The Experts below are selected from a list of 3054 Experts worldwide ranked by ideXlab platform
Ali H. Mahfouz - One of the best experts on this subject based on the ideXlab platform.
-
Influence of initial state and Intermediate Principal Stress on undrained behavior of soft clay during pure Principal Stress rotation
Acta Geotechnica, 2018Co-Authors: Yuke Wang, Yufeng Gao, Lin Guo, Yuanqiang Cai, Ali H. MahfouzAbstract:It is important to be fully aware of the dynamic characteristics of saturated soft clays under complex loading conditions in practice. In this paper, a series of undrained tests for soft clay consolidated with different initial major Principal Stress direction ξ were conducted by a hollow cylinder apparatus (HCA). The clay samples were subjected to pure Principal Stress rotation as the magnitudes of the mean total Stress p, Intermediate Principal Stress coefficient b, and deviator Stress q were all maintained constant. The influences of Intermediate Principal Stress coefficient and initial major Principal Stress direction on the variation of strain components, generation of pore water pressure, cyclic degradation and non-coaxiality were investigated. The experimental observations indicated that the strain components of specimen were affected by both Intermediate Principal Stress coefficient and initial major Principal Stress direction. The generation of the pore water pressure was significantly influenced by Intermediate Principal Stress coefficient. However, the generation of pore water pressure was merely influenced by initial major Principal Stress direction when b = 0.5. It was also noted that the torsional Stress–strain relationships were affected by the number of cycles, and the effect of Intermediate Principal Stress coefficient and initial major Principal Stress direction on the torsional Stress–strain loops were also significant. Stiffness degradation occur under pure Principal Stress rotation. Anisotropic behavior resulting from the process of inclined consolidation have considerable effects on the strain components and non-coaxial behavior of soft clay.
Xiao-li Yang - One of the best experts on this subject based on the ideXlab platform.
-
Limit Analysis of Unsaturated Soil Slope Stability Considering Intermediate Principal Stress and Strength Nonlinearity
Geotechnical and Geological Engineering, 2017Co-Authors: Cong Yao, Xiao-li YangAbstract:Natural and man-made slopes are mostly in unsaturated soils, and the saturated or dry condition is just a particular case. This paper investigates the stability of unsaturated soil slopes. The influence of Intermediate Principal Stress is considered by introducing the unified shear strength formulation, and the strength nonlinearity of unsaturated soils is addressed by means of two different methods. Based on the upper bound theorem of limit analysis, analytical expressions of the critical height of slope are deduced. Relevant numerical solutions are obtained through optimization and parametric analysis is then conducted. It is found that: the critical height of slope increases with the increase of UST parameter b or matric suction, while it decreases with the increase of slope angles. Besides, as regards the strength nonlinearity, it’s suggested to adopt Method II when parameter \(m\) can be reasonably determined.
Jiangu Qian - One of the best experts on this subject based on the ideXlab platform.
-
influences of loading direction and Intermediate Principal Stress ratio on the initiation of strain localization in cross anisotropic sand
Acta Geotechnica, 2018Co-Authors: Xilin Lu, Maosong Huang, Jiangu QianAbstract:Since cross-anisotropic sand behaves differently when the loading direction or the Stress state changes, the influences of the loading direction and the Intermediate Principal Stress ratio (b = (σ 2 − σ 3)/(σ 1 − σ 3)) on the initiation of strain localization need study. According to the loading angle (angle between the major Principal Stress direction and the normal of bedding plane), a 3D non-coaxial non-associated elasto-plasticity hardening model was proposed by modifying Lode angle formulation of the Mohr–Coulomb yield function and the Stress–dilatancy function. By using bifurcation analysis, the model was used to predict the initiation of strain localization under plane strain and true triaxial conditions. The predictions of the plane strain tests show that the major Principal strain at the bifurcation points increases with the loading angle, while the Stress ratio decreases with the loading angle. According to the loading angle and the Intermediate Principal Stress ratio, the true triaxial tests were analyzed in three sectors. The Stress–strain behavior and the volumetric strain in each sector can be well captured by the proposed model. Strain localization occurs in most b value conditions in all three sectors except for those which are close to triaxial compression condition (b = 0). The difference between the peak shear strength corresponding to the strain localization and the ultimate shear strength corresponding to plastic limit becomes obvious when the b value is near 0.4. The influence of bifurcation on the shear strength becomes weak when the loading direction changes from perpendicular to the bedding plane to parallel. The bifurcation analysis based on the proposed model gives out major Principal strain and peak shear strength at the initiation of strain localization; the given results are consistent with experiments.
William E Vargas - One of the best experts on this subject based on the ideXlab platform.
-
effects of Principal Stress direction and Intermediate Principal Stress on undrained shear behavior of sand
Soils and Foundations, 1998Co-Authors: Mitsutoshi Yoshimine, Kenji Ishihara, William E VargasAbstract:ABSTRACT Undrained monotonic loading triaxial compression and extension tests were conducted on Toyoura sand. It was found that the shear behavior was more contractive and softer in triaxial extension than in triaxial compression. This difference suggests that the Stress conditions, such as the direction of the Principal Stress and the magnitude of the Intermediate Principal Stress have some effects on the undrained behavior of sand. To clarify these effects, a series of tests was performed by means of an automated hollow cylindrical torsional shear apparatus. Dry-deposited Toyoura sand was used in these tests. The angle of the maximum Principal Stress from the vertical to the bedding plane, α, and the Intermediate Principal Stress coefficient, b, were fixed in each test. The Intermediate Principal Stress was fixed to horizontal. For any density, tests with a larger α-value, namely, a larger inclination of σ1 from the vertical, and a larger Intermediate Principal Stress coefficient b were shown to generate greater excess pore water pressure. In addition, the undrained simple shear behavior of sand under initial isotropic and anisotropic Stress conditions was studied. It was made clear that triaxial compression (α = 0°, b = 0) gives the highest resistance with lowest contrac- tancy, while triaxial extension (α = 90°, b = 1) gives the opposite extreme in the assessment of flow failure. Simple shear mode of deformation was shown to exhibit an Intermediate Stress-strain behavior between triaxial compression and extension, which is closer to most of the field conditions.
Pathegama Gamage Ranjith - One of the best experts on this subject based on the ideXlab platform.
-
Influence of the Intermediate Principal Stress on Sandstone Failure
Rock Mechanics and Rock Engineering, 2019Co-Authors: Zhenlong Song, Guangzhi Yin, Pathegama Gamage Ranjith, Huang Jie, Chao LiuAbstract:This paper reports the results of fracture testing of sandstone under constant minor Principal Stress (20 MPa) and various Intermediate Principal Stresses. The results show that when the minor Principal Stress is constant, as the Intermediate Principal Stress increases, the ratio of the octahedral shear Stress (τoct) to the octahedral normal Stress (σoct) decreases. The strength criterion of τoct/σoct = f(σ2) is obtained. This criterion reflects not only the hydrostatic Stress and Intermediate Principal Stress effects but also the Lode angle effect. This criterion reveals the reason why the rock strength increases and then decreases with increasing Intermediate Principal Stress. The decreasing trend is fitted by linear, logarithmic and Boltzmann equations. The applicability of the three fitting equations for strength prediction and the π plane strength envelopes is analysed, and the results of the Boltzmann fitting equation are the best. The deformation characteristics of rock during the failure process are analysed. The changing process of the tangential deformation modulus of the rock is found to be divided into three stages during the loading process: an increasing stage, an initial decreasing stage and a rapidly decreasing stage. Based on an analysis of computed tomography (CT) images of the internal fractures of rock and photographs of the fracture surfaces, the internal fractures are found to be clear and smooth, and the shear Stresses in the fracture surfaces are strengthened with increasing Intermediate Principal Stress. The dominant shear Stress in the process of failure is considered to cause these phenomena.
-
Effect of Intermediate Principal Stress on the strength, deformation, and permeability of sandstone
Energies, 2018Co-Authors: Song Zhenlong, Guangzhi Yin, Pathegama Gamage Ranjith, Dongming Zhang, Chao LiuAbstract:Although the mechanical behaviors and flow aspects of sandstone have been previously investigated, studies of the effect of the Intermediate Principal Stress (σ2) on the strength, deformation, and permeability of sandstone are lacking. In this work, the mechanical behaviors and permeability of sandstone under true triaxial Stress conditions were investigated using a newly developed true triaxial geophysical apparatus. The experimental results showed that with increasing σ2, the peak strength, octahedral effective normal Stress, and octahedral effective shear Stress of the sandstone increased, and the rate of increase decreased. This is because a larger Intermediate Principal Stress coefficient b has an inhibitory effect on rock strength. In our study, as the ratio of σ2/σ3 increased, the specimen entered compressive strain in the σ2 direction during the first Stress drop. The Stress and strain path deviations occur during rock failure. The amount of deviation increased as the σ2 increased before the peak Stress. This phenomenon indicates that elastic mechanics are not suitable for understanding this sandstone rock during its failure. The permeability evolution of the sandstone under true triaxial Stress conditions was measured and analyzed to investigate the effect of σ2. During the complete true triaxial Stress-strain experiments, the variation we found in gas seepage velocity could be divided into two stages. Before the first pressure drop, the gas seepage velocity was mainly affected by volume strain. After the first pressure drop, the seepage velocity was affected by the deviator strain, which can change the seepage channels.
-
Failure Characteristics of Granite Influenced by Sample Height-to-Width Ratios and Intermediate Principal Stress Under True-Triaxial Unloading Conditions
Rock Mechanics and Rock Engineering, 2018Co-Authors: Fan Feng, Pathegama Gamage Ranjith, Jamal RostamiAbstract:The failure modes and peak unloading strength of a typical hard rock, Miluo granite, with particular attention to the sample height-to-width ratio (between 2 and 0.5), and the Intermediate Principal Stress was investigated using a true-triaxial test system. The experimental results indicate that both sample height-to-width ratios and Intermediate Principal Stress have an impact on the failure modes, peak strength and severity of rockburst in hard rock under true-triaxial unloading conditions. For longer rectangular specimens, the transition of failure mode from shear to slabbing requires higher Intermediate Principal Stress. With the decrease in sample height-to-width ratios, slabbing failure is more likely to occur under the condition of lower Intermediate Principal Stress. For same Intermediate Principal Stress, the peak unloading strength monotonically increases with the decrease in sample height-to-width. However, the peak unloading strength as functions of Intermediate Principal Stress for different types of rock samples (with sample height-to-width ratio of 2, 1 and 0.5) all present the pattern of initial increase, followed by a subsequent decrease. The curves fitted to octahedral shear Stress as a function of mean effective Stress also validate the applicability of the Mogi–Coulomb failure criterion for all considered rock sizes under true-triaxial unloading conditions, and the corresponding cohesion C and internal friction angle φ are calculated. The severity of strainburst of granite depends on the sample height-to-width ratios and Intermediate Principal Stress. Therefore, different supporting strategies are recommended in deep tunneling projects and mining activities. Moreover, the comparison of test results of different σ2/σ3 also reveals the little influence of minimum Principal Stress on failure characteristics of granite during the true-triaxial unloading process.
