An analytical solution is derived from the generalized governing equations of equal-strain consolidation with vertical drains under multi-ramp surcharge preloading. The hydraulic boundary conditions at both top and bo...An analytical solution is derived from the generalized governing equations of equal-strain consolidation with vertical drains under multi-ramp surcharge preloading. The hydraulic boundary conditions at both top and bottom of the consolidating soil are modelled as impeded drainage. The impeded drainage is described by using the third type boundary condition with a characteristic factor of drainage efficiency. Fully drained and undrained boundary conditions can also be modelled by applying an infinite and a zero characteristic factor, respectively. Simultaneous radial and vertical flow conditions are considered, together with the effects of drain resistance and smear. An increase in total stress due to multi-ramp loading is reasonably modelled as a function of both time and depth. A solution to calculate excess pore-water pressure at any arbitrary point in soil is derived, and the overall average degree of consolidation is obtained. It shows that the proposed solution can be used to analyze not only vertical-drain consolidation but also one-dimensional consolidation under either one-way or two-way vertical drainage conditions. The characteristic factors of drainage efficiency of top and bottom boundaries have a potentially important influence on consolidation. The boundary may be considered fully drained when the characteristic factor is greater than 100 and fully undrained when the characteristic factor is less than 0.1. The stress distribution along depth induced by the surcharge loading has a limited effect on the overall average degree of consolidation.展开更多
Porosity is one of the most important parameters for cement-based materials,which influences the mechanical property,transport property,and durability.The spatial and frequency distributions of local porosity of cemen...Porosity is one of the most important parameters for cement-based materials,which influences the mechanical property,transport property,and durability.The spatial and frequency distributions of local porosity of cement pastes are characterized using X-ray micro-tomography data and treating methods.The 3D spatial distributions for three cement paste specimens with different water cement(w/c)ratios show reasonable heterogeneity.The probability analysis also reveals this heterogeneity:the representative volume element(RVE)size based on porosity maps decreases with w/c ratio firstly,then increases with w/c ratio;and the heterogeneity on the characterized probe size or on the RVE size increases with w/c ratio.Average porosities obtained using the CT method are further compared with those by traditional methods.展开更多
Numerical simulations are carried out for gas-solid fluidized bed of cork particles, using discrete element method. Results exhibit the existence of a so-called anti core-annular porosity profile with lower porosity i...Numerical simulations are carried out for gas-solid fluidized bed of cork particles, using discrete element method. Results exhibit the existence of a so-called anti core-annular porosity profile with lower porosity in the core and higher porosity near the wall for non-slugging fluidization. The tendency to form this unfamiliar anti core-annular porosity profile is stronger when the solid flux is higher. There exist multiple inflection points in the simulated axial solid volume fraction profile for non-slugging fluidization. Results also show that the familiar core-annular porosity profile still appears for slugging fluidization. In addition, the classical choking phenomenon can be captured at the superficial gas velocity slightly lower than the correlated transport velocity.展开更多
基金Project(51278171)supported by the National Natural Science Foundation of ChinaProject(B13024)supported by Program of Introducing Talents of Discipline to Universities("111" Project),ChinaProject(2014B04914)supported by the Fundamental Research Funds for the Central Universities of China
文摘An analytical solution is derived from the generalized governing equations of equal-strain consolidation with vertical drains under multi-ramp surcharge preloading. The hydraulic boundary conditions at both top and bottom of the consolidating soil are modelled as impeded drainage. The impeded drainage is described by using the third type boundary condition with a characteristic factor of drainage efficiency. Fully drained and undrained boundary conditions can also be modelled by applying an infinite and a zero characteristic factor, respectively. Simultaneous radial and vertical flow conditions are considered, together with the effects of drain resistance and smear. An increase in total stress due to multi-ramp loading is reasonably modelled as a function of both time and depth. A solution to calculate excess pore-water pressure at any arbitrary point in soil is derived, and the overall average degree of consolidation is obtained. It shows that the proposed solution can be used to analyze not only vertical-drain consolidation but also one-dimensional consolidation under either one-way or two-way vertical drainage conditions. The characteristic factors of drainage efficiency of top and bottom boundaries have a potentially important influence on consolidation. The boundary may be considered fully drained when the characteristic factor is greater than 100 and fully undrained when the characteristic factor is less than 0.1. The stress distribution along depth induced by the surcharge loading has a limited effect on the overall average degree of consolidation.
基金supported by the National Natural Science Foundation of China(Grant No.51008072)the Fundamental Research Funds for the Central Universities(Grant No.2242014R30014)State Key Laboratory of High Performance Civil Engineering Materials(Grant No.2012CEM008)
文摘Porosity is one of the most important parameters for cement-based materials,which influences the mechanical property,transport property,and durability.The spatial and frequency distributions of local porosity of cement pastes are characterized using X-ray micro-tomography data and treating methods.The 3D spatial distributions for three cement paste specimens with different water cement(w/c)ratios show reasonable heterogeneity.The probability analysis also reveals this heterogeneity:the representative volume element(RVE)size based on porosity maps decreases with w/c ratio firstly,then increases with w/c ratio;and the heterogeneity on the characterized probe size or on the RVE size increases with w/c ratio.Average porosities obtained using the CT method are further compared with those by traditional methods.
基金supported by the National Natural Science Foundation of China(10871159)the Presidential Foundation of Gansu Normal University for Nationalities(201301)
文摘Numerical simulations are carried out for gas-solid fluidized bed of cork particles, using discrete element method. Results exhibit the existence of a so-called anti core-annular porosity profile with lower porosity in the core and higher porosity near the wall for non-slugging fluidization. The tendency to form this unfamiliar anti core-annular porosity profile is stronger when the solid flux is higher. There exist multiple inflection points in the simulated axial solid volume fraction profile for non-slugging fluidization. Results also show that the familiar core-annular porosity profile still appears for slugging fluidization. In addition, the classical choking phenomenon can be captured at the superficial gas velocity slightly lower than the correlated transport velocity.
