This paper describes the influence of joint spacing and joint orientation on the penetration rate of a Tunnel Boring Machine （TBM） disc cutter as modeled by the Discrete Element Method （DEM）. The input data for th...This paper describes the influence of joint spacing and joint orientation on the penetration rate of a Tunnel Boring Machine （TBM） disc cutter as modeled by the Discrete Element Method （DEM）. The input data for the siLmulations were obtained from the sandstone along the AIborz tunnel that is currently being excavated in Iran using a 5.2 m diameter open TBM. Three joint spacings, 150, 200, and 300 mm, were modeled together with seven values of joint orientation; 0°, 15°, 30°, 45°, 60°, 75°, and 90°. The results show that the penetration increases when joint orientation increases from 0° to 75°, but it decreases as the joint orientation increases further from 75° to 90°. This is true for each joint spacing. In addition, for a given joint orientation increasing the joint spacing causes the TBM penetration to decrease. The optimum joint orientation, from the viewpoint of TBM penetration, is about 60-75°.展开更多
Objective:To examine the relationship between changes in lumbar spine facet joint(FJ)orientation and chronic low back pain(CLBP).Methods:We retrospectively analyzed lumbar spine CT and MRI images of 98 patients referr...Objective:To examine the relationship between changes in lumbar spine facet joint(FJ)orientation and chronic low back pain(CLBP).Methods:We retrospectively analyzed lumbar spine CT and MRI images of 98 patients referred for localized paraspinal CLBP and 98 age-and sex-matched asymptomatic individuals as controls.They were divided into four age groups(A,<40;B,41-50;C,51-60;D,61-70;and E,71-80 years old,respectively).FJ orientations were evaluated at the L3-4,L4-5,and L5-S1 lumbar levels.Results:FJ angle showed a statistically significant more sagittal orientation in CLBP patients than in control groups in lower lumbar spine segments.The overall mean FJ angles in CLBP groups including all age groups combined at L3-4,L4-5,and L5-S1 levels were 32.33±4.5,36.11±2.9,and 37.4±6.1,degrees,respectively.The FJ angles in control group for all ages were 32.21±3.7,38.01±4.6,and 40.18±6.8°,respectively.The differences in FJ angle were statistically significant at both L4-5 and L5-S1 levels between the control and the CLBP groups(p<0.01).The FJ orientation from upper lumbar spine to lumbar sacral junction demonstrated a gradual more coronal orientation transition in all subjects but this trend was significantly less in CLBP patients.The mean FJ angles for the control group at age groups A,B,C,D,and E were 33.52±3.8,35.7±4.5,38.25±2.4,35.49±4.1,and 38.13±5.8,respectively,while those in the CLBP groups were 35.63±2.4,35.26±3.6,35.99±5.1,35.3±4.3,and 35.17±6.7,respectively.Conclusion:There is a significant association between a more sagittal FJ orientation and facetogenic CLBP in lower lumbar vertebral levels.There is also age-dependent decrease in FJ orientation in sagittal plane at lower lumbar spinal levels in control as well as CLBP groups,however,this decrease in the CLBP groups was significantly more pronounced.Whether this change was an adaptive remodeling or alterations associated with chronic FJ osteoarthropathy should warrant further longitudinal studies.展开更多
The configuration of underground powerhouses is crucial in pumped-storage hydropower projects,which play a vital role in maintaining grid stability,facilitating the integration of renewable energy sources,and managing...The configuration of underground powerhouses is crucial in pumped-storage hydropower projects,which play a vital role in maintaining grid stability,facilitating the integration of renewable energy sources,and managing flood risks.However,geotechnical challenges,such as complex joint orientations,anisotropy in in-situ stress,and rock damage caused by excavation,require thorough stability assessments.This research employs the ubiquitous anisotropic joint model within FLAC3D to investigate the effects of joint dip angle,joint dip direction,and the alignment of in-situ stress on the stability of surrounding rock formations.The key parameters analyzed include joint cohesion,friction angle,and the magnitude of in-situ stress.The numerical results indicate that deformation is minimized when the axis of the powerhouse is aligned with the major principal stress.Furthermore,joint dip angles between 65°and 70°lead to a 50%reduction in both displacement and plastic zone volume.Additionally,angles less than 40°between the joint dip direction and the powerhouse axis enhance stability.These findings provide practical recommendations for optimizing the orientation of powerhouses in geomechanical contexts similar to those characterized by foliated sericite phyllite with moderate joint persistence.展开更多
Anisotropic strength and deformability of the rock mass with non-persistent joints are governed by cracking process of the rock bridges. The dependence of cracking process of jointed rock masses on the two important g...Anisotropic strength and deformability of the rock mass with non-persistent joints are governed by cracking process of the rock bridges. The dependence of cracking process of jointed rock masses on the two important geometrical parameters, joint orientation and joint persistence, was studied systematically by carrying out a series of uniaxial compression tests on gypsum specimens with regularly arranged multiple parallel pre-existing joints. According to crack position, mechanism and temporal sequence, seven types of crack initiations and sixteen types of crack coalescences, were identified. It was observed that both tensile cracks and shear cracks can emanate from the pre-existing joints as well as the matrix. Vertical joints were included and coplanar tensile cracks initiation and coalescence were observed accordingly. For specimen with joint inclination angle ,8=75~, it was found that collinear joints can be linked not only by coplanar shear cracks but also by mixed tensile-shear cracks, and that a pair of them can form a small rotation block. Seven failure modes, including axial cleavage, crushing, crushing and rotation of new blocks, stepped failure, stepped failure and rotation of new blocks, shear failure along a single plane and shear failure along multiple planes, were observed. These modes shift gradually in accordance with the combined variation of joint orientation and joint persistence. It is concluded that cracking process and failure modes are more strongly affected by joint orientation than by joint persistence, especially when joint inclination angle is larger than 45~. Finally, variations of macroscopic mechanical behaviors with the two geometrical parameters, such as patterns of the complete axial stress-axial strain curves, peak strength and elastic modulus, are summarized and their mechanisms are successfully explained according to their different cracking process.展开更多
文摘This paper describes the influence of joint spacing and joint orientation on the penetration rate of a Tunnel Boring Machine （TBM） disc cutter as modeled by the Discrete Element Method （DEM）. The input data for the siLmulations were obtained from the sandstone along the AIborz tunnel that is currently being excavated in Iran using a 5.2 m diameter open TBM. Three joint spacings, 150, 200, and 300 mm, were modeled together with seven values of joint orientation; 0°, 15°, 30°, 45°, 60°, 75°, and 90°. The results show that the penetration increases when joint orientation increases from 0° to 75°, but it decreases as the joint orientation increases further from 75° to 90°. This is true for each joint spacing. In addition, for a given joint orientation increasing the joint spacing causes the TBM penetration to decrease. The optimum joint orientation, from the viewpoint of TBM penetration, is about 60-75°.
文摘Objective:To examine the relationship between changes in lumbar spine facet joint(FJ)orientation and chronic low back pain(CLBP).Methods:We retrospectively analyzed lumbar spine CT and MRI images of 98 patients referred for localized paraspinal CLBP and 98 age-and sex-matched asymptomatic individuals as controls.They were divided into four age groups(A,<40;B,41-50;C,51-60;D,61-70;and E,71-80 years old,respectively).FJ orientations were evaluated at the L3-4,L4-5,and L5-S1 lumbar levels.Results:FJ angle showed a statistically significant more sagittal orientation in CLBP patients than in control groups in lower lumbar spine segments.The overall mean FJ angles in CLBP groups including all age groups combined at L3-4,L4-5,and L5-S1 levels were 32.33±4.5,36.11±2.9,and 37.4±6.1,degrees,respectively.The FJ angles in control group for all ages were 32.21±3.7,38.01±4.6,and 40.18±6.8°,respectively.The differences in FJ angle were statistically significant at both L4-5 and L5-S1 levels between the control and the CLBP groups(p<0.01).The FJ orientation from upper lumbar spine to lumbar sacral junction demonstrated a gradual more coronal orientation transition in all subjects but this trend was significantly less in CLBP patients.The mean FJ angles for the control group at age groups A,B,C,D,and E were 33.52±3.8,35.7±4.5,38.25±2.4,35.49±4.1,and 38.13±5.8,respectively,while those in the CLBP groups were 35.63±2.4,35.26±3.6,35.99±5.1,35.3±4.3,and 35.17±6.7,respectively.Conclusion:There is a significant association between a more sagittal FJ orientation and facetogenic CLBP in lower lumbar vertebral levels.There is also age-dependent decrease in FJ orientation in sagittal plane at lower lumbar spinal levels in control as well as CLBP groups,however,this decrease in the CLBP groups was significantly more pronounced.Whether this change was an adaptive remodeling or alterations associated with chronic FJ osteoarthropathy should warrant further longitudinal studies.
文摘The configuration of underground powerhouses is crucial in pumped-storage hydropower projects,which play a vital role in maintaining grid stability,facilitating the integration of renewable energy sources,and managing flood risks.However,geotechnical challenges,such as complex joint orientations,anisotropy in in-situ stress,and rock damage caused by excavation,require thorough stability assessments.This research employs the ubiquitous anisotropic joint model within FLAC3D to investigate the effects of joint dip angle,joint dip direction,and the alignment of in-situ stress on the stability of surrounding rock formations.The key parameters analyzed include joint cohesion,friction angle,and the magnitude of in-situ stress.The numerical results indicate that deformation is minimized when the axis of the powerhouse is aligned with the major principal stress.Furthermore,joint dip angles between 65°and 70°lead to a 50%reduction in both displacement and plastic zone volume.Additionally,angles less than 40°between the joint dip direction and the powerhouse axis enhance stability.These findings provide practical recommendations for optimizing the orientation of powerhouses in geomechanical contexts similar to those characterized by foliated sericite phyllite with moderate joint persistence.
基金Project(11102224)supported by the National Natural Science Foundation of ChinaProject(2009QL05)supported by the Fundamental Research Funds for the Central Universities of China
文摘Anisotropic strength and deformability of the rock mass with non-persistent joints are governed by cracking process of the rock bridges. The dependence of cracking process of jointed rock masses on the two important geometrical parameters, joint orientation and joint persistence, was studied systematically by carrying out a series of uniaxial compression tests on gypsum specimens with regularly arranged multiple parallel pre-existing joints. According to crack position, mechanism and temporal sequence, seven types of crack initiations and sixteen types of crack coalescences, were identified. It was observed that both tensile cracks and shear cracks can emanate from the pre-existing joints as well as the matrix. Vertical joints were included and coplanar tensile cracks initiation and coalescence were observed accordingly. For specimen with joint inclination angle ,8=75~, it was found that collinear joints can be linked not only by coplanar shear cracks but also by mixed tensile-shear cracks, and that a pair of them can form a small rotation block. Seven failure modes, including axial cleavage, crushing, crushing and rotation of new blocks, stepped failure, stepped failure and rotation of new blocks, shear failure along a single plane and shear failure along multiple planes, were observed. These modes shift gradually in accordance with the combined variation of joint orientation and joint persistence. It is concluded that cracking process and failure modes are more strongly affected by joint orientation than by joint persistence, especially when joint inclination angle is larger than 45~. Finally, variations of macroscopic mechanical behaviors with the two geometrical parameters, such as patterns of the complete axial stress-axial strain curves, peak strength and elastic modulus, are summarized and their mechanisms are successfully explained according to their different cracking process.
