Block size and shape depend on the state of fracturing of the rock mass and,consequently,on the geometrical features of the discontinuity sets(mainly orientation,spacing,and persistence).The development of non-contact...Block size and shape depend on the state of fracturing of the rock mass and,consequently,on the geometrical features of the discontinuity sets(mainly orientation,spacing,and persistence).The development of non-contact surveying techniques applied to rock mass characterization offers significant advantages in terms of data numerosity,precision,and accuracy,allowing for performing a rigorous statistical analysis of the database.This fact is particularly evident when dealing with rockfall phenomena:uncertainties in spacing and orientation data could significantly amplify the uncertainties connected with in situ block size distribution(IBSD),which represents a relation between each possible value of the volume and its probability of not being exceeded.In addition to volume,block shape can be considered as a derived parameter that suffers from uncertainties.Many attempts to model the possible trajectories of blocks considering their actual shape have been proposed,aiming to reproduce the effect on motion.The authors proposed analytical equations for calculating the expected value and variance of volume distributions,based on the geometrically correct equation for block volume in the case of three discontinuity sets.They quantify and discuss the effect of both volume and shape variability through a synthetic case study.Firstly,a fictitious rock mass with three discontinuity sets is assumed as the source of rockfall.The IBSDs obtained considering different spacing datasets are quantitatively compared,and the overall uncertainty effect is assessed,proving the correctness of the proposed equations.Then,block shape distributions are obtained and compared,confirming the variability of shapes within the same IBSD.Finally,a comparison between trajectory simulations on the synthetic slope is reported,aiming to highlight the effects of the propagation of uncertainties to block volume and shape estimation.The benefits of an approach that can quantify the uncertainties are discussed from the perspective of improving the reliabili展开更多
Analyzing large prehistoric rock avalanches provides significant data for evaluating the disaster posed by these relatively infrequent but destructive geological events. This paper attempts to study the characteristic...Analyzing large prehistoric rock avalanches provides significant data for evaluating the disaster posed by these relatively infrequent but destructive geological events. This paper attempts to study the characteristics and dynamics of the Ganqiuchi granitic rock avalanche, in the middle of the northern margin of Qinling Mountains, 30 km to the south of Xi’an, Shaanxi Province, China. In plane view, this rock avalanche is characterized by source area, accumulation area and dammed lake area. Based on previous studies, historical records and regional geological data, the major trigger of the Ganqiuchi rock avalanche is considered to be a strong paleo-earthquake with tremendous energy. The in situ deposit block size distributions of the intact rock mass and the debris deposits are presented and analyzed by using a simple model for estimating the number of fragmentation cycles that the blocks underwent. The results show that the primary controlling factor of the fragmentation process is the pre-existing fractures, and there is a relationship between the potential energy and the fragmentation energy: the latter is approximately 20% of the former. Based on the dynamic discrete element technique, the study proposes a four-stage model for the dynamic course of the Ganqiuchi rock avalanche:(1) failing;(2) highspeed sliding;(3) collision with obstacles;(4) decelerated sliding, which has implication for hazard assessment of the potential rock avalanches in China and other countries with similar geological setting.展开更多
文摘Block size and shape depend on the state of fracturing of the rock mass and,consequently,on the geometrical features of the discontinuity sets(mainly orientation,spacing,and persistence).The development of non-contact surveying techniques applied to rock mass characterization offers significant advantages in terms of data numerosity,precision,and accuracy,allowing for performing a rigorous statistical analysis of the database.This fact is particularly evident when dealing with rockfall phenomena:uncertainties in spacing and orientation data could significantly amplify the uncertainties connected with in situ block size distribution(IBSD),which represents a relation between each possible value of the volume and its probability of not being exceeded.In addition to volume,block shape can be considered as a derived parameter that suffers from uncertainties.Many attempts to model the possible trajectories of blocks considering their actual shape have been proposed,aiming to reproduce the effect on motion.The authors proposed analytical equations for calculating the expected value and variance of volume distributions,based on the geometrically correct equation for block volume in the case of three discontinuity sets.They quantify and discuss the effect of both volume and shape variability through a synthetic case study.Firstly,a fictitious rock mass with three discontinuity sets is assumed as the source of rockfall.The IBSDs obtained considering different spacing datasets are quantitatively compared,and the overall uncertainty effect is assessed,proving the correctness of the proposed equations.Then,block shape distributions are obtained and compared,confirming the variability of shapes within the same IBSD.Finally,a comparison between trajectory simulations on the synthetic slope is reported,aiming to highlight the effects of the propagation of uncertainties to block volume and shape estimation.The benefits of an approach that can quantify the uncertainties are discussed from the perspective of improving the reliabili
基金financially supported by the National Natural Science Foundation of China(grant numbers 4167020392)the State Key Laboratory Foundation of Geohazard Prevention and Geoenvironment Protection(SKLGP2018K015)the Geological Investigation Project fromChina Geological Survey(DD20160336)
文摘Analyzing large prehistoric rock avalanches provides significant data for evaluating the disaster posed by these relatively infrequent but destructive geological events. This paper attempts to study the characteristics and dynamics of the Ganqiuchi granitic rock avalanche, in the middle of the northern margin of Qinling Mountains, 30 km to the south of Xi’an, Shaanxi Province, China. In plane view, this rock avalanche is characterized by source area, accumulation area and dammed lake area. Based on previous studies, historical records and regional geological data, the major trigger of the Ganqiuchi rock avalanche is considered to be a strong paleo-earthquake with tremendous energy. The in situ deposit block size distributions of the intact rock mass and the debris deposits are presented and analyzed by using a simple model for estimating the number of fragmentation cycles that the blocks underwent. The results show that the primary controlling factor of the fragmentation process is the pre-existing fractures, and there is a relationship between the potential energy and the fragmentation energy: the latter is approximately 20% of the former. Based on the dynamic discrete element technique, the study proposes a four-stage model for the dynamic course of the Ganqiuchi rock avalanche:(1) failing;(2) highspeed sliding;(3) collision with obstacles;(4) decelerated sliding, which has implication for hazard assessment of the potential rock avalanches in China and other countries with similar geological setting.
