The decline in groundwater level is a key factor contributing to cover collapse in karst areas.In this study,the model tests and numerical simulations are conducted to reveal the breeding process and formation mechani...The decline in groundwater level is a key factor contributing to cover collapse in karst areas.In this study,the model tests and numerical simulations are conducted to reveal the breeding process and formation mechanism of cover collapse sinkholes caused by the decline of groundwater level in karst area.Firstly,the model tests confirm that the decline of groundwater level generates negative pressure at the lower edge of overlying soil.The negative pressure experiences four distinct phases during the groundwater drawdown process:rapid rise,slow decline,rapid decline,and gradual dissipation.The maximum negative pressure is influenced by the particle size distribution of the overlying soil.Then,the numerical simulations are carried out to investigate the change process of negative pressure caused by the loss of fillers in karst pipe.The simulated results indicate that the rate of groundwater decline and the thickness and initial void ratio of the overlying soil can affect the maximum negative pressure.As groundwater level drops,a negative pressure zone forms underground,causing tensile failure in the surrounding soil and creating an arched soil hole,which weakens the support for the overlying soil.This phenomenon can also lead to the collapse of the overlying soil under its self-weight.Groundwater table decline in karst areas can result in both internal and surface collapses.When the overlying soil is thin,internal and surface collapses occur simultaneously.In contrast,for thick overlying soil,internal collapse happens first,followed by a layer-by-layer collapse,ultimately forming sinkholes.Finally,the breeding process and formation mechanism of the Yujiawan Reservoir sinkholes are discussed.Geological conditions and groundwater level decline significantly affect internal collapse in karst areas,requiring careful consideration from on-site engineers.展开更多
Bio-embankment is an important soil and water conservation measure in the purple hilly area in China,which can effectively improve the ability of cultivated soil layers to resist rainfall erosion and runoff scour.In c...Bio-embankment is an important soil and water conservation measure in the purple hilly area in China,which can effectively improve the ability of cultivated soil layers to resist rainfall erosion and runoff scour.In contrast,the ecological effect of bioembankment depends on the stability of the earth bank.Taking the natural grass bank as a control(CK),the root distribution,root tensile properties and shear resistance of root-soil composites for 3 typical soil and water conservation bio-embankments,namely,Morus alba Linn(Morns),Zanthoxylum bungeanum Maxim(Zanthoxylum)and Medicago sativa(Medicago)were analysed.The results included the following:(1)The root system of the bio-embankments generally decreased in extent with the soil depth;fine roots in the o-io cm depth were most prevalent and significantly higher than those at the other depths,and coarse roots were mainly distributed in the o-30cm layer.(2)The stress-strain curves of the roots of each bio-embankment were single-peak curves without clear strain softening phenomena.The smaller the root diameters were,the smoother the stress-strain curves,and the lower the capability of the earth bank to resist collapse.The larger the root diameters were,the lower the tensile strength.The average root tensile force was highest for Zanthoxylum(73.91 N),followed by Medicago(68.07N)and Morus(61.88 N),and the average root tensile strength showed the same trend,16.52 MPa for Zanthoxylum,16.08 MPa for Medicago and 13.02MPa for Morus.(3)The bio-embankment measures significantly improved the soil shear resistance,especially under vertical loads of 1oo kPa and 200kPa.The soil internal friction angle showed a significant log-positive correlation with root morphological parameters of root length density(RLD),root surface area density(RSAD) and rootweight density(RWD),while the soil cohesion force showed a positive linear correlation with these parameters.The results provide effective parameters supporting for the design of bio-embankments and promoting the use of soil reinforcement with suitable species selection in protective earth banks for stability in the purple hilly area.展开更多
Self-excited oscillation in a collapsible tube is an important phenomenon in physiology. An experimental approach on self-excited oscillation in a thin-walled collapsi- ble tube is developed by using a high transmitta...Self-excited oscillation in a collapsible tube is an important phenomenon in physiology. An experimental approach on self-excited oscillation in a thin-walled collapsi- ble tube is developed by using a high transmittance and low Young＇s modulus silicone rubber tube. The elastic tube is manufactured by the method of centrifugal casting in our laboratory. An optical method for recording the evolution of the cross-sectional areas at a certain position along the longitudinal direction of the tube is developed based on the technology of refractive index matching. With the transparent tube, the tube law is measured under the static no-flow condition. The cross section at the middle position of the tube transfers from a quasi-circular configuration to an ellipse, and then to a dumbell-shape as the chamber pressure is increased. During the self-excited oscillation, two periodic self-excited oscillating states and one transitional oscillating state are identified. They all belong to the LU mode. These different oscillating states are related to the initial cross-sectional shape of the tube caused by the difference of the downstream transmural pressure.展开更多
The deformation fracture and stability of mountain under the earthquake action is an important issue that arouses concern of researchers in the field of engineering geology.The authors,from 2000 to 2006, selected the ...The deformation fracture and stability of mountain under the earthquake action is an important issue that arouses concern of researchers in the field of engineering geology.The authors,from 2000 to 2006, selected the 1933 earthquake in Diexi zone as a typical study site to carry out the genetic mechanism research of mountain deformation-fracture caused by earthquake; in order to have comparability,the breadth展开更多
Large-scale floods induced by dam failures could cause significant structural damage to buildings and massive loss of life.The coupling effect of large-scale flood spread and building collapse has complex impacts on t...Large-scale floods induced by dam failures could cause significant structural damage to buildings and massive loss of life.The coupling effect of large-scale flood spread and building collapse has complex impacts on the entire flow field,affecting flood risk assessment and building vulnerability evaluation.In this paper,a dynamic elevation change model designed to seamlessly interface with a structural vulnerability assessment model to investigate the interaction effect between floods and buildings is presented.The efficiency of the framework was validated by reconstructing the Gleno Dam-Break flood in Italy.Subsequently,a hydrodynamic model of the Jinsha-Yalong River that considers dynamic building collapse was established.The proposed model was compared with two traditional building treatment approaches and one that ignored the buildings.The results show that the interaction between the flood and buildings decreases the low-velocity area(below 1 m/s)by 7.44%-9.56%while increasing the high velocity area(above 4 m/s)by 10.71%-11.96%.Traditional and neglecting building treatments provide preliminary insights into densely built areas,and the latter could be an alternative for simplification because it can represent the worst-case scenario.Building collapse in response to large-scale floods typically occurs in four stages:flood spread,rapid expansion,gradual expansion,and flood recession.This analysis offers novel perspectives on flood prediction and simulations where the floodplain may contain buildings.This method could be useful for assessing structural vulnerability associated with large building stocks and developing flood mitigation strategies in densely populated areas.展开更多
基金supported by the Natural Science Foundation of Shandong Province,China(Grant No.ZR2020QE110)the National Natural Science Foundation of China,China(Grant No.52104089).
文摘The decline in groundwater level is a key factor contributing to cover collapse in karst areas.In this study,the model tests and numerical simulations are conducted to reveal the breeding process and formation mechanism of cover collapse sinkholes caused by the decline of groundwater level in karst area.Firstly,the model tests confirm that the decline of groundwater level generates negative pressure at the lower edge of overlying soil.The negative pressure experiences four distinct phases during the groundwater drawdown process:rapid rise,slow decline,rapid decline,and gradual dissipation.The maximum negative pressure is influenced by the particle size distribution of the overlying soil.Then,the numerical simulations are carried out to investigate the change process of negative pressure caused by the loss of fillers in karst pipe.The simulated results indicate that the rate of groundwater decline and the thickness and initial void ratio of the overlying soil can affect the maximum negative pressure.As groundwater level drops,a negative pressure zone forms underground,causing tensile failure in the surrounding soil and creating an arched soil hole,which weakens the support for the overlying soil.This phenomenon can also lead to the collapse of the overlying soil under its self-weight.Groundwater table decline in karst areas can result in both internal and surface collapses.When the overlying soil is thin,internal and surface collapses occur simultaneously.In contrast,for thick overlying soil,internal collapse happens first,followed by a layer-by-layer collapse,ultimately forming sinkholes.Finally,the breeding process and formation mechanism of the Yujiawan Reservoir sinkholes are discussed.Geological conditions and groundwater level decline significantly affect internal collapse in karst areas,requiring careful consideration from on-site engineers.
基金funded by the Natural Science Foundation of China (Grants No. 41771310)the Public welfare industry (agriculture) special research project (Grants No. 201503119-01-01).
文摘Bio-embankment is an important soil and water conservation measure in the purple hilly area in China,which can effectively improve the ability of cultivated soil layers to resist rainfall erosion and runoff scour.In contrast,the ecological effect of bioembankment depends on the stability of the earth bank.Taking the natural grass bank as a control(CK),the root distribution,root tensile properties and shear resistance of root-soil composites for 3 typical soil and water conservation bio-embankments,namely,Morus alba Linn(Morns),Zanthoxylum bungeanum Maxim(Zanthoxylum)and Medicago sativa(Medicago)were analysed.The results included the following:(1)The root system of the bio-embankments generally decreased in extent with the soil depth;fine roots in the o-io cm depth were most prevalent and significantly higher than those at the other depths,and coarse roots were mainly distributed in the o-30cm layer.(2)The stress-strain curves of the roots of each bio-embankment were single-peak curves without clear strain softening phenomena.The smaller the root diameters were,the smoother the stress-strain curves,and the lower the capability of the earth bank to resist collapse.The larger the root diameters were,the lower the tensile strength.The average root tensile force was highest for Zanthoxylum(73.91 N),followed by Medicago(68.07N)and Morus(61.88 N),and the average root tensile strength showed the same trend,16.52 MPa for Zanthoxylum,16.08 MPa for Medicago and 13.02MPa for Morus.(3)The bio-embankment measures significantly improved the soil shear resistance,especially under vertical loads of 1oo kPa and 200kPa.The soil internal friction angle showed a significant log-positive correlation with root morphological parameters of root length density(RLD),root surface area density(RSAD) and rootweight density(RWD),while the soil cohesion force showed a positive linear correlation with these parameters.The results provide effective parameters supporting for the design of bio-embankments and promoting the use of soil reinforcement with suitable species selection in protective earth banks for stability in the purple hilly area.
基金support from the National Nature Science Foundation of China (Grants 11372305 and 11002138)K.C. Wong Education Foundation for a Royal Society K.C. Wong Postdoctoral Fellowship
文摘Self-excited oscillation in a collapsible tube is an important phenomenon in physiology. An experimental approach on self-excited oscillation in a thin-walled collapsi- ble tube is developed by using a high transmittance and low Young＇s modulus silicone rubber tube. The elastic tube is manufactured by the method of centrifugal casting in our laboratory. An optical method for recording the evolution of the cross-sectional areas at a certain position along the longitudinal direction of the tube is developed based on the technology of refractive index matching. With the transparent tube, the tube law is measured under the static no-flow condition. The cross section at the middle position of the tube transfers from a quasi-circular configuration to an ellipse, and then to a dumbell-shape as the chamber pressure is increased. During the self-excited oscillation, two periodic self-excited oscillating states and one transitional oscillating state are identified. They all belong to the LU mode. These different oscillating states are related to the initial cross-sectional shape of the tube caused by the difference of the downstream transmural pressure.
文摘The deformation fracture and stability of mountain under the earthquake action is an important issue that arouses concern of researchers in the field of engineering geology.The authors,from 2000 to 2006, selected the 1933 earthquake in Diexi zone as a typical study site to carry out the genetic mechanism research of mountain deformation-fracture caused by earthquake; in order to have comparability,the breadth
基金supported by the National Natural Science Foundation of China(Grant No.52192671)the National Key Research and Development Program of China(Grant No.2022YFC3090600)+1 种基金the Research Fund of the State Key Laboratory of Simulation and Regulation of Water Cycle in River Basin(Grant No.SKL2022TS11)the Open Research Fund of Key Laboratory of River Basin Digital Twinning of Ministry of Water Resources(Grant No.Z0202042022)。
文摘Large-scale floods induced by dam failures could cause significant structural damage to buildings and massive loss of life.The coupling effect of large-scale flood spread and building collapse has complex impacts on the entire flow field,affecting flood risk assessment and building vulnerability evaluation.In this paper,a dynamic elevation change model designed to seamlessly interface with a structural vulnerability assessment model to investigate the interaction effect between floods and buildings is presented.The efficiency of the framework was validated by reconstructing the Gleno Dam-Break flood in Italy.Subsequently,a hydrodynamic model of the Jinsha-Yalong River that considers dynamic building collapse was established.The proposed model was compared with two traditional building treatment approaches and one that ignored the buildings.The results show that the interaction between the flood and buildings decreases the low-velocity area(below 1 m/s)by 7.44%-9.56%while increasing the high velocity area(above 4 m/s)by 10.71%-11.96%.Traditional and neglecting building treatments provide preliminary insights into densely built areas,and the latter could be an alternative for simplification because it can represent the worst-case scenario.Building collapse in response to large-scale floods typically occurs in four stages:flood spread,rapid expansion,gradual expansion,and flood recession.This analysis offers novel perspectives on flood prediction and simulations where the floodplain may contain buildings.This method could be useful for assessing structural vulnerability associated with large building stocks and developing flood mitigation strategies in densely populated areas.
