A new blasting approach of combined blastholes with different diameters is proposed to solve the problems of oversize boulders and rock toes in open-pit mine. A non-ideal detonation model and a statistical damage cons...A new blasting approach of combined blastholes with different diameters is proposed to solve the problems of oversize boulders and rock toes in open-pit mine. A non-ideal detonation model and a statistical damage constitutive model are implemented in dynamic finite element analysis to investigate the formation mechanism of oversize boulders and toes. The damage distribution and evolution process of rock blasting fragmentation is simulated, and the scheme is further optimized. Numerical analysis results showed that pocket charges and satellite blastholes can only improve bench top fragmentation, but they cannot reduce the oversize in the middle and bottom of bench as well as the toe problem. The new blasting approach of combined blastholes with different diameters can effectively reduce the oversize boulders and toes as well as the production costs.展开更多
Concrete dams are reliable when subjected to static loads such as earth pressure and water pressure.However,the dam failure would be abrupt and catastrophic if it is impacted by boulders.This study simulated the dynam...Concrete dams are reliable when subjected to static loads such as earth pressure and water pressure.However,the dam failure would be abrupt and catastrophic if it is impacted by boulders.This study simulated the dynamic response of flat dam,concave dam,and convex dam under the impact of boulders by using ANSYS/LS-DYNA finite element software.In the numerical simulation,the strain rate effect under the impact load is considered,and Holmquist-Johnson-Cook(HJC)model-a dynamic damage constitutive model is applied to concrete materials.Results show that the peak impact force of concave dam is minimum.Meanwhile,for different dam types(flat dam,concave dam,and convex dam)and impactor velocities(5,10,and 15 m/s),the impact force fluctuates with the height of the impact point and it reaches the maximum value when the height of the impact point is 2/3 of the dam height.Numerical simulation mainly considers different masses and velocities and obtains empirical formulae of impact force for three dam types.The established empirical formula for the flat dam is compared with the existing classical formula and several similar experimental tests.It was found that the newly empirical formulae are reasonable and effective,and it provides design suggestions for similar concrete dams.展开更多
Boulder spacing in mountain rivers and near-wake flow zones within the boulder array is very useful for fish habitat and growth of aquatic organisms.The present study aims to investigate how the boulder array and spac...Boulder spacing in mountain rivers and near-wake flow zones within the boulder array is very useful for fish habitat and growth of aquatic organisms.The present study aims to investigate how the boulder array and spacing influence the near-bed flow structures in a gravel-bed stream.Boulders are staggered over a gravel-bed stream with three different inter-boulder spacing namely(a)large(b)medium and(c)small spacing.An acoustic Doppler velocimeter was used for flow measurements in a rectangular channel and the results were compared with those acquired from numerical simulation.The time-averaged velocity profiles at the near-wake flow zones of boulders experience maximum flow retardation which is an outcome of the boulder-induced form roughness.The ratio of velocity differences associated to form and skin roughness and its positive magnitude reveals the dominance of form roughness closest to the boulders.Form roughness computed is 1.75 to 2 times higher than the skin roughness at the near-wake flow region.In particular,the collective immobile boulders placed at different inter-boulder spacings developed high and low bed shear stresses closest to the boulders.The low bed shear stresses characterised by a secondary peak developed at the trough location of the boulders is attributed to the skin shear stress.Further,the spatial averaging of time-averaged flow quantities gives additional impetus to present an improved illustration of fluid shear stresses.The formation of form-induced shear stress is estimated to be 17%to 23%of doubleaveraged Reynolds shear stress and partially compensates for the damping of time-averaged Reynolds shear stress in the interfacial sub-layer.The quadrant analysis of spatial velocity fluctuations depicts that the form-induced shear stresses are dominant in the interfacial sub-layer and have no significance above the gravel-bed surface.展开更多
Extreme storm events in coastal zones play significant roles in shaping the morphology of boulder beaches.However,boulder displacement and the geomorphological evolution of boulder beaches driven by different extreme ...Extreme storm events in coastal zones play significant roles in shaping the morphology of boulder beaches.However,boulder displacement and the geomorphological evolution of boulder beaches driven by different extreme storm events,especially typhoon events,remain poorly understood.Thus,boulder displacement and the geomorphic response on a boulder beach in Fujian,southeastern China,were explored before,during and after a cold wave event(Dec.1–7,2020)and before and after Typhoon In-Fa(Jul.19–27,2021),a large tropical storm.This was achieved by tracking 42 tagged boulders distributed in the intertidal and supratidal zones using Radio Frequency Identification(RFID)and topographic surveys using real-time kinematic techniques,respectively.The results showed obvious disparities in boulder displacement in different geomorphic zones due to cold wave and typhoon events that were mainly characterized by migration magnitude,range,direction,and mode of transport.The typhoon event led to rapid and substantial changes in the overall morphology of the boulder beach,while the cold wave event impacted the intertidal morphology of the boulder beach to only a small extent.The surrounding structure of boulders,beach slope and beach elevation had a combined dominant effect on boulder displacement under the same extreme event.Hydrodynamic factors(effective wave energy fluxes,incident wave direction,storm surge and water level)had dominant effects on boulder displacement during different extreme events.In terms of a single event,the magnitude of the boulder displacement driven by the typhoon was much greater than that driven by the cold wave.However,considering the frequency and duration of cold waves in winter,the impact of multiple consecutive cold waves on the geomorphology of the boulder beach cannot be ignored in this study area.Alternating and repeated interactions between these two processes constitute the complete geomorphic evolution of the boulder beach.This study contributes to improved predictions of the morphodynamic response of boulder beaches to future storms,especially large tropical storms,and facilitates better coastal management.展开更多
This paper presents results from preliminary assessments in Ngasamo ward, Busega district in Simiyu region. The main objective was to assess cultural heritage assets in some areas of Bariadi district in Simiyu region....This paper presents results from preliminary assessments in Ngasamo ward, Busega district in Simiyu region. The main objective was to assess cultural heritage assets in some areas of Bariadi district in Simiyu region. Specific objectives of the assessment are to identify tangible cultural heritage resources in Simiyu region;to identify intangible cultural heritage resources in Simiyu region;and to provide suggestions for pertinent protection, conservation and presentation of cultural heritage resources. The assessment was carried out through surveys that included documentation together with records for Global Positioning System (GPS) coordinates per surveyed locality;key informant interviews;and Focus Group Discussion. Results from the assessment revealed several worship areas that include immovable physical objects associated to ritual performance places. For example, wells like Luhuhi in Ilula village, Nkindwa biye tree in Ilula village, Magahi well in Isenge village, Isangijo hill at Isenge village, Dutwa well in Isenge village, Nyabusalu well in Igalukilo village and similar others are worship places that were revealed by informants. The assessment uncovered granite rock boulders that are being chopped off flakes for traditional medicine use in the area. Some cultural heritage sites have been identified such that a lot more needs to be explored in order to establish existence of other physical cultural heritage sites in Busega district, Bariadi district. For example, the grinding hollows, bao and the like are unique heritage resources. Such resources including undiscovered immovable archaeological objects would need presentation of sustainable preservation as well as conservation plans in line with Antiquities Acts, Antiquities Rules and Monuments of 1980 together with Cultural Heritage Policy of 2008.展开更多
The impact effect of boulder within debris flow is the key factor contributing to peak impact as well as to the failure of debris flow control work. So accurate measuring and calculating the impact force of debris flo...The impact effect of boulder within debris flow is the key factor contributing to peak impact as well as to the failure of debris flow control work. So accurate measuring and calculating the impact force of debris flow can ensure the engineering design strength. However, limited to the existing laboratory conditions and piezoelectric sensor performance, it is impossible, based on the conventional measurements, to devise a computing method for expressing a reliable boulder impact force. This paper has therefore designed a new measurement device according to the method of integrating Fiber Bragg grating(FBG) and reinforced concrete composite beam(RCB) for measuring the impact force of debris flows, i.e. mounting FBG on the axially stressed steel bar in the composite beam at regular intervals to monitor the steel strain. RCB plays the role of contacting debris flow and protecting FBG sensors. Taking this new device as the experimental object, drop testing is designed for simulating and reflecting the boulder impact force. In a series of impacting tests, the relationship between the peak dynamic strain value of the steel bar and the impact force is analyzed, and based on which, an inversion model that uses the steel bar strain as the independent variable is established for calculating the boulder impact force.The experimental results show that this new inversion model can determine the impact force value and its acting position with a system error of 18.1%, which can provide an experimental foundation for measuring the impact force of boulders within the debris flow by the new FBG-based device.展开更多
Loose deposits, rainfall and topography are three key factors that triggering debris flows.However, few studies have investigated the effects of loose deposits on the whole debris flow process.On June 28, 2012, a cata...Loose deposits, rainfall and topography are three key factors that triggering debris flows.However, few studies have investigated the effects of loose deposits on the whole debris flow process.On June 28, 2012, a catastrophic debris flow occurred in the Aizi Valley, resulting in 40 deaths.The Aizi Valley is located in the Lower Jinsha River,southwestern Sichuan Province, China. The Aizi Valley debris flow has been selected as a case for addressing loose deposits effects on the whole debris flow process through remote sensing, field investigation and field experiments. Remote sensing interpretation and laboratory experiments were used to obtain the distribution and characteristics of the loose deposits, respectively. A field experiment was conducted to explore the mechanics of slope debris flows, and another field investigation was conducted to obtain the processes of debris flow formation, movement and amplification. The results showed that loose deposits preparation, slope debris flow initiation,gully debris flow confluence and valley debris flow amplification were dominated by the loose deposits.Antecedent droughts and earthquake activities may have increased the potential for loose soil sources in the Aizi Valley, which laid the foundation for debris flow formation. Slope debris flow initiated under rainfall, and the increase in the water content as well as the pore water pressure of the loose deposits were the key factors affecting slope failure. The nine gully debris flows converged in the valley, and the peak discharge was amplified 3.3 times due to a blockage and outburst caused by a large boulder. The results may help in predicting and assessing regional debris flows in dry-hot and seismic-prone areas based on loose deposits, especially considering large boulders.展开更多
The cover photo shows a big granite boulder named 'Anvil Stone', which is about 10 m high and is perching on another boulder. As its name suggests, the 'Anvil Stone' looks like an anvil due to its inwa...The cover photo shows a big granite boulder named 'Anvil Stone', which is about 10 m high and is perching on another boulder. As its name suggests, the 'Anvil Stone' looks like an anvil due to its inward concave sidewalls. The 'Anvil Stone' is located on a mountainous ridge of the Little Sangpu Mountain of eastern Guangdong, China at approximately 93 m above sea level. The mountain opposite the 'Anvil Stone' in the photo is the Great Sangpu Mountain. The plain between the Great and Little mountains represent a faulty depression formed by Dongshanhu fault.展开更多
The interlayer structure of braid river reservoirs is complex and the interwell prediction is difficult in offshore oil field. Taking CFD11-1 oilfield of NgⅢ sand as an example, based on layer contrasting, the interl...The interlayer structure of braid river reservoirs is complex and the interwell prediction is difficult in offshore oil field. Taking CFD11-1 oilfield of NgⅢ sand as an example, based on layer contrasting, the interlayer is divided into muddy interlayer, clay boulder interlayer, and physical interlayer according to lithology. Under the guidance of sedimentary model, we use the geology statistical inversion method to predict the clay boulder interlayer, consistent with the dynamic characteristics of oil production which is used for the prior quality control. The results of this study can objectively reveal the characteristics of interlayer space distribution. Compared with the traditional multi-well comparison and stochastic simulation model, this method is applied to the offshore oil field which is character with wide well space, sparse well network, which has very high application value in predicting the interlayer and deploying of inter-well encryption in the similar oilfield.展开更多
Boulders and cobbles are often used in stream restoration projects to increase flow resistance and enhance channel stability and habitat diversity. Particle size metrics determined from the particle distribution are o...Boulders and cobbles are often used in stream restoration projects to increase flow resistance and enhance channel stability and habitat diversity. Particle size metrics determined from the particle distribution are often used as a proxy for shear stress in field equations. Clustering of large particles has been thought to contribute to shear stress, but the effect of clustering is not accounted for in equations that use a representative particle size, such as the <em>D</em><sub>84</sub>. In this paper, clustering is defined using the upper tail (≥84%) in a variable called Topsum. The number of clusters, average size of clusters, and shear stress are evaluated using the proposed definition of cluster. Findings suggest that the upper tail represents the roughness height better than the commonly used proxy of <em>D</em><sub>84</sub> for boulder bed streams (streams which have a D84 particle 0.05 - 0.15 meters).展开更多
It is generally considered that four-times ice age happened during the Quaternary epoch on the Tibetan Plateau. However, the research on the chronology of the four-times ice age is far from enough. The Shaluli Mountai...It is generally considered that four-times ice age happened during the Quaternary epoch on the Tibetan Plateau. However, the research on the chronology of the four-times ice age is far from enough. The Shaluli Mountain on the Southeastern Tibetan Plateau is an ideal place for plaeo-glacier study, because there are abundant Quaternary glacial remains there. This paper discusses the ages of the Quaternary glaciations, based on the exposure dating of roche moutonnée, moraines and gla- cial erosion surfaces using in situ cosmogenic isotopes 10Be. It is found that the exposure age of the roche moutonnée at Tuershan is 15 ka, corresponding to Stage 2 of the deep-sea oxygen isotope, suggesting that the roche moutonnée at Tuershan is formed in the last glacial maximum. The expo- sure age of glacial erosion surface at Laolinkou is 130―160 ka, corresponding to Stage 6 of the deep-sea oxygen isotope. The oldest end moraine at Kuzhaori may form at 421―766 kaBP, corre- sponding to Stages 12―18 of the deep-sea oxygen isotope. In accordance with the climate charac- teristic of stages 12,14,16 and 18 reflected by the deep-sea oxygen isotope, polar ice cores and loess sequence, the oldest end moraine at Kuzhaori may form at stage 12 or stage 16, the latter is more possible.展开更多
基金supported by Chinese National Natural Science Foundation (No. 51809016 and No. 51979152)Chongqing Municipal Natural Science Foundation (No. cstc2019jcyjmsxmX0645)
文摘A new blasting approach of combined blastholes with different diameters is proposed to solve the problems of oversize boulders and rock toes in open-pit mine. A non-ideal detonation model and a statistical damage constitutive model are implemented in dynamic finite element analysis to investigate the formation mechanism of oversize boulders and toes. The damage distribution and evolution process of rock blasting fragmentation is simulated, and the scheme is further optimized. Numerical analysis results showed that pocket charges and satellite blastholes can only improve bench top fragmentation, but they cannot reduce the oversize in the middle and bottom of bench as well as the toe problem. The new blasting approach of combined blastholes with different diameters can effectively reduce the oversize boulders and toes as well as the production costs.
基金supported by the National Natural Science Foundation of China(Grant No.51778273)。
文摘Concrete dams are reliable when subjected to static loads such as earth pressure and water pressure.However,the dam failure would be abrupt and catastrophic if it is impacted by boulders.This study simulated the dynamic response of flat dam,concave dam,and convex dam under the impact of boulders by using ANSYS/LS-DYNA finite element software.In the numerical simulation,the strain rate effect under the impact load is considered,and Holmquist-Johnson-Cook(HJC)model-a dynamic damage constitutive model is applied to concrete materials.Results show that the peak impact force of concave dam is minimum.Meanwhile,for different dam types(flat dam,concave dam,and convex dam)and impactor velocities(5,10,and 15 m/s),the impact force fluctuates with the height of the impact point and it reaches the maximum value when the height of the impact point is 2/3 of the dam height.Numerical simulation mainly considers different masses and velocities and obtains empirical formulae of impact force for three dam types.The established empirical formula for the flat dam is compared with the existing classical formula and several similar experimental tests.It was found that the newly empirical formulae are reasonable and effective,and it provides design suggestions for similar concrete dams.
文摘Boulder spacing in mountain rivers and near-wake flow zones within the boulder array is very useful for fish habitat and growth of aquatic organisms.The present study aims to investigate how the boulder array and spacing influence the near-bed flow structures in a gravel-bed stream.Boulders are staggered over a gravel-bed stream with three different inter-boulder spacing namely(a)large(b)medium and(c)small spacing.An acoustic Doppler velocimeter was used for flow measurements in a rectangular channel and the results were compared with those acquired from numerical simulation.The time-averaged velocity profiles at the near-wake flow zones of boulders experience maximum flow retardation which is an outcome of the boulder-induced form roughness.The ratio of velocity differences associated to form and skin roughness and its positive magnitude reveals the dominance of form roughness closest to the boulders.Form roughness computed is 1.75 to 2 times higher than the skin roughness at the near-wake flow region.In particular,the collective immobile boulders placed at different inter-boulder spacings developed high and low bed shear stresses closest to the boulders.The low bed shear stresses characterised by a secondary peak developed at the trough location of the boulders is attributed to the skin shear stress.Further,the spatial averaging of time-averaged flow quantities gives additional impetus to present an improved illustration of fluid shear stresses.The formation of form-induced shear stress is estimated to be 17%to 23%of doubleaveraged Reynolds shear stress and partially compensates for the damping of time-averaged Reynolds shear stress in the interfacial sub-layer.The quadrant analysis of spatial velocity fluctuations depicts that the form-induced shear stresses are dominant in the interfacial sub-layer and have no significance above the gravel-bed surface.
基金The National Natural Science Foundation of China under contract No.41930538the Scientific Research Foundation of the Third Institute of Oceanography,Ministry of Natural Resources under contract No.2019029.
文摘Extreme storm events in coastal zones play significant roles in shaping the morphology of boulder beaches.However,boulder displacement and the geomorphological evolution of boulder beaches driven by different extreme storm events,especially typhoon events,remain poorly understood.Thus,boulder displacement and the geomorphic response on a boulder beach in Fujian,southeastern China,were explored before,during and after a cold wave event(Dec.1–7,2020)and before and after Typhoon In-Fa(Jul.19–27,2021),a large tropical storm.This was achieved by tracking 42 tagged boulders distributed in the intertidal and supratidal zones using Radio Frequency Identification(RFID)and topographic surveys using real-time kinematic techniques,respectively.The results showed obvious disparities in boulder displacement in different geomorphic zones due to cold wave and typhoon events that were mainly characterized by migration magnitude,range,direction,and mode of transport.The typhoon event led to rapid and substantial changes in the overall morphology of the boulder beach,while the cold wave event impacted the intertidal morphology of the boulder beach to only a small extent.The surrounding structure of boulders,beach slope and beach elevation had a combined dominant effect on boulder displacement under the same extreme event.Hydrodynamic factors(effective wave energy fluxes,incident wave direction,storm surge and water level)had dominant effects on boulder displacement during different extreme events.In terms of a single event,the magnitude of the boulder displacement driven by the typhoon was much greater than that driven by the cold wave.However,considering the frequency and duration of cold waves in winter,the impact of multiple consecutive cold waves on the geomorphology of the boulder beach cannot be ignored in this study area.Alternating and repeated interactions between these two processes constitute the complete geomorphic evolution of the boulder beach.This study contributes to improved predictions of the morphodynamic response of boulder beaches to future storms,especially large tropical storms,and facilitates better coastal management.
文摘This paper presents results from preliminary assessments in Ngasamo ward, Busega district in Simiyu region. The main objective was to assess cultural heritage assets in some areas of Bariadi district in Simiyu region. Specific objectives of the assessment are to identify tangible cultural heritage resources in Simiyu region;to identify intangible cultural heritage resources in Simiyu region;and to provide suggestions for pertinent protection, conservation and presentation of cultural heritage resources. The assessment was carried out through surveys that included documentation together with records for Global Positioning System (GPS) coordinates per surveyed locality;key informant interviews;and Focus Group Discussion. Results from the assessment revealed several worship areas that include immovable physical objects associated to ritual performance places. For example, wells like Luhuhi in Ilula village, Nkindwa biye tree in Ilula village, Magahi well in Isenge village, Isangijo hill at Isenge village, Dutwa well in Isenge village, Nyabusalu well in Igalukilo village and similar others are worship places that were revealed by informants. The assessment uncovered granite rock boulders that are being chopped off flakes for traditional medicine use in the area. Some cultural heritage sites have been identified such that a lot more needs to be explored in order to establish existence of other physical cultural heritage sites in Busega district, Bariadi district. For example, the grinding hollows, bao and the like are unique heritage resources. Such resources including undiscovered immovable archaeological objects would need presentation of sustainable preservation as well as conservation plans in line with Antiquities Acts, Antiquities Rules and Monuments of 1980 together with Cultural Heritage Policy of 2008.
基金supported by the project of Science & Technology Department of Sichuan Province (Grand No: 2015JY0235)National Natural Science Foundation of China (Grand No: 51509174)the Science and Technology Service Network Initiative (No. KFJ-SW-STS-180)
文摘The impact effect of boulder within debris flow is the key factor contributing to peak impact as well as to the failure of debris flow control work. So accurate measuring and calculating the impact force of debris flow can ensure the engineering design strength. However, limited to the existing laboratory conditions and piezoelectric sensor performance, it is impossible, based on the conventional measurements, to devise a computing method for expressing a reliable boulder impact force. This paper has therefore designed a new measurement device according to the method of integrating Fiber Bragg grating(FBG) and reinforced concrete composite beam(RCB) for measuring the impact force of debris flows, i.e. mounting FBG on the axially stressed steel bar in the composite beam at regular intervals to monitor the steel strain. RCB plays the role of contacting debris flow and protecting FBG sensors. Taking this new device as the experimental object, drop testing is designed for simulating and reflecting the boulder impact force. In a series of impacting tests, the relationship between the peak dynamic strain value of the steel bar and the impact force is analyzed, and based on which, an inversion model that uses the steel bar strain as the independent variable is established for calculating the boulder impact force.The experimental results show that this new inversion model can determine the impact force value and its acting position with a system error of 18.1%, which can provide an experimental foundation for measuring the impact force of boulders within the debris flow by the new FBG-based device.
基金supported by the National Natural Science Foundation of China (Grant Nos. 41861134008 and 41601476)the National Key Research and Development Program of China (Grant No. 2018YFC1505202)the 135 Strategic Program of the IMHE, CAS (Grant No. SDS-1351705)
文摘Loose deposits, rainfall and topography are three key factors that triggering debris flows.However, few studies have investigated the effects of loose deposits on the whole debris flow process.On June 28, 2012, a catastrophic debris flow occurred in the Aizi Valley, resulting in 40 deaths.The Aizi Valley is located in the Lower Jinsha River,southwestern Sichuan Province, China. The Aizi Valley debris flow has been selected as a case for addressing loose deposits effects on the whole debris flow process through remote sensing, field investigation and field experiments. Remote sensing interpretation and laboratory experiments were used to obtain the distribution and characteristics of the loose deposits, respectively. A field experiment was conducted to explore the mechanics of slope debris flows, and another field investigation was conducted to obtain the processes of debris flow formation, movement and amplification. The results showed that loose deposits preparation, slope debris flow initiation,gully debris flow confluence and valley debris flow amplification were dominated by the loose deposits.Antecedent droughts and earthquake activities may have increased the potential for loose soil sources in the Aizi Valley, which laid the foundation for debris flow formation. Slope debris flow initiated under rainfall, and the increase in the water content as well as the pore water pressure of the loose deposits were the key factors affecting slope failure. The nine gully debris flows converged in the valley, and the peak discharge was amplified 3.3 times due to a blockage and outburst caused by a large boulder. The results may help in predicting and assessing regional debris flows in dry-hot and seismic-prone areas based on loose deposits, especially considering large boulders.
文摘The cover photo shows a big granite boulder named 'Anvil Stone', which is about 10 m high and is perching on another boulder. As its name suggests, the 'Anvil Stone' looks like an anvil due to its inward concave sidewalls. The 'Anvil Stone' is located on a mountainous ridge of the Little Sangpu Mountain of eastern Guangdong, China at approximately 93 m above sea level. The mountain opposite the 'Anvil Stone' in the photo is the Great Sangpu Mountain. The plain between the Great and Little mountains represent a faulty depression formed by Dongshanhu fault.
文摘The interlayer structure of braid river reservoirs is complex and the interwell prediction is difficult in offshore oil field. Taking CFD11-1 oilfield of NgⅢ sand as an example, based on layer contrasting, the interlayer is divided into muddy interlayer, clay boulder interlayer, and physical interlayer according to lithology. Under the guidance of sedimentary model, we use the geology statistical inversion method to predict the clay boulder interlayer, consistent with the dynamic characteristics of oil production which is used for the prior quality control. The results of this study can objectively reveal the characteristics of interlayer space distribution. Compared with the traditional multi-well comparison and stochastic simulation model, this method is applied to the offshore oil field which is character with wide well space, sparse well network, which has very high application value in predicting the interlayer and deploying of inter-well encryption in the similar oilfield.
文摘Boulders and cobbles are often used in stream restoration projects to increase flow resistance and enhance channel stability and habitat diversity. Particle size metrics determined from the particle distribution are often used as a proxy for shear stress in field equations. Clustering of large particles has been thought to contribute to shear stress, but the effect of clustering is not accounted for in equations that use a representative particle size, such as the <em>D</em><sub>84</sub>. In this paper, clustering is defined using the upper tail (≥84%) in a variable called Topsum. The number of clusters, average size of clusters, and shear stress are evaluated using the proposed definition of cluster. Findings suggest that the upper tail represents the roughness height better than the commonly used proxy of <em>D</em><sub>84</sub> for boulder bed streams (streams which have a D84 particle 0.05 - 0.15 meters).
基金This study was supported by the National Key Basic Research Development Planning Project(Grant No.2003CB415201)the National Natural Science Foundation of China(Grant No.40572097)the Foundation for the Excellent Young Teachers from the National Education Administration(Grant No.2001BC12).
文摘It is generally considered that four-times ice age happened during the Quaternary epoch on the Tibetan Plateau. However, the research on the chronology of the four-times ice age is far from enough. The Shaluli Mountain on the Southeastern Tibetan Plateau is an ideal place for plaeo-glacier study, because there are abundant Quaternary glacial remains there. This paper discusses the ages of the Quaternary glaciations, based on the exposure dating of roche moutonnée, moraines and gla- cial erosion surfaces using in situ cosmogenic isotopes 10Be. It is found that the exposure age of the roche moutonnée at Tuershan is 15 ka, corresponding to Stage 2 of the deep-sea oxygen isotope, suggesting that the roche moutonnée at Tuershan is formed in the last glacial maximum. The expo- sure age of glacial erosion surface at Laolinkou is 130―160 ka, corresponding to Stage 6 of the deep-sea oxygen isotope. The oldest end moraine at Kuzhaori may form at 421―766 kaBP, corre- sponding to Stages 12―18 of the deep-sea oxygen isotope. In accordance with the climate charac- teristic of stages 12,14,16 and 18 reflected by the deep-sea oxygen isotope, polar ice cores and loess sequence, the oldest end moraine at Kuzhaori may form at stage 12 or stage 16, the latter is more possible.
