The long-term stability of rocks is crucial for ensuring safety in deep engineering,where the prolonged influence of shear loading is a key factor in delayed engineering disasters.Despite its significance,research on ...The long-term stability of rocks is crucial for ensuring safety in deep engineering,where the prolonged influence of shear loading is a key factor in delayed engineering disasters.Despite its significance,research on time-dependent shear failures under true triaxial stress to reflect in situ stress conditions remains limited.This study presents laboratory shear creep measurements on intact sandstone samples under constant normal load(CNL)and constant normal stiffness(CNS)conditions,which are typical of shallow and deep engineering cases,respectively.Our investigation focuses on the effects of various lateral stresses and boundary conditions on the mechanical behaviors and failure modes of the rock samples.Results indicate that lateral stress significantly reduces shear creep deformation and decreases creep rates.Without lateral stress constraints,the samples are prone to lateral tensile fractures leading to macroscopic spalling,likely due to“shear-induced tensile”stress.This failure behavior is mitigated under lateral stress constraints.Additionally,compared to CNL condition,samples under CNS condition demonstrate enhanced long-term shear resistance,reduced shear creep rates,and rougher shear failure surfaces.These findings suggest the need to improve our understanding of rock mass stability and to develop effective disaster prevention and mitigation strategies in engineering applications.展开更多
Rock bolts are widely used in rock engineering projects to improve the shear capacity of the jointed rock mass.The bolt inclination angle with respect to the shear plane has a remarkable influence on the bolting perfo...Rock bolts are widely used in rock engineering projects to improve the shear capacity of the jointed rock mass.The bolt inclination angle with respect to the shear plane has a remarkable influence on the bolting performance.In this study,a new artificial molding method based on 3D scanning and printing technology was first proposed to prepare bolted joints with an inclined bolt.Then,the effects of the bolt inclination angle and boundary conditions on the shear behavior and failure characteristic of bolted joints were addressed by conducting direct shear tests under both CNL and CNS conditions.Results indicated that rock bolt could significantly improve the shear behavior of rock joints,especially in the post-yield deformation region.With the increase of bolt inclination angle,both the maximum shear stress and the maximum friction coefficient increased first and then decreased,while the maximum normal displacement decreased monotonously.Compared with CNL conditions,the maximum shear stress was larger,whereas the maximum normal displacement and friction coefficient were smaller under the CNS conditions.Furthermore,more asperity damage was observed under the CNS conditions due to the increased normal stress on the shear plane.展开更多
对AHRI Standard 210/240-2017标准中关于HSPF的计算方法进行分析,并对一台额定制热量为17kW的北美定速房间空调器进行试验研究,分析室内风量、室外风量、制冷剂充注量以及制热衰减系数CD对制热季节能效HSPF的影响。结果表明:合理的室...对AHRI Standard 210/240-2017标准中关于HSPF的计算方法进行分析,并对一台额定制热量为17kW的北美定速房间空调器进行试验研究,分析室内风量、室外风量、制冷剂充注量以及制热衰减系数CD对制热季节能效HSPF的影响。结果表明:合理的室内机风量(额定风量100%)有助于提升系统的HSPF;过高的室外风量(超过额定风量100%)对系统的制热能力提升影响并不大,风机功率的增加反而导致HSPF明显下降;存在最佳充注量使HSPF最大,充注量偏大时,在除霜工况下,蒸发器结霜换热恶化,功耗增大,能效降低,且压缩机有湿压缩风险;HSPF随制热衰减系数CD值增大呈下降的趋势,因此,优化设计热泵系统的同时,降低CD值是一种提高HSPF比较直接、经济的途径。展开更多
基金support from the National Natural Science Foundation of China(Grant No.52209125).
文摘The long-term stability of rocks is crucial for ensuring safety in deep engineering,where the prolonged influence of shear loading is a key factor in delayed engineering disasters.Despite its significance,research on time-dependent shear failures under true triaxial stress to reflect in situ stress conditions remains limited.This study presents laboratory shear creep measurements on intact sandstone samples under constant normal load(CNL)and constant normal stiffness(CNS)conditions,which are typical of shallow and deep engineering cases,respectively.Our investigation focuses on the effects of various lateral stresses and boundary conditions on the mechanical behaviors and failure modes of the rock samples.Results indicate that lateral stress significantly reduces shear creep deformation and decreases creep rates.Without lateral stress constraints,the samples are prone to lateral tensile fractures leading to macroscopic spalling,likely due to“shear-induced tensile”stress.This failure behavior is mitigated under lateral stress constraints.Additionally,compared to CNL condition,samples under CNS condition demonstrate enhanced long-term shear resistance,reduced shear creep rates,and rougher shear failure surfaces.These findings suggest the need to improve our understanding of rock mass stability and to develop effective disaster prevention and mitigation strategies in engineering applications.
基金Project(U1865203)supported by the Key Projects of the Yalong River Joint Fund of the National Natural Science Foundation of ChinaProject(51279201)supported by the National Natural Science Foundation of ChinaProjects(2019YFC0605103,2019YFC0605100)supported by the National Key R&D Program of China。
文摘Rock bolts are widely used in rock engineering projects to improve the shear capacity of the jointed rock mass.The bolt inclination angle with respect to the shear plane has a remarkable influence on the bolting performance.In this study,a new artificial molding method based on 3D scanning and printing technology was first proposed to prepare bolted joints with an inclined bolt.Then,the effects of the bolt inclination angle and boundary conditions on the shear behavior and failure characteristic of bolted joints were addressed by conducting direct shear tests under both CNL and CNS conditions.Results indicated that rock bolt could significantly improve the shear behavior of rock joints,especially in the post-yield deformation region.With the increase of bolt inclination angle,both the maximum shear stress and the maximum friction coefficient increased first and then decreased,while the maximum normal displacement decreased monotonously.Compared with CNL conditions,the maximum shear stress was larger,whereas the maximum normal displacement and friction coefficient were smaller under the CNS conditions.Furthermore,more asperity damage was observed under the CNS conditions due to the increased normal stress on the shear plane.
文摘对AHRI Standard 210/240-2017标准中关于HSPF的计算方法进行分析,并对一台额定制热量为17kW的北美定速房间空调器进行试验研究,分析室内风量、室外风量、制冷剂充注量以及制热衰减系数CD对制热季节能效HSPF的影响。结果表明:合理的室内机风量(额定风量100%)有助于提升系统的HSPF;过高的室外风量(超过额定风量100%)对系统的制热能力提升影响并不大,风机功率的增加反而导致HSPF明显下降;存在最佳充注量使HSPF最大,充注量偏大时,在除霜工况下,蒸发器结霜换热恶化,功耗增大,能效降低,且压缩机有湿压缩风险;HSPF随制热衰减系数CD值增大呈下降的趋势,因此,优化设计热泵系统的同时,降低CD值是一种提高HSPF比较直接、经济的途径。
