Consolidation Of Specimens Research Articles

Influence of shear rate on the soil's shear strength

One of the most important mechanical properties is shear strength. It is conditioned by the value of the maximum shear stress that the soil can withstand before failure. Exceeding the shear strength causes one particle to slide next to another, causing the failure of soil. The shear strength of the soil for effective stresses is1 a combination of drained strength parameters: internal friction angle (φ) and cohesion (c) defined by the Mohr-Coulomb failure criterion. It is determined “in situ” and by laboratory experiments. Direct shear is the oldest and the simplest laboratory experiment to determine the shear strength of the soil. The first phase of experiment is specimen consolidation under specific vertical stress, and in the second phase specimens are sheared at a given shear rate, depending on the consolidation properties of the soil. Cohesionless soils are sheared at up to 100 times higher shear rate compared to cohesive soils. Shear rate and drainage conditions affect the magnitude of soil strength parameters. The paper is based on the comparison and demonstration of the influence of different shear rates on the peak and residual shear strength in the direct shear device. The tests were performed on two samples of low plasticity clay (CL) and one sample of high plasticity clay (CH).

Designing a diagnostic Total Testing Process as a base for supporting diagnostic stewardship.

To more comprehensively support clinical management of patients in our hospital, we redesigned the diagnostic Total Testing Process (TTP) from request to report. To that end, clinical needs were identified and a vision on Total Laboratory Automation (TLA) of the TTP was developed. The Delft Systems Engineering Approach was used for mapping a desirable laboratory testing process. The desirable "To Be" diagnostic process was tendered and the translation of a functional design into a specific TLA-configuration- compliant with the vision andthe predefined functional design- was accomplished using a competitive dialogue tender variant (based on art. 29 of the EU guideline 2014/24). Realization of this high-end TLA-solution enabled a high-quality testing process with numerous improvements such as clear and supportive digital request forms, specimen consolidation, track and trace and non-conformity registration at the specimen level, better blood management (∼40% less blood sampled), lean and in line processing with increased productivity (42% rise in test productivity per capita), and guaranteed total turn-around-times of medical tests (95% of TLA-rooted in line tests are reported<120min). The approach taken for improving the brain-to-brain loop of medical testing, as fundament for better diagnostic stewardship, is explained.

A note on falling-head and rising-tail permeability tests on saturated soils in centrifuge

The falling-head and rising-tail method for permeability test allows for both inflow and outflow rates to be conveniently measured. This helps to detect any possible swelling or consolidation of specimen during testing and to identify the continuity of flow of water through the specimen. It has been widely adopted to measure the hydraulic conductivity of saturated porous media of extremely low permeability, such as hydraulic barrier soil materials. Centrifuge permeameter test with this method has recently been devised to accelerate water flow and reduce the time needed for testing. The accompanying equation for calculating hydraulic conductivity is, however, found to be simplified because it was formulated by idealizing such a variable-head test as multiple segmental constant-head tests. In this paper, a new generalized equation is established based strictly on the variable head. Moreover, based on curve matching between the rates of flow into and out of the soil specimen, an approach is also proposed to identify the continuity state of flow. The data relevant to this state are extracted for performing the calculation of hydraulic conductivity. The practical application of the proposed equation and its associated approach is illustrated through a reanalysis of recently published experimental data in the literature.

Stress dependence of elastic P-wave velocity and amplitude in coal specimens under varied loading conditions

Experiments allowed finding regular patterns in propagation of elastic P-waves in specimens of black coal exposed to uniaxial compression and triaxial compression by von Karman. It is shown that in case of uniaxial compression, the largest information content is ensured by translucence in perpendicular to bedding and loading axis of coal specimens. Such translucence exhibits four stages of deformation of a specimen. The information content of translucence under triaxial compression reduces with the increase in the constrained pressure that prevents from disintegration of a coal specimen. Four deformation stages are best identified with the constrained pressure of 2.5 MPa, while only stages of specimen consolidation and failure are traced at the pressure of 10 MPa.

Triaxial tests on undisturbed gravelly soils from the Sicilian shore of the Messina Strait

The paper reports the results of laboratory testing of dense sandy gravel carried out on large dimension undisturbed samples, obtained by means of in situ freezing technique. The specimens, 290 mm in diameter and 600 mm high, have been subjected to undrained cyclic triaxial tests carried out in isotropically and anisotropically consolidated conditions aimed at investigating sandy gravel susceptibility to cyclic mobility and plastic strain accumulation during earthquake induced vibrations. The quality of the undisturbed samples was corroborated by comparing the field shear wave velocities against those inferred from bender element tests, carried out in the triaxial apparatus after the specimen consolidation. The cyclic tests were supported by a series of monotonic undrained and drained triaxial tests performed on isotropically and anisotropically consolidated specimens to help in their more rational interpretation. The tests yielded valuable information as to the susceptibility of the sandy gravel in hands to cyclic mobility and plastic strain accumulation during earthquake loading.

Numerical Simulation of Consolidation Test Considering Different Drainage Height

Numerical simulation of the consolidation test was developed in different drainage conditions using the finite difference method. Soil sample was divided into layers to determine the time-steps of the test. A series of simulation tests were carried out to study the influence of drainage height on the coefficient ratio. Finally, some experiments data were compared with the numerical simulation results. Numerical results indicate that the simulation method broke through the limitation of test apparatus, and made it possible to conduct big size specimen consolidation test under certain conditions.

Hard Alloy WC–24% Ni Obtained in the Solid Phase from Ultrafine WC, NiO, and C Powders. Part 2. Mechanical Properties

Mechanical properties of WC–24 mass% Ni alloy prepared by a combination in single stage of metal phase synthesis and compaction of an ultrafine mixture of WC–Ni powders by high-energy compaction and sintering are studied. Tungsten carbide, nickel oxide, and carbon are selected as the starting powders. After milling the initial powders the average particle size is 200-300 nm. Previously compacted briquettes of WC + NiO + C are heated, sintered, and pressed in the range 950-1300°C at vacuum of 0.133 Pa. Briquettes are also sintered in the liquid phase at 1350°C for comparison. Ultimate strength in bending, fracture toughness, ultimate strength in compression, and Vickers hardness are determined for specimens prepared at different temperatures. The dependence of mechanical properties on specimen consolidation temperature is studied. It is shown that these dependences for pressed specimens have a maximum at 1200-1250°C. The high level of properties (ultimate strength in bending 2500 MPa, ultimate strength in compression 3100 MPa, fracture toughness 19 MPa·m1/2, and hardness 10.0 GPa) are achieved for a WC + Ni + C powder mixture to which carbon is added in the form of a liquid carbon-containing compound. Introduction into the mixture of commercial carbon grade P803 leads to low specimen mechanical properties. The effect on mechanical properties of porosity and pore size, and also grain boundary quality between particles is studied.

Effects of specimen consolidation on the laboratory hydraulic conductivity measurement

Laboratory hydraulic conductivity tests are commonly used for the design of clayey liners in waste containment. Although relatively small hydraulic gradients are encountered under field conditions, elevated gradients are desirable to reduce the testing time. It is generally believed, however, that these elevated gradients would reduce the conductivity measured owing to specimen consolidation. In the current paper a theoretical analysis is presented for assessing the effect of specimen consolidation. The theoretical results were compared with experimental results obtained for two local soils. Parametric analyses and nondimensional analyses were carried out and the results are presented. It was found that the hydraulic conductivity is dependent on the type of permeameter, the form of gradient application, and the state of stress within the soil. It was apparent that hydraulic conductivity can decrease with an increase in the hydraulic gradient, and the decrease was not significant up to a hydraulic gradient of about 300 for the soils tested.Key words: hydraulic conductivity, hydraulic gradient, specimen consolidation, volume change, permeameter.

A Modified Commercial Triaxial Testing System for Small Strain Measurements: Preliminary Results on Pisa Clay

Abstract A computer-controlled hydraulic triaxial cell was modified with the aim of obtaining (1) a better measuring accuracy of soil stiffness at small strains, (2) a reliable automatic procedure for K0 consolidation, and (3) a minimum disturbance during system saturation and specimen consolidation. To obtain the above objectives, many modifications were introduced. The cell structure and loading piston were modified and many transducers were introduced, including the LDTs for local radial and axial strain measurement. Finally, control software was developed to achieve the following testing procedures: (1) dry setting, (2) system saturation by flushing with stress control to avoid any swelling and back pressurization, and (3) K0 consolidation with control of nil radial strain by means of local measurement. The paper will benefit those interested in upgrading an existing hydraulic triaxial system in-house in an economical manner.

Bearing behavior of triaxially braided flat and tubular composites

An experimental study was carried out to evaluate the bearing behavior of glass fiber reinforced epoxy composites made from the triaxial braiding process. The bearing strengths of braided and machined holes in flat as well as tubular samples were compared. The effects of specimen geometry, braid angle, and specimen consolidation condition were investigated. Comparison between specimens with braided and machined holes indicated a higher bearing capacity for the braided joint hole compared with the machined one in tubular specimens whose thickness was not precisely controlled. For flat samples with uniform thickness, the braided hole showed similar or even lower bearing capacity compared with the machined hole, possibly due to the disturbance in fiber arrangement around the braided hole.

SINTERING AND SYNTHESIS OF THE PSEUDOBROOKITE OXIDE (Fe2TiO5) BY THE SOLID STATE REACTION

Pseudobrookite oxide Fe 2 TiO 5 was synthesized by the solid state reaction. Synthetic pseudobrookite (Fe 2 TiO 5 ) was prepared form high purity hematite (Fe 2 O 3 ) and rutile (TiO 2 ) through conventional powder processing methods. This paper reports a synthetic way to yields a fine pseudobrookite powder suitable for specimen consolidation and sintering

Physical isomorphism in the mechanical behaviour of soils

The validity of Buckingham's theorem for a group of soils indicates that the behaviour complies with the condition of physical similitude. Buckingham's dimensionless arguments can be generalized using the conception of dimensionless "criterial" functions, of stress-strain diagram for example; behaviour in harmony with these functions is called physically isomorphous behaviour.By analysing some experimental findings, the author shows that typical for isomorphous behaviour are logarithmic curves (e.g., curve of compression or primary creep) and linear Mohr's envelopes.Two deformation mechanisms are discriminated, that of sliding deformation and that of cataclastic deformation. Only the domination of the first one produces physical isomorphism. Microrheological analysis shows, in a rather qualitative way, that physical isomorphism results from the monotonous strain, stress, and time hardening of the structure of the soils in question. Such structural changes are typical for soft to medium clays and loose sands and for many soils in the range of high pressures. These soils manifest, consequently, physically isomorphous behaviour.The importance of the principle of physical isomorphism is illustrated by its application to creep (Saito–Uezawa relation), to primary consolidation of specimens with varying drainage paths, and to the interpretation of the ratio Ccε/Cαε of compression index to secondary compression index. Key words: model laws, soil structure, compression, creep, shear strength.