A comprehensive understanding of the dynamic frictional characteristics in rock joints under high normal load and strong confinement is essential for ensuring the safety of deep engineering construction and mitigating...A comprehensive understanding of the dynamic frictional characteristics in rock joints under high normal load and strong confinement is essential for ensuring the safety of deep engineering construction and mitigating geological disasters.This study conducted shear experiments on rough rock joints under displacement-controlled dynamic normal loads,investigating the shear behaviors of joints across varying initial normal loads,normal loading frequencies,and normal loading amplitudes.Experimental results showed that the peak/valley shear force values increased with initial normal loads and normal loading frequencies but showed an initial increase followed by a decrease with normal loading amplitudes.Dynamic normal loading can either increase or decrease shear strength,while this study demonstrates that higher frequencies lead to enhanced friction.Increased initial normal loading and normal loading frequency result in a gradual decrease in joint roughness coefficient(JRC)values of joint surfaces after shearing.Positive correlations existed between frictional energy dissipation and peak shear forces,while post-shear joint surface roughness exhibited a negative correlation with peak shear forces through linear regression analysis.This study contributes to a better understanding of the sliding responses and shear mechanical characteristics of rock joints under dynamic disturbances.展开更多
The alpine treeline ecotone is defined as a forest-grassland or forest-tundra transition boundary either between subalpine forest and treeless grassland,or between subalpine forest and treeless tundra.The alpine treel...The alpine treeline ecotone is defined as a forest-grassland or forest-tundra transition boundary either between subalpine forest and treeless grassland,or between subalpine forest and treeless tundra.The alpine treeline ecotone serves irreplaceable ecological functions and provides various ecosystem services.There are three lines associated with the alpine treeline ecotone,the tree species line(i.e.,the highest elevational limit of individual tree establishment and growth),the treeline(i.e.,the transition line between tree islands and isolated individual trees)and the timber line(i.e.,the upper boundary of the closed subalpine forest).The alpine treeline ecotone is the belt region between the tree species line and the timber line of the closed forest.The treeline is very sensitive to climate change and is often used as an indicator for the response of vegetation to global warming.However,there is currently no comprehensive review in the field of alpine treeline advance under global warming.Therefore,this review summarizes the literature and discusses the theoretical bases and challenges in the study of alpine treeline dynamics from the following four aspects:(1)Ecological functions and issues of treeline dynamics;(2)Methodology for monitoring treeline dynamics;(3)Treeline shifts in different climate zones;(4)Driving factors for treeline upward shifting.展开更多
基金Projects(52174092,51904290)supported by the National Natural Science Foundation,ChinaProject(BK20220157)supported by the Natural Science Foundation of Jiangsu Province,China+1 种基金Project(232102321009)supported by Henan Province Science and Technology Key Project,ChinaProject(2022YCPY0202)supported by Fundamental Research Funds for the Central Universities,China。
文摘A comprehensive understanding of the dynamic frictional characteristics in rock joints under high normal load and strong confinement is essential for ensuring the safety of deep engineering construction and mitigating geological disasters.This study conducted shear experiments on rough rock joints under displacement-controlled dynamic normal loads,investigating the shear behaviors of joints across varying initial normal loads,normal loading frequencies,and normal loading amplitudes.Experimental results showed that the peak/valley shear force values increased with initial normal loads and normal loading frequencies but showed an initial increase followed by a decrease with normal loading amplitudes.Dynamic normal loading can either increase or decrease shear strength,while this study demonstrates that higher frequencies lead to enhanced friction.Increased initial normal loading and normal loading frequency result in a gradual decrease in joint roughness coefficient(JRC)values of joint surfaces after shearing.Positive correlations existed between frictional energy dissipation and peak shear forces,while post-shear joint surface roughness exhibited a negative correlation with peak shear forces through linear regression analysis.This study contributes to a better understanding of the sliding responses and shear mechanical characteristics of rock joints under dynamic disturbances.
基金The National Natural Science Foundation of China(41901361)The Six Talent Peaks Project of Jiangsu Province(TD-XYDXX-006)+1 种基金The Natural Science Foundation of Jiangsu Province(BK20180769)The Major Basic Research Project of the Natural Science Foundation of theJiangsu Higher Education Institutions(18KJB180009).
文摘The alpine treeline ecotone is defined as a forest-grassland or forest-tundra transition boundary either between subalpine forest and treeless grassland,or between subalpine forest and treeless tundra.The alpine treeline ecotone serves irreplaceable ecological functions and provides various ecosystem services.There are three lines associated with the alpine treeline ecotone,the tree species line(i.e.,the highest elevational limit of individual tree establishment and growth),the treeline(i.e.,the transition line between tree islands and isolated individual trees)and the timber line(i.e.,the upper boundary of the closed subalpine forest).The alpine treeline ecotone is the belt region between the tree species line and the timber line of the closed forest.The treeline is very sensitive to climate change and is often used as an indicator for the response of vegetation to global warming.However,there is currently no comprehensive review in the field of alpine treeline advance under global warming.Therefore,this review summarizes the literature and discusses the theoretical bases and challenges in the study of alpine treeline dynamics from the following four aspects:(1)Ecological functions and issues of treeline dynamics;(2)Methodology for monitoring treeline dynamics;(3)Treeline shifts in different climate zones;(4)Driving factors for treeline upward shifting.
