Soil moisture migration model based on Flux-concentration relation under steady rainfall

Moisture content distribution in soil is of great importance for understanding rainfall-induced slope failure and roadbed settlement. This study aims to develop a moisture migration model that improves the quantification of moisture content at an arbitrary point of the soil at any time for the whole process of infiltration under steady rainfall. The model was derived from the Richards' equation using the Flux-concentration relation, which was validated by numerical solutions calculated by Hydrus-1D software to evaluate the performance of the model. Results showed good accuracy and high adaptability for the moisture migration simulation of a wide range of soil types, and is applicable for short-duration and long-duration steady rainfall. Moreover, it can also reflect the stratification phenomenon for soil profile wetting by infiltration. Our analysis indicates that the flux and surface volumetric moisture content together can bound the boundary conditions of rainfall infiltration, which presents a shift from constant-flux to constant-concentration during a long-duration steady rainfall. The migration rate of the wetting front in the later stage of infiltration positively correlates with rainfall intensity under the constant-flux condition, while it finally stabilizes at Ks/(θs − θi) under the constant-concentration condition (i.e., Ks-saturated hydraulic conductivity, θs-saturated volumetric moisture content, θi-initial volumetric moisture content). HIGHLIGHT Moisture migration model was derived to improve the quantification of moisture content at an arbitrary point of the soil at any time for the whole process of infiltration under steady rainfall, which shows good accuracy and high adaptability for the moisture migration simulation of a wide range of soil types, and is applicable for short-duration and long-duration steady rainfall.

Experimental Study on the Effect of Key Factors on the Soil–Water Characteristic Curves of Fine-Grained Tailings

The soil–water characteristic curve (SWCC) is an essential parameter for studying the mechanical properties of unsaturated tailings, and it plays an important role in stability assessment and prediction of unsaturated tailings dams. In this paper, the matrix suction was measured indirectly by a filter paper-based method to investigate the effects of key factors (gradation, temperature, and initial dry density) on the soil–water characteristic curves of fine-grained tailings, and the Van Genuchten model was adopted to obtain the empirical equation of SWCC and to verify the accuracy of experimental results. The results showed the following: 1) the Van Genuchten model fits well the relationship between matric suction and volumetric moisture content of fine-grained tailings, indicating that experimental data determined by filter paper-based method is accurate and appropriate; 2) at the same volumetric moisture content, the matrix suction increased with decreasing average particle size, and the decrease in temperature will increase the matrix suction and water-holding capacity of fine-grained tailings, and the matrix suction of the tailings in summer is 38.3% lower than that in winter under the natural volumetric moisture content (14.0%); 3) when the saturation degree of fine-grained tailings is less than 60%, the greater the initial dry density, the better the water-holding capacity and matrix suction.

Moisture Migration and Control of New Embankment for Reconstruction and Expansion Project in Southern China

In hot and humid regions of southern China, the volumetric moisture content of the embankment after opening to traffic for a period of time reaches a stable state, and it is higher than the design value. When it was widened, the humidity gradient and exchange were formed due to the difference in moisture content between the existing and new embankment. To reveal the moisture migration of the existing and new embankment and control the rise of volumetric moisture content in new embankment, six frequency domain reflectometry sensors were installed in existing and new embankment to monitor the volumetric moisture content. A finite element model for the embankment was established and verified with the measured data. And seven numerical analyses of transient seepage in the new embankment of the cushion, cover, and partition using capillary barrier by sand were simulated. The results show that the volumetric moisture contents of the new embankment in southern China gradually increase and eventually reach an equilibrium state. The increase in water comes from the slope, the foundation, and the existing embankment. Early in the first 1∼2 years, the water mainly comes from the foundation and the existing embankment. After that, as time goes by, the water comes mostly from the slope infiltration and gradually migrates to the foundation and the existing embankment. Finally, the volumetric moisture content and the water storage gradually reach equilibrium. The volumetric moisture content of the new embankment using capillary barrier by sand at the cushion, the cover, and the partition is maintained as the construction volumetric moisture content. This combination is a very effective method to control the humidity stability of the new embankment in southern China.

Trends in the variability of potato tuber yield under selected land and soil characteristics

The objective of this study was to evaluate variations in potato tuber yield with the selected land and soil characteristics including (i) topography (elevation and slope); (ii) geometry (horizontal coplanar geometry (HCP)and perpendicular coplanar geometry (PRP)); (iii) hydrology (volumetric moisture content; θv), and (iv) chemistry (phosphate, potash, organic carbon; organic carbon and pH). Analyses of the data collected across four potato fields, two each in Prince Edward Island and New Brunswick (NB), showed that the tuber yield negatively correlated with the field slope and positively correlated with most of the soil characteristics studied. Field elevation affected yield only under certain conditions such as higher range of elevation (≥ 7 m) (Field 2 in NB). Among soil characteristics, only HCP and PRP correlated with field elevation. The slope and elevation explained 22% to 36% variability of yield. Investigations of yield and topography by zonal analysis showed that yield was lower in zones of higher slope or elevation and lower θv, as the mean θv decreased in zones with a higher slope.

Experimental Study on the Effect of Water on the Properties of Cast In Situ Foamed Concrete

This study aims to investigate the effect of water on the properties of cast in situ foamed concrete with a dry density of 300–800 kg/m3 (100 kg/m3 is a gradient). Firstly, the shrinkage deformation with the curing time and the volumetric moisture content is studied by the drying shrinkage test and improved drying shrinkage test. Secondly, the influence of volumetric moisture content on mechanical properties is assessed. At last, the effects of immersion time and immersion type on the mechanical properties of foamed concrete are studied by considering the water-level conditions. The achieved results show that the shrinkage deformations increase with the curing time for the drying shrinkage test and the improved drying shrinkage test, while the variations are different. The shrinkage deformation increases with the decrease of volumetric moisture content for six dry densities of foamed concrete. Besides, it gradually changes in the early stage, while it changes fast in the later stage. The compressive strength and elastic modulus decrease with the increase of volumetric moisture content for each density. For the water-level unchanged condition, the compressive strength and elastic modulus initially decrease and then slowly increase with the increase of the immersion time. For the water-level changed condition, the compressive strength and elastic modulus of foamed concrete decrease with the increase of immersion time for each dry density, and the rate of early attenuation is high, whereas the rate of later attenuation is limited.

Field storage conditions for cattle manure to limit nitrogen losses and optimise fertiliser value

Storage and application of cattle farmyard manure (CFM) can cause considerable environmental problems through nutrient losses to soil, water and air, if not properly handled. We investigated different storage conditions of CFM at field scale to reduce nitrogen (N) losses to the soil, meanwhile optimising the agronomical quality of the CFM. The treatments differed in terms of storage method (stockpiling, extensive composting or co-composting with bulking agents) and coverage (no cover, plastic or geotextile cover). Over the different treatments, the ammonium-N concentrations under the piles in the 0–90 cm soil layer amounted to a maximum of 4.2% of the initial manure N content. We were able to assess the relative importance of each of the two processes resulting in a higher mineral N concentration under the piles, i.e. direct leaching from the CFM to the soil on the one hand, and a smaller indirect effect of elevated soil temperatures (up to 37°C) under the piles resulting in higher N mineralisation in the top soil on the other hand. NH4+-N was the most important component of mineral N under all heaps due to limited oxygen diffusion to the soil. N leaching and end-product quality were affected by a combination of treatment option (i.e. storage and cover) and initial manure characteristics. When CFM was characterised by a low volumetric moisture content and high C : N ratio, so in case of straw-rich CFM or CFM with added bulking agents, composting led to the least N leaching and most stable end product. When CFM was characterised by a high volumetric moisture content and low C : N ratio, stockpiling and covering (plastic or geotextile) resulted in lower N leaching to the soil. Stockpiling and covering the CFM with a geotextile resulted in a more stable end product than did covering with a plastic.

Use of Time Domain Reflectometry to Estimate Moisture and Density of Unbound Road Materials: Laboratory Calibration and Field Investigation

Soil moisture content and dry density of unbound granular pavement materials are important properties for compaction control that influence pavement performance under cyclic loading. Under these loading conditions, increasing moisture content can accelerate significant changes in density. Time domain reflectometry (TDR) is a method for measuring the moisture content and density of soils with rod probe sensors. This paper introduces new calibration functions for TDR measurements using these rod probe sensors embedded in the soil. TDR measurements were taken in the laboratory for a typical road base material at two basically different conditions: at constant moisture content with different dry densities and at constant dry density with different moisture contents. In this study, a relationship was developed between the voltage drop occurring for the passage of an electromagnetic wave through the soil and the bulk density. The permittivity of the soil sample obtained from the travel time of TDR signals was used to calculate the volumetric moisture content. Finally, the gravimetric moisture content was obtained from the volumetric moisture content and bulk density relationship. For the validation of the calibration functions, rod probe sensors were installed in a road to obtain in situ moisture content and density under field conditions. Laboratory results indicate that the calibration functions are independent of moisture and density, and the field test shows the applicability of the method. The newly developed calibration functions allow for the monitoring of the long-term pavement performance, leading to a better understanding of the time-dependent evolution of, for example, rutting of roads.