Gotowa bibliografia na temat „Hollow Cylinder Trosional Shear Tests”

This paper presents the method to obtain the shear stress curve of clay from the undrained plane-strain expansion of hollow cylinder triaxial tests. No prior knowledge of the constitutive properties of the material is required. The theory also indicates that when the outer radius of the cylinder is very large compared with the inner radius, the equation used to interpret pressuremeter tests in clay is recovered.Key words: hollow cylinder, expansion tests, clays, plane strain, undrained condition, shear stress curve.

Abstract The paper presents the results of tests performed in a Torsional Shear Hollow Cylinder Apparatus on undisturbed cohesive soils. The tests were performed on lightly overconsolidated clay (Cl) and sandy silty clay (sasiCl). The main objective of the tests was to determine the undrained shear strength at different angles of rotation of the principal stress directions. The results of laboratory tests allow assessing the influence of rotation of the principal stress directions on the value of undrained shear strength that should be used during designing structure foundations

Shear banding in Santa Monica beach sand deposited by dry pluviation in hollow cylinder specimens is studied in 34 drained torsion shear tests with rotation of principal stress directions. The effect of the specimen height on the soil behavior was investigated by testing specimens with heights of 40 and 25 cm. Each test was conducted with the same, constant inside and outside confining pressure, σr, thus tying the value of b = (σ2– σ3)/(σ1 – σ3) to the inclination, β, of the major principal stress. Shear bands can develop freely without significant restraint from the soft rubber membranes. Strain localization and shear banding were observed in the hollow cylinder specimens, and this created failure conditions in plane strain and in tests with higher b-values. The results clearly indicate the influence of the cross-anisotropic fabric on the stress–strain behavior, on the shear band inclination, and on the shape of the failure surface.

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.

Described are failure tests performed on a fine-grained Leighton Buzzard sand in the Nottingham hollow cylinder apparatus. These tests were conducted to characterize the inherent anisotropy of the material formed during the sample preparation procedure. An image analysis procedure for determining preferred particle orientation is introduced and its derivation discussed. An attempt is subsequently made to relate the statistically significant preferred orientation to the anisotropic shear strength properties of the Leighton Buzzard sand.

A new hollow cylinder torsional shear apparatus is described. The apparatus is suitable for investigating soil behaviour under generalized stress paths, including principal stress rotations, characteristic of earthquake and offshore-wave loadings. A new, more rational assessment of stress nonuniformity across the wall of the hollow cylinder specimen is made, and the "no go" regions of the stress space are delineated that limit stress nonuniformity to acceptable levels. Operation of the apparatus and experimental procedures for tests on reconstituted specimens of sand are described. Typical results of drained tests on loose and dense sand are presented to illustrate the capabilities of the apparatus as a general stress-path loading device and to highlight the stress-path dependence of soil behaviour, in particular, the deformation response to principal stress rotations. Key words: hollow cylinder apparatus, generalized stress paths, principal stress rotation, sand, deformations.

The measurement and study of the stress–strain–strength behaviour of soils in general stress states involving the change of magnitudes and direction of the principal stresses are necessary and important. To investigate the strength behaviour under such conditions, consolidated undrained tests on remoulded hollow cylinder specimens of completely decomposed granite (CDG) were carried out using a hollow cylinder apparatus. Tests were conducted by maintaining a fixed principal stress direction with angle α from the vertical direction together with a fixed value of intermediate principal stress coefficient b. It is observed that the value of the friction angle decreases with an increase in α and the failure surface is anisotropic. There is an increase in friction angle with an increase in b value up to b = 0.25, and the friction angles are almost the same for b > 0.25. In addition, the behaviour of the soil in an undrained simple shear condition was examined. The simple shear condition is very near to the condition of α = 45° and b = 0.25. After having analyzed the test results of all hollow cylinder specimens, it was found that the strength anisotropy is very strong and is dependent on the principal stress direction and intermediate principal stress coefficient.

Direct measurements of the initial shear strength and yielding anisotropy of a dense, K0-consolidated silt are described and interpreted within a bounding-surface framework. The experiments were performed using the Imperial College large hollow cylinder apparatus, in which samples were sheared undrained with a range of orientations, α, of the major principal stress, σ1, following initial K0 consolidation. The interpretation is aided by data from oedometer and triaxial stress path tests. Strongly anisotropic stiffness, yielding, undrained strength, and mobilized angle of shearing resistance, ϕ', characteristics are revealed. The effects of drained and undrained stress changes applied to the samples after K0 consolidation are also described.Key words: anisotropy, hollow cylinder, K0 consolidation, silt, bounding surface.

In this paper the behaviour of two “standard research sands”, widely used for experimental purposes, is compared in a torsional hollow cylinder apparatus under monotonic and cyclic loading conditions. Both sands are fine and uniform with D50 = 0.22 and 0.29 mm, respectively. However, their response to undrained monotonic loading at similar void ratios is dramatically different, with the finer sand showing strength reduction after peak and the coarser sand showing continuous increase in strength with torsional shear. The difference in response is mainly attributed to grain angularity and to a lesser degree to their grading. The results of drained torsional hollow cylinder tests show initial contraction followed by dilation. The stress ratio at phase transformation is uniquely defined by both drained and undrained tests for each sand. Cyclic loading instability is manifested by a sudden increase in shear strain and excess pore-water pressure leading to initial liquefaction. The instability initiates across the instability line for the sand showing strength reduction and across the phase transformation line for the sand showing continuous increase in strength with shearing. Both lines are defined under monotonic loading conditions. The liquefaction, stiffness, and damping characteristics of the sands are given in this paper.

Cemented granular systems are encountered at various scales in nature and artificially. We present an experimental study carried out on the structure and mechanical behaviour of weakly cemented granular materials. We study the cemented granular materials at two scales -- micro (particle-bond-particle) scale and macro (ensemble) scale. At the micro-scale studies, a set of x-ray computed tomography experiments are performed. We characterize the structure of initial configuration of weakly cemented granular materials. We discuss, in detail, quantification of fabric and structure such as coordination number, fabric tensor, directional distribution of contact normal and particles, and grain size distribution. An alternative approach to arrive at the fabric tensor is also discussed. To obtain these characteristics, the scanned volume from XCT is segmented into particles and contacts (bonds - for a contact bound structure). For the segmentation, watershed along with h-minima or h-maxima transform are used. The algorithm is presented in detail for a two dimensional example image. From the segmentation results, it is observed that the particles of cemented granular materials orient themselves away from the direction of the gravity or body force whereas the contact normals have a tendency to orient along the direction of gravity. Further, we perform a set of uni-axial compression tests inside the X-ray computed tomograph. It is observed that the initial structure of cemented granular material does not changes significantly before the peak load is reached. The average coordination number increases at lower strains due to contraction of the specimen however at larger strains, continuous reduction in coordination number is observed. The evolution of average porosity field has similar trend to the volumetric strain. Further, the particle and contact align themselves along the direction of load at lower strains whereas at higher strains, they orient themselves away from the loading direction. At macro-scale, we perform a set of triaxial and hollow cylinder shear tests to understand the effect of confining pressure, intermediate principal stress ratio, and density on weakly cemented sands. These results are analyzed in the framework of plasticity theory. We present the extraction of gross yield points of bonds, plastic work contours or yield curves, plastic strain increments, and failure. Further, we calibrate and validate the Lade's single hardening elastic-plastic model. The details of model parameter calibration and integration algorithms for prediction of behaviour are provided. The Lade's model uses stress transformation for accommodation of cementation in the model. Stress transformation implies the translation of elastic-plastic surface along the hydrostatic axis in the stress-space by bond strength of cemented sands. With this stress transformation, the stress-strain response is predicted satisfactorily however, the volumetric predictions only show contraction. In contrast, the experimental volumetric behaviour is initially contractive followed by a dilative response (in the range of confining pressure tested). To validate the applicability of stress transformation, we perform a set of experiments with cemented sands and sands (equivalent sand) subjected to elevated confining pressure (increased by the bond strength). The response suggest that the stress transformation is satisfactory at small strain however due to bond breakage, a deviation in the cemented sands and equivalent sand is observed. This behaviour suggest that the inclusion of bond degradation with stress transformation should work successfully. To verify this, we include the bond degradation in the stress-dilatancy relation for prediction of stress-dilatancy behaviour of cemented sands. With inclusion of bond degradation, the Rowe's and Zhang-Salgado's stress dilatancy relation successfully predict the stress-dilatancy behaviour of cemented sands. We provide microstructural insights from our tomography experiments to the macro level response observed under various stress conditios. Further, a set of scaling studies are also performed on unconfined compressive strength with varying particle sizes (particle size effect), specimen sizes (specimen size effect), and controlled study (scaling specimen and particle sizes proportionally to keep number of particles fixed). With increase in the specimen size, the peak compressive strength of weakly cemented granular material increases. The peak compressive strength decreases with increase in the size of particle. In controlled study, the strength is insensitive to proportional scaling of specimen and particles. The scaling in these contact bound granular materials is significantly different from brittle and quasi-brittle solids such as rocks and concrete. To understand the emergence of the scaling, we use microstructural characteristics obtained from XCT. In particular, we obtain the geometric clusters which are akin to force chains i.e. geometric clusters are able to predict the force distribution in a granular material from its structure. Using the percolation probability of these geometric cluster and normalized cluster size, similar trends as strength are obtained. The primary source of these scaling is results of entanglement of force chains which is presented here by entanglement of geometric cluster.
Department of Science and Technology

碩士
國立交通大學
土木工程系所
93
The concept of using local displacement measurement for soil element testing has been well accepted by the international geotechnical engineering community. The available techniques however, are mostly developed for monitoring linear displacement such as the axial deformation in a triaxial test. Methods to provide local rotational displacement measurement in a hollow cylinder torsional simple shear test are rare. The main objective of this research is to develop a practical method to monitor the specimen rotational displacement locally, in a hollow cylinder torsional simple shear test. Coupled with beneder elelment, the new technique was used in a series of cyclic tests on a silty sand with various fines contents. The effects of fines contents on the correlations among shear modulus, damping ratio, pore pressure development and shear strain were then studied based on these tests.

博士
國立成功大學
土木工程學系碩博士班
100
Conventional test has a lot of limitations. The effect of complex three-dimensional stress on rock cannot be simulated by triaxial test; and the true residual shear strength at rock joint surface cannot be obtained by direct shear test. Therefore, suitable methods and equipments for hollow cylinder triaxial test and ring shear test for rock specimen are developed in this study to obtain the failure criteria of rocks in three-dimensional stress and residual state. Hollow cylinder triaxial test is applied to the cover and storage layers in CO2 sequestration to probe the strength properties under three-dimensional stress and establish three-dimensional yield surfaces. The results show that the yield surfaces of Yutengping sandstone, Liuchungsi sandstone and Kanhsialiao mudstone appear as smoothed triangle on octahedral plane, indicating a nonlinear relationship between the deviator stress and angle of deviation at the moment of failure. In failure criteria analysis, both Hoek-Brown and Kim-Lade failure criteria could present the strength properties of rocks under low and high confining pressure. However, Kim-Lade failure criterion could also express the influence of the angle of deviation to deviator stress, and its yield surface (which is a smoothed triangle) is more similar to test results. The yield surface could then be used to assess the maximum allowable injection pressure of storage layer under three-dimensional stress as the reference value for injection pressure in CO2 sequestration to reduce the risk of rock failure. In addition to using ring shear test to probe the residual strength at rock joint surface, it is also used to simulate the effect of seismic forces on rock sliding surface to probe the sliding mechanism by the application of dynamic stresses. Test results show that the failure criterion established in static ring shear test is applicable in dynamic test. As the dynamic forces surpasses the shear resistance of sliding surface, shear path moves along failure envelope. At this moment, shear displacement increases rapidly to a maximum rate of 5.12m/min, which is enough to cause sliding failure on rock slope. This phenomenon explains the mechanism of Tsaoling landslide which was caused by Chi-Chi earthquake, which was happening when the dynamic (seismic) stresses on the sliding surface surpassed the resisting shear strength, resulted in a high-speed sliding. As the conclusion, the hollow cylinder triaxial test and ring shear test developed in this research could overcome the limitation faced in conventional methods, to probe the strength properties of rock under three-dimensional stress and residual state, and provide a great help in solving current rock mechanics problems.