The boulder impact force in debris flow is generally calculated by static methods such as the cantilever beam models.However,these methods cannot describe the dynamic scenario of boulder collision on structures,so the...The boulder impact force in debris flow is generally calculated by static methods such as the cantilever beam models.However,these methods cannot describe the dynamic scenario of boulder collision on structures,so the inertia and damping effects of the structures are not involved causing an overestimation on the boulder impact force.In order to address this issue,a dynamic-based model for calculating the boulder impact force of a debris flow was proposed in this study,and the dynamic characteristics of a cantilever beam with multiple degrees of freedom under boulder collision were investigated.By using the drop-weight method to simulate boulders within debris flow,seven experiments of drop-weight impacting the cantilever beam were used to calibrate the error of the dynamicbased model.Results indicate that the dynamic-based model is able to reconstruct the impact force history on the cantilever beam during impact time and the error of dynamic-based model is 15.3%in calculating boulder impact force,significantly outperforming the cantilever beam model’s error of 285%.Therefore,the dynamic-based model can overcome the drawbacks of the static-based models and provide a more reliable theoretical foundation for the engineering design of debris flow control structures.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
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
In mountainous areas, geological disasters carrying large boulders can cause severe damage to the widely used masonry buildings due to the high impact forces. To better understand the damage of brick masonry buildings...In mountainous areas, geological disasters carrying large boulders can cause severe damage to the widely used masonry buildings due to the high impact forces. To better understand the damage of brick masonry buildings under the impact of boulders, a "block-joint" model is developed using threedimensional discontinuous deformation analysis(3-D DDA) to simulate the behaviour of the "brick-mortar" structure. The "block-joint" model is used to capture not only the large displacement and deformation of individual bricks but also the large-scale sliding and opening along the mortar between the bricks. The linear elastic constitutive model is applied to account for the non-plastic deformation behaviour of brick materials. Furthermore, the mechanical characteristics of the mortar are represented using the Mohr-Coulomb and Drucker-Prager criteria. To propose safe structural design schemes and effective reinforcement for brick masonry buildings, seven construction techniques are considered, includingdifferent grades of brick and mortar, effective shear areas and reinforced members. The proposed 3-D DDA model is used to analyse the velocity distribution and the key point displacements of the brick masonry building under the impact of boulders. The results show that upgrading the brick and mortar, increasing the wall thickness, making full use of the wall thickness, and adding a circular beam and structural column are very effective approaches for improving the impact resistance of brick masonry buildings.展开更多
Arrays of large immobile boulders,which are often encountered in steep mountain streams,affect the timing and magnitude of sediment transport events through their interactions with the approach flow.Despite their impo...Arrays of large immobile boulders,which are often encountered in steep mountain streams,affect the timing and magnitude of sediment transport events through their interactions with the approach flow.Despite their importance in the quantification of the bedload rate,the collective influence of a boulder array on the approach timeaveraged and turbulent flow field has to date been overlooked.The overarching objective is,thus,to assess the collective effects of a boulder array on the time-averaged and turbulent flow fields surrounding an individual boulder within the array,placing particular emphasis on highlighting the bed shear stress spatial variability.The objective of this study is pursued by resolving and comparing the timeaveraged and turbulent flow fields developing around a boulder,with and without an array of isolated boulders being present.The results show that the effects of an individual boulder on the time-averaged streamwise velocity and turbulence intensity were limited to the boulder's immediate vicinity in the streamwise(x/d c < 2-3) and vertical(z/d c < 1) directions.Outside of the boulder's immediate vicinity,the time-averaged streamwise velocity was found to be globally decelerated.This global deceleration was attributed to the form drag generated collectively by the boulder array.More importantly,the boulder array reduced the applied shear stress exerted on theindividual boulders found within the array,by absorbing a portion of the total applied shear.Furthermore,the array was found to have a "homogenizing" effect on the near-bed turbulence thus significantly reducing the turbulence intensity in the near-bed region.The findings of this study suggest that the collective boulder array bears a portion of the total applied bed shear stress as form drag,hence reducing the available bed shear stress for transporting incoming mobile sediment.Thus,the effects of the boulder array should not be ignored in sediment transport predictions.These effects are encapsulated in this study by Equation(6).展开更多
The most important objective of blasting in open pit mines is rock fragmentation.Prediction of produced boulders(oversized crushed rocks) is a key parameter in designing blast patterns.In this study,the amount of boul...The most important objective of blasting in open pit mines is rock fragmentation.Prediction of produced boulders(oversized crushed rocks) is a key parameter in designing blast patterns.In this study,the amount of boulder produced in blasting operations of Golegohar iron ore open pit mine,Iran was predicted via multiple regression method and artificial neural networks.Results of 33 blasts in the mine were collected for modeling.Input variables were:joints spacing,density and uniaxial compressive strength of the intact rock,burden,spacing,stemming,bench height to burden ratio,and specific charge.The dependent variable was ratio of boulder volume to pattern volume.Both techniques were successful in predicting the ratio.In this study,the multiple regression method was superior with coefficient of determination and root mean squared error values of 0.89 and 0.19,respectively.展开更多
Boulder block ramps are river engineering structures used to stabilise river beds. Block ramps provide a semi-natural and aesthetically pleasing solution to certain river engineering problems in mountain streams. When...Boulder block ramps are river engineering structures used to stabilise river beds. Block ramps provide a semi-natural and aesthetically pleasing solution to certain river engineering problems in mountain streams. When constructing block ramps,one can use the dissipative behaviour of large macroroughness elements randomly placed on the river bed to enhance fish migration in an upstream direction thus, in this sense, meeting the requirements of the EU Water Framework Directive. Block ramps are often designed and constructed to replace damaged drop hydraulic structures in the channels of mountain streams. This paper investigates the resilience of a particular block ramp placed in the Krzczonówka stream(Polish Carpathians) in terms of the engineering design function and its durability against damaging. A hydrodynamic analysis of a block ramp is presented before and after a flood event that changed the configuration of the blocks. The seminatural unstructured hydraulic structure was built on the Krzczonowka stream to protect gas pipes which are located beneath it. As a result of several floods, the boulder block chute described in this paper was damaged, and some boulders were dislodged and transported downstream. Our post-flood investigations of bathymetry and velocity revealed that even damaged boulder blocks, removed from the chute and displaced downstream of the structure, still provide significant energy dissipation of the flowing water. The novel of our paper is for the first time showing very detailed analysis of unstructured block ramp hydrodynamics parameters done in the field.Also the novel finding of our investigations shows that before and after the flood event the unstructured block ramp structure, is still fish friendly in terms of hydrodynamics.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
Excessive sedimentation in mountain stream ecosystems is a critical environmental problem due to the clogging of streambeds by sediment particles within the hyporheic zone,with detrimental effects on fish spawning hab...Excessive sedimentation in mountain stream ecosystems is a critical environmental problem due to the clogging of streambeds by sediment particles within the hyporheic zone,with detrimental effects on fish spawning habitat.In this research,the effects of an array of boulders in regulating the intrusion of incoming sand within a gravel substrate were evaluated by performing detailed experiments in a laboratory flume.A unique experimental setup and two different sampling techniques were utilized for measuring the infiltrated sand within the gravel bed under two bed shear stress conditions(moderate vs.high).For comparison purposes,experiments were performed without and with the presence of partially submerged to the flow(protruding) boulders,which is typical for the average flow conditions found in mountain streams.Results indicated that sand infiltrated primarily in the upper part of the gravel bed creating a surface seal which hindered the penetration of sand particles deeper into the bed.An exponential decrease of the amount of the infiltrated sand within the hyporheic zone was observed in all experiments regardless of the presence of boulders.However,the presence of boulders promoted sediment intrusion of sand particles especially for the moderate applied bed shear stress condition,since the total amount of the infiltrated sand was found to be on average 44% greater whenboulders were present.The findings from this study can provide additional insight regarding the role of boulders on promoting downwelling of flow and sediment within the gravel substrate with potential effects on fish habitat.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
The impacts of natural boulders carried by debris flows pose serious risks to the safety and reliability of structures and buildings.Natural boulders can be highly random and unpredictable.Consequently,boulder control...The impacts of natural boulders carried by debris flows pose serious risks to the safety and reliability of structures and buildings.Natural boulders can be highly random and unpredictable.Consequently,boulder control during debris flows is crucial but difficult.Herein,an eco-friendly control system featuring anchoring natural boulders(NBs)with(negative Poisson's ratio)NPR anchor cables is proposed to form an NB-NPR baffle.A series of flume experiments are conducted to verify the effect of NB-NPR baffles on controlling debris flow impact.The deployment of NB-NPR baffles substantially influences the kinematic behavior of a debris flow,primarily in the form of changes in the depositional properties and impact intensities.The results show that the NB-NPR baffle matrix successfully controls boulder mobility and exhibits positive feedback on solid particle deposition.The NB-NPR baffle group exhibits a reduction in peak impact force ranging from 29%to 79%compared to that of the control group in the basic experiment.The NPR anchor cables play a significant role in the NB-NPR baffle by demonstrating particular characteristics,including consistent resistance,large deformation,and substantial energy absorption.The NB-NPR baffle innovatively utilizes the natural boulders in a debris flow gully by converting destructive boulders into constructive boulders.Overall,this research serves as a basis for future field experiments and applications.展开更多
The area of the present investigation’s expanse constitutes the southernmost extent of the southeast Kumaun Himalaya and western Nepal Himalaya.Multidisciplinary approaches have been employed to understand the landfo...The area of the present investigation’s expanse constitutes the southernmost extent of the southeast Kumaun Himalaya and western Nepal Himalaya.Multidisciplinary approaches have been employed to understand the landforms associated with tectonic deformation,through detailed field investigation supplemented by the geodetic,chronological,and morphometric database.The morphogenic expressions of the Main Boundary Thrust(MBT)are reflected in the form of~25 km long E-W trending north dipping fault scarp.The deformation along the strike length of the Himalayan Frontal Thrust(HFT)is noticed in the form of uplifted and incised fill terraces,and strath terraces.The deformation within the fluvial sequences in the study area can be visualized in the form of sheared boulders and pebbles,tilted and faulted terrace deposits.Furthermore,the chronological data of fluvial landforms in the study area suggests two major phases of tectonic deformations that have occurred around 58.7±10.8 ka and 3.88±0.4 ka.The chronology of late-Quaternary landforms advocates that the initial stage of aggradations in the Himalayan foothills commenced around 75.1±0.58 ka.The aggradational landforms resulted from the diverse depositional regime as evident from the nature of the sediment sequences from clasts dominated to thick mud sequences.The rate of deformation in the southeastern Kumaun and western Nepal Himalaya is±7 mm/yr,as per the data obtained from the Persistent Scatterer Interferometric Synthetic Aperture Radar(PSInSAR).The landform deformation pattern,phase of incision and aggradation,frequent occurrence of landslides,and recent past earthquake activity within the wide zone of the HFT,the MBT,and Ramgarh Thrust suggests that the southernmost front of the Kumaun Himalaya is active and has potential for future geohazard.The foothill zone of Himalayan towns are actively growing in terms of population and infrastructural development.Therefore,such intradisciplinary studies for tectonically active regions are needed for future infrastructural development.展开更多
基金supported by the National Natural Science Foundation of China(U2244227)National Key R&D Program of China(2023YFC3007205)National Natural Science Foundation of China(No.42271013).
文摘The boulder impact force in debris flow is generally calculated by static methods such as the cantilever beam models.However,these methods cannot describe the dynamic scenario of boulder collision on structures,so the inertia and damping effects of the structures are not involved causing an overestimation on the boulder impact force.In order to address this issue,a dynamic-based model for calculating the boulder impact force of a debris flow was proposed in this study,and the dynamic characteristics of a cantilever beam with multiple degrees of freedom under boulder collision were investigated.By using the drop-weight method to simulate boulders within debris flow,seven experiments of drop-weight impacting the cantilever beam were used to calibrate the error of the dynamicbased model.Results indicate that the dynamic-based model is able to reconstruct the impact force history on the cantilever beam during impact time and the error of dynamic-based model is 15.3%in calculating boulder impact force,significantly outperforming the cantilever beam model’s error of 285%.Therefore,the dynamic-based model can overcome the drawbacks of the static-based models and provide a more reliable theoretical foundation for the engineering design of debris flow control structures.
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.
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sponsored by the National Science & Technology Pillar Programme of the Ministry of Science and Technology of China (Grant No. 2014BAL05B01)National Natural Science Foundation of China (Grant No. 51708420)+3 种基金Shanghai Pujiang Program (Grant No. 17PJ1409100)Natural Science Foundation of Shanghai (Grant No. 17ZR1432300)the Fundamental Research Funds for the Central Universities (Grant No. 2016KJ024)the Shanghai Peak Discipline Program for Higher Education Institutions (Class I)-Civil Engineering
文摘In mountainous areas, geological disasters carrying large boulders can cause severe damage to the widely used masonry buildings due to the high impact forces. To better understand the damage of brick masonry buildings under the impact of boulders, a "block-joint" model is developed using threedimensional discontinuous deformation analysis(3-D DDA) to simulate the behaviour of the "brick-mortar" structure. The "block-joint" model is used to capture not only the large displacement and deformation of individual bricks but also the large-scale sliding and opening along the mortar between the bricks. The linear elastic constitutive model is applied to account for the non-plastic deformation behaviour of brick materials. Furthermore, the mechanical characteristics of the mortar are represented using the Mohr-Coulomb and Drucker-Prager criteria. To propose safe structural design schemes and effective reinforcement for brick masonry buildings, seven construction techniques are considered, includingdifferent grades of brick and mortar, effective shear areas and reinforced members. The proposed 3-D DDA model is used to analyse the velocity distribution and the key point displacements of the brick masonry building under the impact of boulders. The results show that upgrading the brick and mortar, increasing the wall thickness, making full use of the wall thickness, and adding a circular beam and structural column are very effective approaches for improving the impact resistance of brick masonry buildings.
基金supported by the United States National Science Foundation (Grant No. CBET1033732)
文摘Arrays of large immobile boulders,which are often encountered in steep mountain streams,affect the timing and magnitude of sediment transport events through their interactions with the approach flow.Despite their importance in the quantification of the bedload rate,the collective influence of a boulder array on the approach timeaveraged and turbulent flow field has to date been overlooked.The overarching objective is,thus,to assess the collective effects of a boulder array on the time-averaged and turbulent flow fields surrounding an individual boulder within the array,placing particular emphasis on highlighting the bed shear stress spatial variability.The objective of this study is pursued by resolving and comparing the timeaveraged and turbulent flow fields developing around a boulder,with and without an array of isolated boulders being present.The results show that the effects of an individual boulder on the time-averaged streamwise velocity and turbulence intensity were limited to the boulder's immediate vicinity in the streamwise(x/d c < 2-3) and vertical(z/d c < 1) directions.Outside of the boulder's immediate vicinity,the time-averaged streamwise velocity was found to be globally decelerated.This global deceleration was attributed to the form drag generated collectively by the boulder array.More importantly,the boulder array reduced the applied shear stress exerted on theindividual boulders found within the array,by absorbing a portion of the total applied shear.Furthermore,the array was found to have a "homogenizing" effect on the near-bed turbulence thus significantly reducing the turbulence intensity in the near-bed region.The findings of this study suggest that the collective boulder array bears a portion of the total applied bed shear stress as form drag,hence reducing the available bed shear stress for transporting incoming mobile sediment.Thus,the effects of the boulder array should not be ignored in sediment transport predictions.These effects are encapsulated in this study by Equation(6).
文摘The most important objective of blasting in open pit mines is rock fragmentation.Prediction of produced boulders(oversized crushed rocks) is a key parameter in designing blast patterns.In this study,the amount of boulder produced in blasting operations of Golegohar iron ore open pit mine,Iran was predicted via multiple regression method and artificial neural networks.Results of 33 blasts in the mine were collected for modeling.Input variables were:joints spacing,density and uniaxial compressive strength of the intact rock,burden,spacing,stemming,bench height to burden ratio,and specific charge.The dependent variable was ratio of boulder volume to pattern volume.Both techniques were successful in predicting the ratio.In this study,the multiple regression method was superior with coefficient of determination and root mean squared error values of 0.89 and 0.19,respectively.
基金financed by the Ministry of Science and Higher Education of the Republic of Poland: 1. Cracow University of Technology, Faculty of Civil Engineering: L4/106/2018/DS, L4/107/2018/DS and L4/585/2018/DS-M. 2. University of Agriculture in Krakow: BM2313/KIWi G/2018
文摘Boulder block ramps are river engineering structures used to stabilise river beds. Block ramps provide a semi-natural and aesthetically pleasing solution to certain river engineering problems in mountain streams. When constructing block ramps,one can use the dissipative behaviour of large macroroughness elements randomly placed on the river bed to enhance fish migration in an upstream direction thus, in this sense, meeting the requirements of the EU Water Framework Directive. Block ramps are often designed and constructed to replace damaged drop hydraulic structures in the channels of mountain streams. This paper investigates the resilience of a particular block ramp placed in the Krzczonówka stream(Polish Carpathians) in terms of the engineering design function and its durability against damaging. A hydrodynamic analysis of a block ramp is presented before and after a flood event that changed the configuration of the blocks. The seminatural unstructured hydraulic structure was built on the Krzczonowka stream to protect gas pipes which are located beneath it. As a result of several floods, the boulder block chute described in this paper was damaged, and some boulders were dislodged and transported downstream. Our post-flood investigations of bathymetry and velocity revealed that even damaged boulder blocks, removed from the chute and displaced downstream of the structure, still provide significant energy dissipation of the flowing water. The novel of our paper is for the first time showing very detailed analysis of unstructured block ramp hydrodynamics parameters done in the field.Also the novel finding of our investigations shows that before and after the flood event the unstructured block ramp structure, is still fish friendly in terms of hydrodynamics.
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.
基金support provided by the NSF Hydroscience Division (Grant Nos. EAR-0208358, GEO-1419073, CBET-1033732)
文摘Excessive sedimentation in mountain stream ecosystems is a critical environmental problem due to the clogging of streambeds by sediment particles within the hyporheic zone,with detrimental effects on fish spawning habitat.In this research,the effects of an array of boulders in regulating the intrusion of incoming sand within a gravel substrate were evaluated by performing detailed experiments in a laboratory flume.A unique experimental setup and two different sampling techniques were utilized for measuring the infiltrated sand within the gravel bed under two bed shear stress conditions(moderate vs.high).For comparison purposes,experiments were performed without and with the presence of partially submerged to the flow(protruding) boulders,which is typical for the average flow conditions found in mountain streams.Results indicated that sand infiltrated primarily in the upper part of the gravel bed creating a surface seal which hindered the penetration of sand particles deeper into the bed.An exponential decrease of the amount of the infiltrated sand within the hyporheic zone was observed in all experiments regardless of the presence of boulders.However,the presence of boulders promoted sediment intrusion of sand particles especially for the moderate applied bed shear stress condition,since the total amount of the infiltrated sand was found to be on average 44% greater whenboulders were present.The findings from this study can provide additional insight regarding the role of boulders on promoting downwelling of flow and sediment within the gravel substrate with potential effects on fish habitat.
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financial support from the National Natural Science Foundation of China(Grant No.41941018).
文摘The impacts of natural boulders carried by debris flows pose serious risks to the safety and reliability of structures and buildings.Natural boulders can be highly random and unpredictable.Consequently,boulder control during debris flows is crucial but difficult.Herein,an eco-friendly control system featuring anchoring natural boulders(NBs)with(negative Poisson's ratio)NPR anchor cables is proposed to form an NB-NPR baffle.A series of flume experiments are conducted to verify the effect of NB-NPR baffles on controlling debris flow impact.The deployment of NB-NPR baffles substantially influences the kinematic behavior of a debris flow,primarily in the form of changes in the depositional properties and impact intensities.The results show that the NB-NPR baffle matrix successfully controls boulder mobility and exhibits positive feedback on solid particle deposition.The NB-NPR baffle group exhibits a reduction in peak impact force ranging from 29%to 79%compared to that of the control group in the basic experiment.The NPR anchor cables play a significant role in the NB-NPR baffle by demonstrating particular characteristics,including consistent resistance,large deformation,and substantial energy absorption.The NB-NPR baffle innovatively utilizes the natural boulders in a debris flow gully by converting destructive boulders into constructive boulders.Overall,this research serves as a basis for future field experiments and applications.
基金Council of Scientific and Innovative Research for providing fellowship (file number- 09/0420(15968)/2022-EMRI)
文摘The area of the present investigation’s expanse constitutes the southernmost extent of the southeast Kumaun Himalaya and western Nepal Himalaya.Multidisciplinary approaches have been employed to understand the landforms associated with tectonic deformation,through detailed field investigation supplemented by the geodetic,chronological,and morphometric database.The morphogenic expressions of the Main Boundary Thrust(MBT)are reflected in the form of~25 km long E-W trending north dipping fault scarp.The deformation along the strike length of the Himalayan Frontal Thrust(HFT)is noticed in the form of uplifted and incised fill terraces,and strath terraces.The deformation within the fluvial sequences in the study area can be visualized in the form of sheared boulders and pebbles,tilted and faulted terrace deposits.Furthermore,the chronological data of fluvial landforms in the study area suggests two major phases of tectonic deformations that have occurred around 58.7±10.8 ka and 3.88±0.4 ka.The chronology of late-Quaternary landforms advocates that the initial stage of aggradations in the Himalayan foothills commenced around 75.1±0.58 ka.The aggradational landforms resulted from the diverse depositional regime as evident from the nature of the sediment sequences from clasts dominated to thick mud sequences.The rate of deformation in the southeastern Kumaun and western Nepal Himalaya is±7 mm/yr,as per the data obtained from the Persistent Scatterer Interferometric Synthetic Aperture Radar(PSInSAR).The landform deformation pattern,phase of incision and aggradation,frequent occurrence of landslides,and recent past earthquake activity within the wide zone of the HFT,the MBT,and Ramgarh Thrust suggests that the southernmost front of the Kumaun Himalaya is active and has potential for future geohazard.The foothill zone of Himalayan towns are actively growing in terms of population and infrastructural development.Therefore,such intradisciplinary studies for tectonically active regions are needed for future infrastructural development.
