As an important soil and water conservation engineering measure,more than 100,000 check dams are constructed across the Loess Plateau;these dams play a vital role in reducing floods and sediment in the region.However,...As an important soil and water conservation engineering measure,more than 100,000 check dams are constructed across the Loess Plateau;these dams play a vital role in reducing floods and sediment in the region.However,the effects of check dams on hydrologic process are still unclear,particularly when they are deployed as a system for watershed soil and water management.This study examined the watershed hydrologic process modulated by the check dam system in a typical Loess Plateau catchment.By simulating scenarios with various numbers of check dams using a distributed physically-based hydro-logical model,the effects of the number of check dams on runoff generation and concentration were analyzed for the study catchment.The results showed that the presence of check dams reduced the peak discharge and the flood volume and extended the flood duration;the reduction effect on peak discharge was most significant among the three factors.The system of check dams substantially decreased the runoff coefficient,and the runoff coefficient reduction rate was greater for rainstorms with shorter return periods than for rainstorms with longer return periods.The check dams increased the capacity of the catchment regulating and storing floods and extended the average runoff concentration time in the catchment that flattened the instantaneous unit hydrograph.This study reveals the influencing mech-anism of check dam system on the watershed hydrological process under heavy rainstorm conditions and provides a theoretical basis for evaluating the effects of numerous check dams on regional hydrology and water resources on the Loess Plateau.展开更多
A road cave-in accident caused by tunneling is described,and the possible mechanism of failure is analyzed.The cave-in measured about 30 m×27 m in plane,and about 15 m in depth.At about 19 m below the ground surf...A road cave-in accident caused by tunneling is described,and the possible mechanism of failure is analyzed.The cave-in measured about 30 m×27 m in plane,and about 15 m in depth.At about 19 m below the ground surface at the site,a tunnel construction was underway.Immediately above the tunnel,there was a weathered shale layer approximately t 2.66 m thick;above this layer,there were sand and gravel layers.The groundwater level was estimated to be about 5 m below the ground surface.By arch analysis,it is shown that the most likely cause of the accident was the low strength of the weathered shale layer and the high water pressure above the tunnel,which resulted in tensile failure of the weathered shale layer.The All Ground Fasten(AGF)pre-support measure was adopted,but it might make very limited contribution to the increase in the tensile strength of the shale layer in the cross-sectional direction of the tunnel.展开更多
基金This research was supported by the National Natural Science Foundation of China(51779204,51879281,5207910)Program for Science&Technology Innovation Research Team of Shaanxi Province(2018TD-037)the Research Fund of the State Key Laboratory of Eco-hydraulics in Northwest Arid Region,Xi'an University of Technology(Grant No.2018KFKT-1).
文摘As an important soil and water conservation engineering measure,more than 100,000 check dams are constructed across the Loess Plateau;these dams play a vital role in reducing floods and sediment in the region.However,the effects of check dams on hydrologic process are still unclear,particularly when they are deployed as a system for watershed soil and water management.This study examined the watershed hydrologic process modulated by the check dam system in a typical Loess Plateau catchment.By simulating scenarios with various numbers of check dams using a distributed physically-based hydro-logical model,the effects of the number of check dams on runoff generation and concentration were analyzed for the study catchment.The results showed that the presence of check dams reduced the peak discharge and the flood volume and extended the flood duration;the reduction effect on peak discharge was most significant among the three factors.The system of check dams substantially decreased the runoff coefficient,and the runoff coefficient reduction rate was greater for rainstorms with shorter return periods than for rainstorms with longer return periods.The check dams increased the capacity of the catchment regulating and storing floods and extended the average runoff concentration time in the catchment that flattened the instantaneous unit hydrograph.This study reveals the influencing mech-anism of check dam system on the watershed hydrological process under heavy rainstorm conditions and provides a theoretical basis for evaluating the effects of numerous check dams on regional hydrology and water resources on the Loess Plateau.
基金funded by National Key Basic Research Program of China(973 Program:2015CB057802).
文摘A road cave-in accident caused by tunneling is described,and the possible mechanism of failure is analyzed.The cave-in measured about 30 m×27 m in plane,and about 15 m in depth.At about 19 m below the ground surface at the site,a tunnel construction was underway.Immediately above the tunnel,there was a weathered shale layer approximately t 2.66 m thick;above this layer,there were sand and gravel layers.The groundwater level was estimated to be about 5 m below the ground surface.By arch analysis,it is shown that the most likely cause of the accident was the low strength of the weathered shale layer and the high water pressure above the tunnel,which resulted in tensile failure of the weathered shale layer.The All Ground Fasten(AGF)pre-support measure was adopted,but it might make very limited contribution to the increase in the tensile strength of the shale layer in the cross-sectional direction of the tunnel.
