The Experts below are selected from a list of 291 Experts worldwide ranked by ideXlab platform
Paul R Young - One of the best experts on this subject based on the ideXlab platform.
-
numerical investigation of the mechanical and damage behaviors of veined gneiss during true triaxial Stress Path loading by simulation of in situ conditions
Rock Mechanics and Rock Engineering, 2020Co-Authors: Paul R YoungAbstract:Investigations on the Posiva Olkiluoto spalling experiment (POSE) at the nuclear waste disposal site in Olkiluoto, western Finland, have revealed that the presence of anisotropic veined gneiss (VGN) could affect the evaluation of spalling/damage strength of the host rock. In this study, the mechanical and damage behaviors of anisotropic VGN during complex true-triaxial in situ Stress Path loading is numerically investigated, considering the lifetime Stress evolution of POSE. Overall, the discrete element numerical results show reasonable agreement with those of laboratory experiments for both strength and damage development. Numerical simulations at the microscale showed that the damage is concentrated within the discontinuous foliation bands and at the interfaces between weak and strong bonds when the mineral composition of the foliation bands is heterogeneous. It is possible that the varying stiffnesses of the two materials cause strain concentration at strong segments within the weak foliation bands or high strain gradients at the interfaces between the weak and strong bands, leading to tensile failure of the strong bonds. However, if continuous foliation bonds are employed, fractures mainly propagate within the weak bonds, indicating that the heterogeneity of the foliation bonds is a predominant factor affecting the failure of VGN. After weak bonds and interfaces failure, shear movements occur along the weak bonds, forcing the strong bonds to bear most of the load. The simulations also show that the unloading of σ2 and σ3 triggers microcracks in the early stages, revealing the role of unloading in rock damage. The change in the secant modulus in relation to the foliation angle is generally found to follow a U-shaped anisotropy and obtains the lowest value at 45°. For each test, the modulus gets the minimum value in the damage stage and recovers in the unloading stage, but it cannot reach its original value. Sample strength increases as the foliation orientation angle increases from 0° to 45° in relation to σ2, because the increase in normal Stress from σ2 causes the role of the strong foliation bonds to become significant as the bonds strengthen. The damage to the strong bonds leads to a larger reduction in the modulus at the damage stage.
-
true triaxial experimental investigation of rock response around the mine by tunnel under an in situ 3d Stress Path
Rock Mechanics and Rock Engineering, 2019Co-Authors: Maria Tibbo, M H B Nasseri, Paul R YoungAbstract:Underground excavation causes rock damage, affecting its stability and fluid transport properties. Traditional experiments usually use loading regime (compressive tests) to damage the sample. However, they cannot mimic realistic in situ conditions where excavation unloading also plays a significant role. In the study, we conducted a true-triaxial acoustic emission (AE) experiment to simulate excavation-induced damage by applying in situ 3D Stress Path to a sample. The Path originating 1.0 cm from the Mine-by tunnel crown at the Underground Research laboratory (URL) was determined using an elastic numerical model as the tunnel advanced. The computed Stress Path was applied to a cubic granite sample using a state-of-art true-triaxial facility to simulate rock damage in the roof. AE activity was intensively monitored, and a damaged plane was determined by fitting a plane through the localized AE events. A source parameter analysis for cluster events near the damaged plane was undertaken via a spectral fitting method. The source type was determined using the moment tensor inversion method. The source size and Stress drop were also estimated. The results indicated that Stress unloading plays an important role in AE activity. Temporal characteristics of AE events were converted to a spatial distribution relative to the tunnel advancement; this exhibited a good agreement with the microseismicity recorded in the tunnel roof. Source parameters (e.g., corner frequency and moment magnitude) were consistent with the field recordings. Stress drop of the experimental events ranged from 0.6 to 6 MPa, which was comparable with the higher seismicity recorded at the Mine-by tunnel roof. The Stress rotation and low confinement that may cause disagreement between the laboratory and field observations are critically analyzed.
Jeanmarie Konrad - One of the best experts on this subject based on the ideXlab platform.
-
a unified constitutive model for simulating Stress Path dependency of sandy and gravelly soil structure interfaces
International Journal of Non-linear Mechanics, 2018Co-Authors: Miad Saberi, Charlesdarwin Annan, Jeanmarie KonradAbstract:Abstract A plasticity constitutive model is proposed to simulate the monotonic and cyclic behavior of granular soil–structure interfaces. The model is built on two-surface plasticity models previously developed for interfaces between gravelly soils and structural materials (Saberi et al., 2016, 2017), which simulate strain hardening, Stress degradation and phase transformation behavior. The proposed model in this study incorporates the softening behavior likely to occur in dense sandy soil–structure interfaces under monotonic and cyclic loading, and it provides a unified formulation for simulating the behavior of both sandy and gravelly soil–structure interfaces. The model accounts for the Stress Path dependency behavior of interfaces, and it requires a single set of nine calibration parameters, which can readily be obtained from standard interface shear tests. The interface model’s performance is evaluated for Constant Normal Load, Constant Normal Stiffness, and Constant Normal Height Stress Path conditions by comparing its predictions with experimental data.
Sai K. Vanapalli - One of the best experts on this subject based on the ideXlab platform.
-
Stress-Path dependent behavior of a weathered clay crust
Geotechnical & Geological Engineering, 2006Co-Authors: Vinod K. Garga, Mahbubul A. Khan, Sai K. VanapalliAbstract:Triaxial compression and oedometer consolidation tests are commonly performed to evaluate the strength and deformation behavior of soils. However, in the field, the Stress Paths imposed by various engineering works may deviate from the Stress Paths conventionally used in laboratory tests. Moreover, the Stress-Paths followed by different soil elements under a foundation are different. To obtain representative soil parameters, the laboratory Stress Path should be similar to that followed in the field. In this study, a significant number of Stress-Path triaxial tests, with Stress probes in various directions, have been conducted to study the Stress-Path dependent behavior of an overconsolidated weathered crust of Champlain clay in Eastern Ontario. Both undrained and drained tests have been conducted for samples isotropically consolidated to the in situ vertical Stress and anisotropically consolidated to in situ state of Stress. The yield locus of the clay crust has been defined. It has been observed that the strength-deformation and yielding behavior of this weathered clay crust highly depends on the Stress-Path as well as on the in situ Stress history.
Jinfeng Chen - One of the best experts on this subject based on the ideXlab platform.
-
a large triaxial investigation of the Stress Path dependent behavior of compacted rockfill
Acta Geotechnica, 2012Co-Authors: Ming Xu, Erxiang Song, Jinfeng ChenAbstract:Realistic prediction of the deformation of rockfill structures becomes increasingly important, which requires improved knowledge about the mechanical properties of rockfill materials. However, previous large triaxial tests were usually carried out with a constant cell pressure, and there is uncertainty about the behavior of rockfill along other Stress Paths. This paper presents the results of a series of large triaxial tests conducted on limestone rockfill specimens along different loading Paths. The effect of previous loading history and moisture content has also been investigated. The results show that the Stress–strain and volumetric behavior of rockfill are significantly influenced by the loading directions as well as the confining pressures. However, the Stress Path appears to have only minor influence on the shear strength of rockfill, while the strength envelope exhibits pronounced curvature at low confining pressures and the peak friction angle decreases approximately linearly with the logarithm of the corresponding confining pressure. The previous loading history is revealed to have considerable effect on the Stress–strain behavior but small influence on the peak strength of rockfill. In contrast, the moisture content of rockfill has marked influence on both the deformation and the strength characteristics. The implications of the test results are discussed.
Miad Saberi - One of the best experts on this subject based on the ideXlab platform.
-
a unified constitutive model for simulating Stress Path dependency of sandy and gravelly soil structure interfaces
International Journal of Non-linear Mechanics, 2018Co-Authors: Miad Saberi, Charlesdarwin Annan, Jeanmarie KonradAbstract:Abstract A plasticity constitutive model is proposed to simulate the monotonic and cyclic behavior of granular soil–structure interfaces. The model is built on two-surface plasticity models previously developed for interfaces between gravelly soils and structural materials (Saberi et al., 2016, 2017), which simulate strain hardening, Stress degradation and phase transformation behavior. The proposed model in this study incorporates the softening behavior likely to occur in dense sandy soil–structure interfaces under monotonic and cyclic loading, and it provides a unified formulation for simulating the behavior of both sandy and gravelly soil–structure interfaces. The model accounts for the Stress Path dependency behavior of interfaces, and it requires a single set of nine calibration parameters, which can readily be obtained from standard interface shear tests. The interface model’s performance is evaluated for Constant Normal Load, Constant Normal Stiffness, and Constant Normal Height Stress Path conditions by comparing its predictions with experimental data.
