Bedding structural planes significantly influence the mechanical properties and stability of engineering rock masses.This study conducts uniaxial compression tests on layered sandstone with various bedding angles(0...Bedding structural planes significantly influence the mechanical properties and stability of engineering rock masses.This study conducts uniaxial compression tests on layered sandstone with various bedding angles(0°,15°,30°,45°,60°,75°and 90°)to explore the impact of bedding angle on the deformational mechanical response,failure mode,and damage evolution processes of rocks.It develops a damage model based on the Logistic equation derived from the modulus’s degradation considering the combined effect of the sandstone bedding dip angle and load.This model is employed to study the damage accumulation state and its evolution within the layered rock mass.This research also introduces a piecewise constitutive model that considers the initial compaction characteristics to simulate the whole deformation process of layered sandstone under uniaxial compression.The results revealed that as the bedding angle increases from 0°to 90°,the uniaxial compressive strength and elastic modulus of layered sandstone significantly decrease,slightly increase,and then decline again.The corresponding failure modes transition from splitting tensile failure to slipping shear failure and back to splitting tensile failure.As indicated by the modulus’s degradation,the damage characteristics can be categorized into four stages:initial no damage,damage initiation,damage acceleration,and damage deceleration termination.The theoretical damage model based on the Logistic equation effectively simulates and predicts the entire damage evolution process.Moreover,the theoretical constitutive model curves closely align with the actual stress−strain curves of layered sandstone under uniaxial compression.The introduced constitutive model is concise,with fewer parameters,a straightforward parameter determination process,and a clear physical interpretation.This study offers valuable insights into the theory of layered rock mechanics and holds implications for ensuring the safety of rock engineering.展开更多
目的:探讨不同病因所致的大血管闭塞性脑卒中患者在亚急性期磁敏感血管征(susceptibility vessel sign,SVS)的表现。方法:选择北京大学第一医院神经内科病房2017年12月—2019年8月收治的经磁共振血管成像、CT血管造影或数字减影血管造...目的:探讨不同病因所致的大血管闭塞性脑卒中患者在亚急性期磁敏感血管征(susceptibility vessel sign,SVS)的表现。方法:选择北京大学第一医院神经内科病房2017年12月—2019年8月收治的经磁共振血管成像、CT血管造影或数字减影血管造影证实存在颅内大血管闭塞,且在发病第3~14天接受磁敏感加权成像(susceptibility-weighted imaging,SWI)检查的卒中患者进行回顾性分析,对比心源性栓塞(cardioembolism,CE)和大动脉粥样硬化性卒中(large artery atherosclerosis,LAA)患者的SVS征出现情况。结果:共有51例患者进入分析,其中女19例、男32例,平均年龄(63.04±11.23)岁。两组患者在性别、高血压、糖尿病、冠心病、高脂血症、吸烟、入院美国国立卫生研究院卒中量表(National Institute of Health stroke scale,NIHSS)评分间差异均无统计学意义。与LAA组相比,CE组患者年龄更大,合并房颤的比例更高,差异有统计学意义(P<0.05)。共有30例患者表现为SVS征阳性,心源性栓塞组患者SVS征阳性率为30%,显著低于大动脉粥样硬化性卒中患者(65.9%),两组间差异有统计学意义(P=0.039)。在敏感度测试中仅纳入SWI检查时间在卒中后第7~14天的患者,两组间SVS征阳性率的差异仍有统计学意义(0 vs.72.7%,P=0.006)。以有无房颤分组,合并房颤的卒中患者SVS征阳性率为25%,显著低于无房颤的卒中患者(65.1%),两组间差异有统计学意义(P=0.043)。结论:大动脉闭塞性脑卒中发病的亚急性期,心源性栓塞患者的SVS征阳性率低于LAA亚型的卒中患者;SVS征在卒中不同亚型鉴别中的作用尚需要进一步大样本的病例研究来验证。展开更多
Rockburst is one of the major disasters in deep underground rock mechanics and engineering.The precursors of rockbursts play important roles in rockburst prediction.Strainburst experiments were performed under double-...Rockburst is one of the major disasters in deep underground rock mechanics and engineering.The precursors of rockbursts play important roles in rockburst prediction.Strainburst experiments were performed under double-face unloading on sandstone with horizontal bedding planes using an independently designed rockburst testing facility.P-wave propagation time during the tests was automatically recorded by the acoustic emission apparatus.The P-wave velocities were calculated in both two directions to analyze their patterns.To find a characteristic precursor for rockburst,the dynamic evolution of rock anisotropy during the rockburst test is quantified by the anisotropic coefficient k,defined as the ratio of the two P-wave velocities in the directions vertical to and parallel to the bedding planes.The results show that rockburst occurs on the two free surfaces asynchronously.The rockburst failure occurs in the following order:crack generation,rock peeling,particle ejection,and rock fracture.In the process of rockburst under double-face unloading,the potential evolution characteristics of anisotropy can be generalized as anisotropy-isotropy-anisotropy.The suddenly unloading induces damage in the rock and presents anisotropic coefficient k steeply increasing departing from one,i.e.,isotropy.The rocks with horizontal bedding planes will reach the isotropic state before rockburst,which could be considered as a characteristic precursor of this kind of rockburst.展开更多
基金Projects(52074299, 41941018) supported by the National Natural Science Foundation of ChinaProject(2023JCCXSB02) supported by the Fundamental Research Funds for the Central Universities,China。
基金Projects(52074299,41941018)supported by the National Natural Science Foundation of ChinaProject(2023JCCXSB02)supported by the Fundamental Research Funds for the Central Universities,China。
文摘Bedding structural planes significantly influence the mechanical properties and stability of engineering rock masses.This study conducts uniaxial compression tests on layered sandstone with various bedding angles(0°,15°,30°,45°,60°,75°and 90°)to explore the impact of bedding angle on the deformational mechanical response,failure mode,and damage evolution processes of rocks.It develops a damage model based on the Logistic equation derived from the modulus’s degradation considering the combined effect of the sandstone bedding dip angle and load.This model is employed to study the damage accumulation state and its evolution within the layered rock mass.This research also introduces a piecewise constitutive model that considers the initial compaction characteristics to simulate the whole deformation process of layered sandstone under uniaxial compression.The results revealed that as the bedding angle increases from 0°to 90°,the uniaxial compressive strength and elastic modulus of layered sandstone significantly decrease,slightly increase,and then decline again.The corresponding failure modes transition from splitting tensile failure to slipping shear failure and back to splitting tensile failure.As indicated by the modulus’s degradation,the damage characteristics can be categorized into four stages:initial no damage,damage initiation,damage acceleration,and damage deceleration termination.The theoretical damage model based on the Logistic equation effectively simulates and predicts the entire damage evolution process.Moreover,the theoretical constitutive model curves closely align with the actual stress−strain curves of layered sandstone under uniaxial compression.The introduced constitutive model is concise,with fewer parameters,a straightforward parameter determination process,and a clear physical interpretation.This study offers valuable insights into the theory of layered rock mechanics and holds implications for ensuring the safety of rock engineering.
文摘目的:探讨不同病因所致的大血管闭塞性脑卒中患者在亚急性期磁敏感血管征(susceptibility vessel sign,SVS)的表现。方法:选择北京大学第一医院神经内科病房2017年12月—2019年8月收治的经磁共振血管成像、CT血管造影或数字减影血管造影证实存在颅内大血管闭塞,且在发病第3~14天接受磁敏感加权成像(susceptibility-weighted imaging,SWI)检查的卒中患者进行回顾性分析,对比心源性栓塞(cardioembolism,CE)和大动脉粥样硬化性卒中(large artery atherosclerosis,LAA)患者的SVS征出现情况。结果:共有51例患者进入分析,其中女19例、男32例,平均年龄(63.04±11.23)岁。两组患者在性别、高血压、糖尿病、冠心病、高脂血症、吸烟、入院美国国立卫生研究院卒中量表(National Institute of Health stroke scale,NIHSS)评分间差异均无统计学意义。与LAA组相比,CE组患者年龄更大,合并房颤的比例更高,差异有统计学意义(P<0.05)。共有30例患者表现为SVS征阳性,心源性栓塞组患者SVS征阳性率为30%,显著低于大动脉粥样硬化性卒中患者(65.9%),两组间差异有统计学意义(P=0.039)。在敏感度测试中仅纳入SWI检查时间在卒中后第7~14天的患者,两组间SVS征阳性率的差异仍有统计学意义(0 vs.72.7%,P=0.006)。以有无房颤分组,合并房颤的卒中患者SVS征阳性率为25%,显著低于无房颤的卒中患者(65.1%),两组间差异有统计学意义(P=0.043)。结论:大动脉闭塞性脑卒中发病的亚急性期,心源性栓塞患者的SVS征阳性率低于LAA亚型的卒中患者;SVS征在卒中不同亚型鉴别中的作用尚需要进一步大样本的病例研究来验证。
基金Projects(41941018,51704298)supported by the National Natural Science Foundation of ChinaProject(2021JCCXSB03)supported by the Fundamental Research Funds for the Central Universities,China。
文摘Rockburst is one of the major disasters in deep underground rock mechanics and engineering.The precursors of rockbursts play important roles in rockburst prediction.Strainburst experiments were performed under double-face unloading on sandstone with horizontal bedding planes using an independently designed rockburst testing facility.P-wave propagation time during the tests was automatically recorded by the acoustic emission apparatus.The P-wave velocities were calculated in both two directions to analyze their patterns.To find a characteristic precursor for rockburst,the dynamic evolution of rock anisotropy during the rockburst test is quantified by the anisotropic coefficient k,defined as the ratio of the two P-wave velocities in the directions vertical to and parallel to the bedding planes.The results show that rockburst occurs on the two free surfaces asynchronously.The rockburst failure occurs in the following order:crack generation,rock peeling,particle ejection,and rock fracture.In the process of rockburst under double-face unloading,the potential evolution characteristics of anisotropy can be generalized as anisotropy-isotropy-anisotropy.The suddenly unloading induces damage in the rock and presents anisotropic coefficient k steeply increasing departing from one,i.e.,isotropy.The rocks with horizontal bedding planes will reach the isotropic state before rockburst,which could be considered as a characteristic precursor of this kind of rockburst.
