This article addresses where ruts are likely to occur during in-field forest operations. This was done by inspecting high-resolution surface images across New Brunswick (NB) and elsewhere to mark where ruts have (1) a...This article addresses where ruts are likely to occur during in-field forest operations. This was done by inspecting high-resolution surface images across New Brunswick (NB) and elsewhere to mark where ruts have (1) and have not (0) occurred in harvested cutblocks. This marking revealed 1) where off-road operations were likely done on moist to wet and unfrozen soils;and 2) whether the ruts so incurred were water-logged at the time of imaging. Through geospatial processing of the NB-wide digital elevation model (DEM, available at 1 m resolution), the following attributes were added to each of the marked rut and no-rut locations: 1) the cartographic depth-to-water (DTW) as referenced to the nearest flow channels with >1 and >4 ha upslope flow accumulation areas (FA);2) the topographic position index (TPI) in reference to the mean annulus elevation 50 m away from each DEM cell;3) mean slope and curvatures within each cell-surrounding 10-m circle;4) the terrain wetness index (TWI);5) soil association type according to the NB forest soil map, adjusted for NB’s most recent hydrographic network delineations for waterbodies and wetlands. Subjecting these data to logistic regression analysis revealed that image-located off-road rutting occurred at about 90% probability in water-accumulating zones where TPI is <0 m and DTW is <1 m. Using slope, curvature, TWI, and soil type as additional rut occurrence predictors did not affect this zonation significantly.展开更多
The rutting simulation method considering temperature variance and traffic time distribution is developed through ABAQUS software. The short-term behavior of pavement rut under the effects of temperature and traffic l...The rutting simulation method considering temperature variance and traffic time distribution is developed through ABAQUS software. The short-term behavior of pavement rut under the effects of temperature and traffic loading is addressed. Then sensitivity analysis on the factors of temperature and traffic loading is conducted and a short-term rutting prediction model is developed. The results show that under the same conditions of temperature and the number of load repetitions, rut increases sharply with the contact pressure in a linear manner, while as for the heavy load situation, the increases likely to be more nonlinear and faster; the significant factors affecting rutting include daily maximum air temperature, daily solar radiation volume, daily minimum air temperature, tire-pavement contact pressure and the number of load repetitions. Finally, a short-term rutting prediction model reflecting the effects of air temperature and traffic loading is developed, and it can be used for prediction and pre-waming for pavement rut prevention.展开更多
In order to make a scientific pavement maintenance decision, a grey-theory-based prediction methodological framework is proposed to predict pavement performance. Based on the field pavement rutting data,analysis of va...In order to make a scientific pavement maintenance decision, a grey-theory-based prediction methodological framework is proposed to predict pavement performance. Based on the field pavement rutting data,analysis of variance （ANOVA）was first used to study the influence of different factors on pavement rutting. Cluster analysis was then employed to investigate the rutting development trend.Based on the clustering results,the grey theory was applied to build pavement rutting models for each cluster, which can effectively reduce the complexity of the predictive model.The results show that axial load and asphalt binder type play important roles in rutting development.The prediction model is capable of capturing the uncertainty in the pavement performance prediction process and can meet the requirements of highway pavement maintenance,and,therefore,has a wide application prospects.展开更多
In order to investigate the permanent deformation behavior of asphalt mixtures from discontinuity, the virtual rutting test of asphalt mixtures is developed by the discrete element method （DEM）. A digital specimen g...In order to investigate the permanent deformation behavior of asphalt mixtures from discontinuity, the virtual rutting test of asphalt mixtures is developed by the discrete element method （DEM）. A digital specimen generation procedure considering aggregate gradation and irregular shape is developed based on the probability theory and the Monte Carlo method. The virtual rutting test is then conducted based on the generated digital specimen. In addition, on the basis of the time-temperature superposition （TTS） principle, a calculation method is used to reduce the computation time of the virtual rutting test. The simulation results are compared with the laboratory measurements. The results show that the calculation method based on the TFS principle in the discrete element （DE） viscoelastic model can significantly reduce the computation time. The deformation law of asphalt mixtures in the virtual rutting test is similar to the laboratory measurements, and the deformation and the dynamic stability of the virtual rutting test are slightly greater than the laboratory measurements. The two-dimensional virtual rutting test can predict the permanent deformation performance of asphalt mixtures.展开更多
In order to predict the long-term rutting of asphalt pavement, the effective temperature for pavement rutting is calculated using the numerical simulation method. The transient temperature field of asphalt pavement wa...In order to predict the long-term rutting of asphalt pavement, the effective temperature for pavement rutting is calculated using the numerical simulation method. The transient temperature field of asphalt pavement was simulated based on actual meteorological data of Nanjing. 24-hour rutting development under a transient temperature field was calculated in each month. The rutting depth accumulated under the static temperature field was also estimated and the relationship between constant temperature parameters was analyzed. Then the effective temperature for pavement rutting was determined based on the rutting equivalence principle. The results show that the monthly effective temperature is above 40 t in July and August, while in June and September it ranges from 30 to 40 Rutting development can be ignored when the monthly effective temperature is less than 30 t. The yearly effective temperature for rutting in Nanjing is around 38. 5 t. The long-term rutting prediction model based on the effective temperature can reflect the influences of meteorological factors and traffic time distribution.展开更多
文摘This article addresses where ruts are likely to occur during in-field forest operations. This was done by inspecting high-resolution surface images across New Brunswick (NB) and elsewhere to mark where ruts have (1) and have not (0) occurred in harvested cutblocks. This marking revealed 1) where off-road operations were likely done on moist to wet and unfrozen soils;and 2) whether the ruts so incurred were water-logged at the time of imaging. Through geospatial processing of the NB-wide digital elevation model (DEM, available at 1 m resolution), the following attributes were added to each of the marked rut and no-rut locations: 1) the cartographic depth-to-water (DTW) as referenced to the nearest flow channels with >1 and >4 ha upslope flow accumulation areas (FA);2) the topographic position index (TPI) in reference to the mean annulus elevation 50 m away from each DEM cell;3) mean slope and curvatures within each cell-surrounding 10-m circle;4) the terrain wetness index (TWI);5) soil association type according to the NB forest soil map, adjusted for NB’s most recent hydrographic network delineations for waterbodies and wetlands. Subjecting these data to logistic regression analysis revealed that image-located off-road rutting occurred at about 90% probability in water-accumulating zones where TPI is <0 m and DTW is <1 m. Using slope, curvature, TWI, and soil type as additional rut occurrence predictors did not affect this zonation significantly.
基金The National High Technology Research and Development Program of China (863 Program)(No.2006AA11Z110)
文摘The rutting simulation method considering temperature variance and traffic time distribution is developed through ABAQUS software. The short-term behavior of pavement rut under the effects of temperature and traffic loading is addressed. Then sensitivity analysis on the factors of temperature and traffic loading is conducted and a short-term rutting prediction model is developed. The results show that under the same conditions of temperature and the number of load repetitions, rut increases sharply with the contact pressure in a linear manner, while as for the heavy load situation, the increases likely to be more nonlinear and faster; the significant factors affecting rutting include daily maximum air temperature, daily solar radiation volume, daily minimum air temperature, tire-pavement contact pressure and the number of load repetitions. Finally, a short-term rutting prediction model reflecting the effects of air temperature and traffic loading is developed, and it can be used for prediction and pre-waming for pavement rut prevention.
基金The Major Scientific and Technological Special Project of Jiangsu Provincial Communications Department(No.2011Y/02-G1)
文摘In order to make a scientific pavement maintenance decision, a grey-theory-based prediction methodological framework is proposed to predict pavement performance. Based on the field pavement rutting data,analysis of variance （ANOVA）was first used to study the influence of different factors on pavement rutting. Cluster analysis was then employed to investigate the rutting development trend.Based on the clustering results,the grey theory was applied to build pavement rutting models for each cluster, which can effectively reduce the complexity of the predictive model.The results show that axial load and asphalt binder type play important roles in rutting development.The prediction model is capable of capturing the uncertainty in the pavement performance prediction process and can meet the requirements of highway pavement maintenance,and,therefore,has a wide application prospects.
基金The National Natural Science Foundation of China(No.51108081)
文摘In order to investigate the permanent deformation behavior of asphalt mixtures from discontinuity, the virtual rutting test of asphalt mixtures is developed by the discrete element method （DEM）. A digital specimen generation procedure considering aggregate gradation and irregular shape is developed based on the probability theory and the Monte Carlo method. The virtual rutting test is then conducted based on the generated digital specimen. In addition, on the basis of the time-temperature superposition （TTS） principle, a calculation method is used to reduce the computation time of the virtual rutting test. The simulation results are compared with the laboratory measurements. The results show that the calculation method based on the TFS principle in the discrete element （DE） viscoelastic model can significantly reduce the computation time. The deformation law of asphalt mixtures in the virtual rutting test is similar to the laboratory measurements, and the deformation and the dynamic stability of the virtual rutting test are slightly greater than the laboratory measurements. The two-dimensional virtual rutting test can predict the permanent deformation performance of asphalt mixtures.
基金The National Natural Science Foundation of China(No.51378121)the Fok Ying Tung Education Foundation(No.141076)the Scientific Innovation Research of College Graduates in Jiangsu Province(No.KYLX_0164)
文摘In order to predict the long-term rutting of asphalt pavement, the effective temperature for pavement rutting is calculated using the numerical simulation method. The transient temperature field of asphalt pavement was simulated based on actual meteorological data of Nanjing. 24-hour rutting development under a transient temperature field was calculated in each month. The rutting depth accumulated under the static temperature field was also estimated and the relationship between constant temperature parameters was analyzed. Then the effective temperature for pavement rutting was determined based on the rutting equivalence principle. The results show that the monthly effective temperature is above 40 t in July and August, while in June and September it ranges from 30 to 40 Rutting development can be ignored when the monthly effective temperature is less than 30 t. The yearly effective temperature for rutting in Nanjing is around 38. 5 t. The long-term rutting prediction model based on the effective temperature can reflect the influences of meteorological factors and traffic time distribution.
文摘目的 :评价目前临床上常用的两种诊断幽门螺杆菌 (HP)感染方法的敏感性、特异性。方法 :对 186例因消化道症状就医的老年患者行胃镜检查 ,同时行13 C 尿素呼气试验 ( 13 C UBT) ,快速尿素酶 (RUT)试验检查 ,用活检钳钳取胃窦黏膜组织行病理学检查。结果 :13 C UBT较RUT检查的敏感性、特异性高。结论 :13 C UBT和RUT具有安全、简便、可靠、无创的特点 ,是较好的HP检测方法 ,对于老年病人13 C
