the optimal geometric parameters of screw piles are determined by a series of numerical calculations. The numerical approach is expected to serve as a reference for designing effective and economical pile types in practice.

Stress-Dilatancy for Soils. Part IV: Experimental Validation for Simple Shear Conditions

Abstract This paper validates the frictional state theory using published experimental data from simple, direct and ring shear tests. Simple shear is treated as a special case of plane strain conditions. In order to define complete stress and strain, additional assumptions are made: in the direct shear and ring shear tests, simple shear is assumed to occur in the shear band. For Φo = Φ′cv = Φ′r, the stress-dilatancy relationship obtained from the frictional state theory is similar to the relationships proposed by Taylor and Bolton. Further experiments, especially those that use a hollow cylindrical shear apparatus, are necessary to fully validate the frictional state theory in simple shear conditions.

Comparison analysis of four processing methods employed in dynamic elastography to estimate viscoelastic parameters of a medium: tests using computational simulation and experiment

Dynamic ultrasound elastography is a method commonly used to quantify the mechanical parameters, such as shear elasticity modulus, and shear viscosity modulus, of biological tissues. Basically, the method employs four processing techniques, in order to estimate the mentioned parameters, denominated: phase velocity dispersion, PVD, attenuation-velocity, AV, complex shear elasticity modulus, CSM, and shear wave velocity, SV. The accuracy and precision of estimated values for and depend on the processing technique and the purpose of this paper is to compare the results obtained with PVD, AV, CSM and SV processing techniques by means of two cases: computer simulation and experiments. In the first case, the processing techniques were evaluated, via simulation, at different conditions for the signal-to-noise-ratio of the ultrasound RF echo signal used to probe the medium with vibrations due to the propagation of shear wave, the vibration amplitude and the viscoelastic properties of the medium itself. The corresponding results are expressed as the magnitudes of the mean and standard deviation of the relative error. In the second case, experiments were conducted based on a dynamic elastographic system with a cylindrical shear wave induced by a repetitive acoustic radiation force, with pulse repetition frequency of 50 Hz. A 4.98 MHz pulse-echo ultrasound system was used to probe the medium, a 3% gelatin phantom, traversed by the shear wave and the received RF echo signals were processed using the four techniques to yield the phantom values of and The results from computer simulation indicate that, in general, the CSM and AV techniques presented highest accuracy and precision. The experimental results obtained in this study are consistent with the values reported in the literature and the values of the shear elasticity modulus estimated by the four processing techniques did not differ significantly.

Nonlinear buckling and postbuckling behavior of cylindrical shear deformable nanoshells subjected to radial compression including surface free energy effects

The objective of the present investigation is to predict the nonlinear buckling and postbuckling characteristics of cylindrical shear deformable nanoshells with and without initial imperfection under hydrostatic pressure load in the presence of surface free energy effects. To this end, Gurtin-Murdoch elasticity theory is implemented into the first-order shear deformation shell theory to develop a size-dependent shell model which has an excellent capability to take surface free energy effects into account. A linear variation through the shell thickness is assumed for the normal stress component of the bulk to satisfy the equilibrium conditions on the surfaces of nanoshell. On the basis of variational approach and using von Karman-Donnell-type of kinematic nonlinearity, the non-classical governing differential equations are derived. Then a boundary layer theory of shell buckling is employed incorporating the effects of surface free energy in conjunction with nonlinear prebuckling deformations, large deflections in the postbuckling domain and initial geometric imperfection. Finally, an efficient solution methodology based on a two-stepped singular perturbation technique is put into use in order to obtain the critical buckling loads and postbuckling equilibrium paths corresponding to various geometric parameters. It is demonstrated that the surface free energy effects cause increases in both the critical buckling pressure and critical end-shortening of a nanoshell made of silicon.

A fast ray casting method for sound refraction at shear layers

The application of microphone arrays for aeroacoustic measurements in wind tunnels with an open test section requires to consider the sound refraction at the shear layer. Several methods are available for this that are either applicable to special scenarios such as planar or cylindrical thin shear layers or that require considerable computational effort. The paper concerns a new method for general application—ray casting—that is based on a ray tracing method. Ray tracing is briefly revisited and it is shown that the computational effort becomes quite high especially for large mapping grids. The ray casting approach with its interpolation technique is introduced. A time reversal technique is the key to make this approach very efficient and fast. Finally, the approach is demonstrated using two example results from simulation and from a practical measurement.