Swelling and shrinkage due to moisture-change is one of the characteristics of the expansive soil,which is similar to the behavior of most materials under thermal effect,If the deformation is restricted,stress in expa...Swelling and shrinkage due to moisture-change is one of the characteristics of the expansive soil,which is similar to the behavior of most materials under thermal effect,If the deformation is restricted,stress in expansive soil is caused by the swell-shrinking.The stress is defined as "moisture-change stress" and is adopted to analyze swell-shrinkage deformation based on the elasticity mechanics theory.The state when the total stress becomes equal to the soil tensile strength is considered as the cracking criterion as moisture-change increases.Then,the initial cracking mechanism due to evaporation is revealed as follows:Different rates of moisture loss at different depths result in greater shrinkage deformation on the surface while there is smaller shrinkage deformation at the underlayer in expansive soil;cracks will grow when the nonuniform shrinkage deformation increases to a certain degree.A theoretical model is established,which may be used to calculate the stress caused by moisture-change.The depth of initial cracks growing is predicted by the proposed model in expansive soil,A series of laboratory tests are carried out by exposing expansive soil samples with different moisture-changes.The process of crack propagation is investigated by resistivity method.The test results show good consistency with the predicted results by the proposed theoretical model.展开更多
A contraction-expansion helical mixer which combines several features, viz. helical pipes for induction of secondary flows and sudden expansion and contraction array tor expansion vortices, has been designed to en- ha...A contraction-expansion helical mixer which combines several features, viz. helical pipes for induction of secondary flows and sudden expansion and contraction array tor expansion vortices, has been designed to en- hance flow mixing. A fast competitive-consecutive diazo coupling reaction is used to test the mixing efficiency of contraction-expansion helical mixer. Furthermore, an image processing technique is applied for data visualization and monitoring the extent of mixing. The mixing performance is found to be superior in comparison to the regular helical mixer in the range of Reynolds number from 170 to 1540. Moreover, the mixing time of contraction-expansion helical mixer was found to be reduced by more than 25% compared to the regular helical pipe. Finally, a simple correlation is proposed for predicting the mixing time.展开更多
In order to analyze the initial cracking behavior of highway embankment in the regions of expansive soil, the changes in peaks of tensile stress and their location on top of the embankment for a typical highway embank...In order to analyze the initial cracking behavior of highway embankment in the regions of expansive soil, the changes in peaks of tensile stress and their location on top of the embankment for a typical highway embankment section were simulated by ABAQUS. The simulation results indicate that the matric suction was a concave distribution on top of the expansive soil foundation and that it induced differential deformation of foundation and embankment. The peaks of tensile stress on top of the embankment are not located at a fixed site, but gradually move towards the shoulder following the evaporation duration. When the evaporation intensity is larger, the peak of tensile stress on top of embankment increases at a faster rate following the evaporation duration,and its location is closer to the shoulder. The thicker expansive soil layer helps the peaks of tensile stress to reach the critical tensile stress quickly, but the embankment cannot crack when the expansive soil layer is no more than 1.5m after 30d soil surface evaporation; the higher the embankment, the smaller the peak of tensile stress occurring on top of the highway embankment, and its location will be further away from the shoulder. Therefore, a higher embankment constructed on a thinner expansive soil layer can reduce the crack generation within the highway embankment.展开更多
基金Project(2006BAB04A10) supported by the National Science and Technology Pillar Program during the 11th Five Year Plan of ChinaProject(51008117) supported by the National Natural Science Foundation of China
文摘Swelling and shrinkage due to moisture-change is one of the characteristics of the expansive soil,which is similar to the behavior of most materials under thermal effect,If the deformation is restricted,stress in expansive soil is caused by the swell-shrinking.The stress is defined as "moisture-change stress" and is adopted to analyze swell-shrinkage deformation based on the elasticity mechanics theory.The state when the total stress becomes equal to the soil tensile strength is considered as the cracking criterion as moisture-change increases.Then,the initial cracking mechanism due to evaporation is revealed as follows:Different rates of moisture loss at different depths result in greater shrinkage deformation on the surface while there is smaller shrinkage deformation at the underlayer in expansive soil;cracks will grow when the nonuniform shrinkage deformation increases to a certain degree.A theoretical model is established,which may be used to calculate the stress caused by moisture-change.The depth of initial cracks growing is predicted by the proposed model in expansive soil,A series of laboratory tests are carried out by exposing expansive soil samples with different moisture-changes.The process of crack propagation is investigated by resistivity method.The test results show good consistency with the predicted results by the proposed theoretical model.
基金Supported by the National Key Technology R&D Program(2011BAE07B01)the National Natural Science Foundation of China(20836001)
文摘A contraction-expansion helical mixer which combines several features, viz. helical pipes for induction of secondary flows and sudden expansion and contraction array tor expansion vortices, has been designed to en- hance flow mixing. A fast competitive-consecutive diazo coupling reaction is used to test the mixing efficiency of contraction-expansion helical mixer. Furthermore, an image processing technique is applied for data visualization and monitoring the extent of mixing. The mixing performance is found to be superior in comparison to the regular helical mixer in the range of Reynolds number from 170 to 1540. Moreover, the mixing time of contraction-expansion helical mixer was found to be reduced by more than 25% compared to the regular helical pipe. Finally, a simple correlation is proposed for predicting the mixing time.
基金The National Natural Science Foundation of China(No.51378121)
文摘In order to analyze the initial cracking behavior of highway embankment in the regions of expansive soil, the changes in peaks of tensile stress and their location on top of the embankment for a typical highway embankment section were simulated by ABAQUS. The simulation results indicate that the matric suction was a concave distribution on top of the expansive soil foundation and that it induced differential deformation of foundation and embankment. The peaks of tensile stress on top of the embankment are not located at a fixed site, but gradually move towards the shoulder following the evaporation duration. When the evaporation intensity is larger, the peak of tensile stress on top of embankment increases at a faster rate following the evaporation duration,and its location is closer to the shoulder. The thicker expansive soil layer helps the peaks of tensile stress to reach the critical tensile stress quickly, but the embankment cannot crack when the expansive soil layer is no more than 1.5m after 30d soil surface evaporation; the higher the embankment, the smaller the peak of tensile stress occurring on top of the highway embankment, and its location will be further away from the shoulder. Therefore, a higher embankment constructed on a thinner expansive soil layer can reduce the crack generation within the highway embankment.
