Estimation of unsaturated hydraulic conductivity could benefit many engineering or research problems such as water flow in the vadose zone, unsaturated seepage and capillary barriers for underground waste isolation. The unsaturated hydraulic conductivity of a soil is related to its saturated hydraulic conductivity value as well as its water retention behaviour. By following the first author's previous work, the saturated hydraulic conductivity and water retention curve (WRC) of sandy soils can be estimated from their basic gradation parameters. In this paper, we further suggest the applicable range of the estimation method is for soils with d 10 > 0.02 mm and C u < 20, in which d 10 is the grain diameter corresponding to 10% passing and C u is the coefficient of uniformity (C u = d 60 /d 10 ). The estimation method is also modified to consider the porosity variation effect. Then the proposed method is applied to predict unsaturated hydraulic conductivity properties of different sandy soils and also compared with laboratory and field test results. The comparison shows that the newly developed estimation method, which predicts the relative permeability of unsaturated sands from basic grain size parameters and porosity, generally has a fair agreement with measured data. It also indicates that the air-entry value is mainly relative to the mean grain size and porosity value change from the intrinsic value. The rate of permeability decline with suction is mainly associated with grain size polydispersity.
The glazed tile is an important building material used throughout the history of traditional Chinese architecture. Architectural glazed tiles used to decorate the screen walls of ancient China are studied scientifically for the first time. More than 30 glazed tile samples from the screen walls of the 15th to 18th century AD of the Hancheng Confucian Temple and Town God’s Temple in Shaanxi Province were carefully investigated using SEM–EDS and XRD. Microstructure and chemistry indicated the raw materials, the recipes and the technological choices used to produce the paste and glaze of the glazed tile samples studied. The causes for the key degradation processes of these glazed tiles used as building materials in the screen walls have also been discussed. This work has clear implications for the restoration and conservation treatments on these kinds of ancient Chinese building materials.
The mechanical behaviours of unsaturated soils are highly related to the water content and pore water and air distributions. Under the context of climate change, geo-disasters related to soil moisture change attract more and more research attentions. Due to the heterogeneity of soil textures and the complicated morphology of liquid phases, it is crucial to understand the microstructural features of unsaturated soils. This work presents a study based on a miniaturized suction controlled triaxial device which is suitable for micro-CT image analysis. A fine sand is sheared in this device under different suction levels while CT scans are taken at different strain stages. After image 3D reconstruction, image trinarization, label analysis, contact detection and other customized image analysis and calculations, the micro-mechanisms of unsaturated granular soils upon triaxial shearing are investigated. It is observed that the inter-particle contact coordination number is reduced after shearing due to the dilation behaviour and the sample with the highest capillary strength has the highest coordination number. Although there is an initial fabric anisotropy due to gravity and sample compaction, triaxial loading will further enlarge the fabric anisotropy of the solid phase and the solid fabric anisotropy is also associated with shear strength. With the development of shear band, water drains out and the quantity of small-volume liquid clusters in the liquid bridge increases. This shifts the distributions of inter-facial areas. The effective stress tensor is interpreted microscopically based on small RVEs. Based on the CT image analysis, the suction-induced stress component is not an isotropic term and the anisotropy of the water phase is increased with triaxial deformation as well as decrease in degree of saturation when there are more isolated water bridges formed around solid contacts.
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