Some novel techniques of computational fluid dynamics are used to establish a mathematical model for the open diversion channel with two embankments in river blocking.The technique of boundary fitted coordinate syste...Some novel techniques of computational fluid dynamics are used to establish a mathematical model for the open diversion channel with two embankments in river blocking.The technique of boundary fitted coordinate system is used to overcome the difficulties resulting from the complicated shapes of natural river boundaries;the method of alternating direction implicit finite difference scheme is used to solve the partial differential equations in the transformed plane;and the technique of moving boundary is used to deal with the river bed exposed to water surface.This model has been used to predict the flow characteristics in the blocking of the Yangtz river in the Three Gorge Project (TGP).Comparison between the computed and experimental data shows a satisfactory agreement.展开更多
Many moraines formed between Daduka and Chibai in the Tsangpo River valley since Middle Pleistocene. A prominent set of lacustrine and alluvial terraces on the valley margin along both the Tsangpo and Nyang Rivers for...Many moraines formed between Daduka and Chibai in the Tsangpo River valley since Middle Pleistocene. A prominent set of lacustrine and alluvial terraces on the valley margin along both the Tsangpo and Nyang Rivers formed during Quaternary glacial epoch demonstrate lakes were created by damming of the river. Research was conducted on the geological environment, contained sediments, spatial distribution, timing, and formation and destruction of these paleolakes. The lacustrine sediments 14C （10537±268 aBP at Linzhi Brick and Tile Factory, 22510±580 aBP and 13925±204 aBP at Bengga, 21096±1466 aBP at Yusong） and a series of ESR （electron spin resonance） ages at Linzhi town and previous data by other experts, paleolakes persisted for 691±305 kaBP middle Pleistocene ice age, 75-40 kaBP the early stage of last glacier, 27-8 kaBP Last Glacier Maximum （LGM）, existence time of lakes gradually shorten represents glacial scale and dam moraine supply potential gradually cut down, paleolakes and dam scale also gradually diminished. This article calculated the average lacustrine sedimentary rate of Gega paleolake in LGM was 12.5 mm/a, demonstrates Mount Namjagbarwa uplifted strongly at the same time, the sedimentary rate of Gega paleolake is more larger than that of enclosed lakes of plateau inland shows the climatic variation of Mount Namjagbarwa is more larger and plateau margin uplifted more quicker than plateau inland. This article analyzed formation and decay cause about the Zelunglung glacier on the west flank of Mount Namjagbarwa got into the Tsangpo River valley and blocked it for tectonic and climatic factors. There is a site of blocking the valley from Gega to Chibai. This article according to moraines and lacustrine sediments yielded paleolakes scale： the lowest lake base altitude 2850 m, the highest lake surface altitude 3585 m, 3240 m and 3180 m, area 2885 km2, 820 km2 and 810 km2, lake maximum depth of 735 m, 390 m and 330 m. We disclose the reason that previous experts discovered there were different age moraines dividing line of altitude 3180 m at the entrance of the Tsangpo Grand Canyon is dammed lake erosive decay under altitude 3180 m moraines in the last glacier era covering moraines in the early ice age of late Pleistocene, top 3180 m in the last glacier moraine remained because ancient dammed lakes didn＇t erode it under 3180 m moraines in the early ice age of late Pleistocene exposed. The reason of the top elevation 3585 m moraines in the middle Pleistocene ice age likes that of altitude 3180 m. There were three times dammed lakes by glacier blocking the Tsangpo River during Quaternary glacial period. During other glacial and interglacial period the Zelunglung glacier often extended the valley but moraine supplemental speed of the dam was smaller than that of fluvial erosion and moraine movement, dam quickly disappeared and didn＇t form stable lake.展开更多
A large number of giant paleo-landslides were found in the section from Lagan Gorge to Liujia Gorge,which is located in the upper reaches of the Yellow River.This area is located in the transition zone between the Qin...A large number of giant paleo-landslides were found in the section from Lagan Gorge to Liujia Gorge,which is located in the upper reaches of the Yellow River.This area is located in the transition zone between the Qinghai-Tibet Plateau and the Loess Plateau with a semi-arid climate.The occurrence of lacustrine deposits suggests that some of the giant landslides ever blocked the river and landslide-dammed lakes have occurred in this area.The chronology of the giant landslide in the upper Yellow River was obtained and analyzed by optically stimulated luminescence(OSL)dating and established a chronological framework combining previous data.From the perspective of space,there are five major landslide clusters in the upper Yellow River.They are mainly located in the canyons at the junction of the Yellow River valley,and the center of every basins,which are inextricably linked to the unique sedimentary and tectonic environments of each basin.From the perspective of time,giant landslides also tend to occur during interglacial or glacialto-interglacial transitions.Paleoseismicity and precipitation appear to be coupled and have competing relationships in their contribution to the formation of giant landslides.展开更多
Tangjiashan landslide is a typical high-speed consequent landslide of medium-steep dip angle. This landslide triggered by earthquake took place in about semi-minute. The relative sliding displacement is 900 meters, so...Tangjiashan landslide is a typical high-speed consequent landslide of medium-steep dip angle. This landslide triggered by earthquake took place in about semi-minute. The relative sliding displacement is 900 meters, so average sliding speed is about 30 meters per second. The longitudinal length of barrier dam which is formed by high-speed landslide along river is 803.4 meters; and maximum width crossing river is 611.8 meters. And its volume is estimated about 20.37 million steres. Through detailed geological investigation of the barrier dam, together with early geological information before earthquake, geological structures of the barrier dam and its stability of upstream and downstream slopes are studied when water level reaches different elevations in condition of continual after shocks with seismic intensity of 7 or 8 Richter scale. On this basis, dam-breaking mode of barrier dam is discussed deeply. Thereby, analytic results provide significant guidance and advices to front headquarters of Tangjiashan barrier dam, so that some proper engineering measures can be implemented and flood discharge can be carried out well.展开更多
This paper proposes the critical conditions for a submerged ice block beneath an intact ice cover to become unstable,as a fundamental component of any numerical model to successfully predict the ice jam formation or t...This paper proposes the critical conditions for a submerged ice block beneath an intact ice cover to become unstable,as a fundamental component of any numerical model to successfully predict the ice jam formation or the ice jam release events.The flume model experimental and numerical simulation methods are both applied to analyze the stability of submerged ice blocks.The flume model experiment is first conducted,and the experimental results indicate that the influencing factors of the stability of a submerged ice block include the relative length,the relative water depth and the relative width.It was shown that the effect of the relative width on the stability of submerged ice blocks was not well studied.Based on the experimental results,the k-eturbulence model is applied to establish a 3-D numerical model for studying the pressure distribution beneath submerged ice blocks.The effects of the relative width on the Venturi pressure and the leading edge pressure are evaluated.Finally,according to the force balance equation and the moment balance equation,this paper proposes a computational formula for the sliding and underturning critical conditions of submerged ice blocks,and the results are in good agreement with the experimental results.展开更多
文摘Some novel techniques of computational fluid dynamics are used to establish a mathematical model for the open diversion channel with two embankments in river blocking.The technique of boundary fitted coordinate system is used to overcome the difficulties resulting from the complicated shapes of natural river boundaries;the method of alternating direction implicit finite difference scheme is used to solve the partial differential equations in the transformed plane;and the technique of moving boundary is used to deal with the river bed exposed to water surface.This model has been used to predict the flow characteristics in the blocking of the Yangtz river in the Three Gorge Project (TGP).Comparison between the computed and experimental data shows a satisfactory agreement.
基金supported by Project No.1212011120185 sponsored by China Geological Survey
文摘Many moraines formed between Daduka and Chibai in the Tsangpo River valley since Middle Pleistocene. A prominent set of lacustrine and alluvial terraces on the valley margin along both the Tsangpo and Nyang Rivers formed during Quaternary glacial epoch demonstrate lakes were created by damming of the river. Research was conducted on the geological environment, contained sediments, spatial distribution, timing, and formation and destruction of these paleolakes. The lacustrine sediments 14C （10537±268 aBP at Linzhi Brick and Tile Factory, 22510±580 aBP and 13925±204 aBP at Bengga, 21096±1466 aBP at Yusong） and a series of ESR （electron spin resonance） ages at Linzhi town and previous data by other experts, paleolakes persisted for 691±305 kaBP middle Pleistocene ice age, 75-40 kaBP the early stage of last glacier, 27-8 kaBP Last Glacier Maximum （LGM）, existence time of lakes gradually shorten represents glacial scale and dam moraine supply potential gradually cut down, paleolakes and dam scale also gradually diminished. This article calculated the average lacustrine sedimentary rate of Gega paleolake in LGM was 12.5 mm/a, demonstrates Mount Namjagbarwa uplifted strongly at the same time, the sedimentary rate of Gega paleolake is more larger than that of enclosed lakes of plateau inland shows the climatic variation of Mount Namjagbarwa is more larger and plateau margin uplifted more quicker than plateau inland. This article analyzed formation and decay cause about the Zelunglung glacier on the west flank of Mount Namjagbarwa got into the Tsangpo River valley and blocked it for tectonic and climatic factors. There is a site of blocking the valley from Gega to Chibai. This article according to moraines and lacustrine sediments yielded paleolakes scale： the lowest lake base altitude 2850 m, the highest lake surface altitude 3585 m, 3240 m and 3180 m, area 2885 km2, 820 km2 and 810 km2, lake maximum depth of 735 m, 390 m and 330 m. We disclose the reason that previous experts discovered there were different age moraines dividing line of altitude 3180 m at the entrance of the Tsangpo Grand Canyon is dammed lake erosive decay under altitude 3180 m moraines in the last glacier era covering moraines in the early ice age of late Pleistocene, top 3180 m in the last glacier moraine remained because ancient dammed lakes didn＇t erode it under 3180 m moraines in the early ice age of late Pleistocene exposed. The reason of the top elevation 3585 m moraines in the middle Pleistocene ice age likes that of altitude 3180 m. There were three times dammed lakes by glacier blocking the Tsangpo River during Quaternary glacial period. During other glacial and interglacial period the Zelunglung glacier often extended the valley but moraine supplemental speed of the dam was smaller than that of fluvial erosion and moraine movement, dam quickly disappeared and didn＇t form stable lake.
基金supported by the National Natural Science Foundation of China(Grant No.42041006)the China Scholarship Council Studentship Awarded to Yi-Qi Ji(Ref.202206560049)。
文摘A large number of giant paleo-landslides were found in the section from Lagan Gorge to Liujia Gorge,which is located in the upper reaches of the Yellow River.This area is located in the transition zone between the Qinghai-Tibet Plateau and the Loess Plateau with a semi-arid climate.The occurrence of lacustrine deposits suggests that some of the giant landslides ever blocked the river and landslide-dammed lakes have occurred in this area.The chronology of the giant landslide in the upper Yellow River was obtained and analyzed by optically stimulated luminescence(OSL)dating and established a chronological framework combining previous data.From the perspective of space,there are five major landslide clusters in the upper Yellow River.They are mainly located in the canyons at the junction of the Yellow River valley,and the center of every basins,which are inextricably linked to the unique sedimentary and tectonic environments of each basin.From the perspective of time,giant landslides also tend to occur during interglacial or glacialto-interglacial transitions.Paleoseismicity and precipitation appear to be coupled and have competing relationships in their contribution to the formation of giant landslides.
基金funding from the National Natural Science Foundation Project (Grant No. 40772175, 40972175)the Scientific research fund of Southwest Jiaotong University (Grant No.2008-A01)+1 种基金the Opening Fund of State Key Laboratory of Geohazard Prevention and Geoenvironment Protection (Chengdu University of Technology) (Grant No. DZKJ–08012)the National Natural Science Foundation Project-mutual fund of Yunnan Province (Grant No.U1033601)
文摘Tangjiashan landslide is a typical high-speed consequent landslide of medium-steep dip angle. This landslide triggered by earthquake took place in about semi-minute. The relative sliding displacement is 900 meters, so average sliding speed is about 30 meters per second. The longitudinal length of barrier dam which is formed by high-speed landslide along river is 803.4 meters; and maximum width crossing river is 611.8 meters. And its volume is estimated about 20.37 million steres. Through detailed geological investigation of the barrier dam, together with early geological information before earthquake, geological structures of the barrier dam and its stability of upstream and downstream slopes are studied when water level reaches different elevations in condition of continual after shocks with seismic intensity of 7 or 8 Richter scale. On this basis, dam-breaking mode of barrier dam is discussed deeply. Thereby, analytic results provide significant guidance and advices to front headquarters of Tangjiashan barrier dam, so that some proper engineering measures can be implemented and flood discharge can be carried out well.
基金supported by the Funds for Creative Research Groups of China(Grant No.51321065)the Tianjin Municipal Science and Technology Project(Grant No.13JCZDJC35100)
文摘This paper proposes the critical conditions for a submerged ice block beneath an intact ice cover to become unstable,as a fundamental component of any numerical model to successfully predict the ice jam formation or the ice jam release events.The flume model experimental and numerical simulation methods are both applied to analyze the stability of submerged ice blocks.The flume model experiment is first conducted,and the experimental results indicate that the influencing factors of the stability of a submerged ice block include the relative length,the relative water depth and the relative width.It was shown that the effect of the relative width on the stability of submerged ice blocks was not well studied.Based on the experimental results,the k-eturbulence model is applied to establish a 3-D numerical model for studying the pressure distribution beneath submerged ice blocks.The effects of the relative width on the Venturi pressure and the leading edge pressure are evaluated.Finally,according to the force balance equation and the moment balance equation,this paper proposes a computational formula for the sliding and underturning critical conditions of submerged ice blocks,and the results are in good agreement with the experimental results.
