The spatial variations of the soil hydraulic properties were mainly considered in vertical direction. The objectives of this study were to measure water-retention curves, θ（ψ）, and unsaturated hydraulic conductivi...The spatial variations of the soil hydraulic properties were mainly considered in vertical direction. The objectives of this study were to measure water-retention curves, θ（ψ）, and unsaturated hydraulic conductivity functions, K（ψ）, of the soils sampled at different slope positions in three directions, namely, in vertical direction, along the slope and along the contour, and to determine the effects of sampling direction and slope position of two soil catenas. At the upper slope positions, the surface soils （0-10 cm） sampled in the vertical direction had a lower soil water content, 0, at a certain soil water potential （-1 500 kPa 〈 ψ 〈 -10 kPa） and had the greatest unsaturated hydraulic conductivity, K, at ψ 〉 -10 kPa. At the lower slope positions, K at ψ〉 -10 kPa was smaller in the vertical direction than in the direction along the slope. The deep soils （100 110 cm） had similar soil hydraulic properties in all the three directions. The anisotropic variations of the hydraulic properties of the surface soils were ascribed to the effects of natural wetting and drying cycles on the structural heterogeneity. These results suggested that the anisotropy of soil hydraulic properties might be significant in influencing soil water movement along the slope and need to be considered in modeling.展开更多
A laboratory salt-water dynamics experiment using unsaturated soils in packed silt loam and clay soil columns withdifferent soil texture profiles and groundwater levels under crops were conducted to study the changes ...A laboratory salt-water dynamics experiment using unsaturated soils in packed silt loam and clay soil columns withdifferent soil texture profiles and groundwater levels under crops were conducted to study the changes of salt-waterdynamics induced by water uptake of crops and to propose the theoretical basis for the regulation and control of salt-water dynamics as well as to predict salinity levels. The HYDRUS 1D model was applied to simulate the one-dimensionalmovement of water and salt transport in the soil columns. The results showed that the salts mainly accumulated in theplow layer in the soil columns under crops. Soil water and salt both moved towards the plow layer due to soil waterabsorption by the crop root system. The salt contents in the column with lower groundwater were mostly greater thanthose with high groundwater. The water contents in the soil columns increased from top to the bottom due to plant rootwater uptake. The changes in groundwater level had little influence on water content of the root zone in the soil columnswith crop planting. Comparison between the simulated and the determined values showed that model simulation resultswere ideal, so it is practicable to do numerical simulation of soil salt and water transport by the HYDRUS 1D model.Furthermore, if the actual movement of salt and water in fields is to be described in detail, much work needs to be done.The most important thing is to refine the parameters and select precise boundary conditions.展开更多
The expansion and contraction of an open-graded friction course(OGFC)with a nominal maximum aggregate size of 13.2 mm(OGFC-13)with three air void contents(AVCs)and six saturation degrees(SDs)exposed to freeze-thaw(FT)...The expansion and contraction of an open-graded friction course(OGFC)with a nominal maximum aggregate size of 13.2 mm(OGFC-13)with three air void contents(AVCs)and six saturation degrees(SDs)exposed to freeze-thaw(FT)cycles were measured using strain gauges.Cantabro tests were conducted on OGFC-13 specimens before and after FT cycles to evaluate the degradation of raveling resistance.The effects of SD,AVC,and the number of FT cycles on the expansion and contraction of OGFC-13 and degradation of raveling resistance were analyzed.Results show that OGFC with low water saturation will contract to stability during the freezing process,whereas fully saturated OGFC will contract first and then expand to be stable.OGFC with a medium saturation experienced three stages,namely,contraction,expansion,and contraction,during the freezing process.For the OGFC with a low SD,the decrease in the void content can effectively reduce the low temperature shrinkage.By contrast,for the OGFC with a high SD,lower void content produces more temperature shrinkage at the beginning of freezing and less expansion at the end of freezing.The decreases in SD and AVC can effectively improve the raveling resistance of OGFCs exposed to FT cycles.展开更多
Pressure plate instrument is employed during drying, and unconfined compressive strength test is performed on the unsaturated specimen. Curves of shear force versus shear displacement, and curves of saturation degree ...Pressure plate instrument is employed during drying, and unconfined compressive strength test is performed on the unsaturated specimen. Curves of shear force versus shear displacement, and curves of saturation degree versus time are investigated. The results show that the specimens with similar curves of saturation degree versus time have nearly identical mechanical behavior. In particular, the uniform specimens should be chosen within the lower equilibrium saturation degree because steady test results are presented. Further, the conclusion is verified by the repeated test. Thus, the method for distinguishing the uniform unsaturated specimen is obtained. In the light of the method, an improved test process is proposed. The uniform specimens should be chosen by this method under the specific matric suction, and then shear tests are carried out on the chosen unsaturated specimen. Namely, initial value of unsaturated soil is not zero matric suction but a specific suction.展开更多
基金the National Natural Science Foundation of China (NSFC) (No40071044)the Deutsche Forschungsgemeinschaft (DFG) (NoZE 254/4)
文摘The spatial variations of the soil hydraulic properties were mainly considered in vertical direction. The objectives of this study were to measure water-retention curves, θ（ψ）, and unsaturated hydraulic conductivity functions, K（ψ）, of the soils sampled at different slope positions in three directions, namely, in vertical direction, along the slope and along the contour, and to determine the effects of sampling direction and slope position of two soil catenas. At the upper slope positions, the surface soils （0-10 cm） sampled in the vertical direction had a lower soil water content, 0, at a certain soil water potential （-1 500 kPa 〈 ψ 〈 -10 kPa） and had the greatest unsaturated hydraulic conductivity, K, at ψ 〉 -10 kPa. At the lower slope positions, K at ψ〉 -10 kPa was smaller in the vertical direction than in the direction along the slope. The deep soils （100 110 cm） had similar soil hydraulic properties in all the three directions. The anisotropic variations of the hydraulic properties of the surface soils were ascribed to the effects of natural wetting and drying cycles on the structural heterogeneity. These results suggested that the anisotropy of soil hydraulic properties might be significant in influencing soil water movement along the slope and need to be considered in modeling.
基金the National Key Basic Research Support Foundation (NKBRSF) of China (No. G1999011803),the National Natural Science Foundation of China (Nos. 40371058 and 40471018), the Jiangsu Provincial Society Deve-lopment Program of China (No. BS2003005), and the Institute of Geography and Limnology, Chinese Academy of Sciences(No. S250020).
文摘A laboratory salt-water dynamics experiment using unsaturated soils in packed silt loam and clay soil columns withdifferent soil texture profiles and groundwater levels under crops were conducted to study the changes of salt-waterdynamics induced by water uptake of crops and to propose the theoretical basis for the regulation and control of salt-water dynamics as well as to predict salinity levels. The HYDRUS 1D model was applied to simulate the one-dimensionalmovement of water and salt transport in the soil columns. The results showed that the salts mainly accumulated in theplow layer in the soil columns under crops. Soil water and salt both moved towards the plow layer due to soil waterabsorption by the crop root system. The salt contents in the column with lower groundwater were mostly greater thanthose with high groundwater. The water contents in the soil columns increased from top to the bottom due to plant rootwater uptake. The changes in groundwater level had little influence on water content of the root zone in the soil columnswith crop planting. Comparison between the simulated and the determined values showed that model simulation resultswere ideal, so it is practicable to do numerical simulation of soil salt and water transport by the HYDRUS 1D model.Furthermore, if the actual movement of salt and water in fields is to be described in detail, much work needs to be done.The most important thing is to refine the parameters and select precise boundary conditions.
基金The National Natural Science Foundation of China (No. 52178421)the Natural Science Foundation of Jiangsu Province(No. BK20191300)the Fundamental Research Funds for the Central Universities (No. B210202036)。
文摘The expansion and contraction of an open-graded friction course(OGFC)with a nominal maximum aggregate size of 13.2 mm(OGFC-13)with three air void contents(AVCs)and six saturation degrees(SDs)exposed to freeze-thaw(FT)cycles were measured using strain gauges.Cantabro tests were conducted on OGFC-13 specimens before and after FT cycles to evaluate the degradation of raveling resistance.The effects of SD,AVC,and the number of FT cycles on the expansion and contraction of OGFC-13 and degradation of raveling resistance were analyzed.Results show that OGFC with low water saturation will contract to stability during the freezing process,whereas fully saturated OGFC will contract first and then expand to be stable.OGFC with a medium saturation experienced three stages,namely,contraction,expansion,and contraction,during the freezing process.For the OGFC with a low SD,the decrease in the void content can effectively reduce the low temperature shrinkage.By contrast,for the OGFC with a high SD,lower void content produces more temperature shrinkage at the beginning of freezing and less expansion at the end of freezing.The decreases in SD and AVC can effectively improve the raveling resistance of OGFCs exposed to FT cycles.
基金Project(51179023) supported by the National Natural Science Foundation of China
文摘Pressure plate instrument is employed during drying, and unconfined compressive strength test is performed on the unsaturated specimen. Curves of shear force versus shear displacement, and curves of saturation degree versus time are investigated. The results show that the specimens with similar curves of saturation degree versus time have nearly identical mechanical behavior. In particular, the uniform specimens should be chosen within the lower equilibrium saturation degree because steady test results are presented. Further, the conclusion is verified by the repeated test. Thus, the method for distinguishing the uniform unsaturated specimen is obtained. In the light of the method, an improved test process is proposed. The uniform specimens should be chosen by this method under the specific matric suction, and then shear tests are carried out on the chosen unsaturated specimen. Namely, initial value of unsaturated soil is not zero matric suction but a specific suction.
