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The dynamic effects in soil water retention curves (SWRCs) have been the focus of much research. However, most studies implemented short column tests in a few centimeters, under which a semi-permeable porous media inevitably minimizes or magnifies the dynamic effects. In this study, full-scale sand column tests were conducted to eliminate this flaw by preparing a saturated zone under the unsaturated one. The soil suction and moisture profiles were monitored using high-precision tensiometers and spatial time-domain reflectometry, thereby providing a rational overshooting range of the dynamic SWRC. The results confirm that the dynamic primary drainage curve overshoots the static one. The dynamic effects were estimated quantitatively from the soil moisture re-equilibrium time (τS) and dynamic coefficient (τp), falling within reasonable ranges from previous studies. The τp increases log-linearly with decreasing moisture content and can be estimated well from the corresponding τS and the first derivative of SWRC. Also, the τp increases as the soil becomes finer and better graded, which agrees with more-prominent dynamic effects for lower-permeability reservoirs from petroleum studies but disagrees with more-significant dynamic effects for higher-permeability sand from soil-hydrology studies. The analysis shows that the dynamic effects are not dominated solely by the τp or permeability but also by the groundwater dynamics, which can be seen as a pressure boundary from the saturated zone. This finding explains the significant dynamic effects for both high- and ultra-low-permeability geomaterial. Therefore, the present full-scale soil column setup with a prepared saturated zone is recommended for academic investigations of dynamic SWRCs. [ABSTRACT FROM AUTHOR]

The ventilated well method (VWM) is a recently introduced novel dewatering and densification technique for soft soils that relies on controlled evaporation through ventilated and perforated wells traversing through the soil deposit. Several parameters, including geometry of the ventilated well, geometry of the testing mold, soil properties, and properties of the input air, govern the efficacy of the VWM. In this paper, a dimensional analysis (DA)–based approach, following Buckingham's pi theorem, is used to derive the dimensionless π groups for the VWM problem. Using the experimental results from the laboratory-scale implementation of the VWM and multiple regression analysis, a simple dimensionless model between the π groups is suggested. The analysis revealed that, keeping the rest of the parameters constant, the dewatering rate increases with an increase in well diameter, air flow rate, and hydraulic conductivity of soil. However, it decreases with an increase in well height, mold diameter and osmotic suction of the pore fluid. A sensitivity analysis was also performed to understand the relative dependence of the dimensionless dewatering factor on the variation of the four other dimensionless input parameters capturing the influence of the well geometry, mold geometry, soil property, and flow property. Finally, the results from the DA-based model were compared with that obtained from a numerical model, and a good degree of agreement was observed. It is envisaged that both the DA-based model and the numerical model will be useful for scaling the VWM for future experimental work, pilot studies, and field trials. [ABSTRACT FROM AUTHOR]

Although many unsaturated soil experiments have successfully delivered positive outcomes, most studies just concisely illustrated sensor techniques, because their main objectives focused on bridging research gaps. Inexperienced research fellows might rarely follow up those techniques, so they could encounter very trivial and skill-demanding difficulties, undermining the quality of experimental outcomes. With a motivation to avoid those, this work introduces technical challenges in applying three sensor techniques: high precision tensiometer, spatial time-domain reflectometry (spatial TDR) and digital bench scales, which were utilized to measure three fundamental variables: soil suction, moisture content and accumulative outflow. The technical challenges are comprehensively elaborated from five aspects: the functional mechanism, assembling/manufacturing approaches, installation procedure, simultaneous data-logging configurations and post data/signal processing. The conclusions drawn in this work provide sufficient technical details of three sensors in terms of the aforementioned five aspects. This work aims to facilitate any new research fellows who carry out laboratory-scale soil column tests using the three sensors mentioned above. It is also expected that this work will salvage any experimenters having troubleshooting issues with those sensors and help researchers bypass those issues to focus more on their primary research interests. [ABSTRACT FROM AUTHOR]

The strength of unsaturated soil is defined by the soil water retention behavior and soil suction acting inside the soil matrix. In order to obtain the suction and moisture profile in the vadose zone, specific measuring techniques are needed. Time domain reflectometry (TDR) conventionally measures moisture at individual points only. Therefore, spatial time domain reflectometry (spatial TDR) was developed for characterizing the moisture content profile along the unsaturated soil strata. This paper introduces an experimental set-up used for measuring dynamic moisture profiles with high spatial and temporal resolution. The moisture measurement method is based on inverse modeling the telegraph equation with a capacitance model of soil/sensor environment using an optimization technique. With the addition of point-wise soil suction measurement using tensiometers, the soil water retention curve (SWRC) can be derived in the transient flow condition instead of the static or steady-state condition usually applied for conventional testing methodologies. The experiment was successfully set up and conducted with thorough validations to demonstrate the functionalities in terms of detecting dynamic moisture profiles, dynamic soil suction, and outflow seepage flux under transient flow condition. Furthermore, some TDR measurements are presented with a discussion referring to the inverse analysis of TDR traces for extracting the dielectric properties of soil. The detected static SWRC is finally compared to the static SWRC measured by the conventional method. The preliminary outcomes underpin the success of applying the spatial TDR technique and also demonstrate several advantages of this platform for investigating the unsaturated soil seepage issue under transient flow conditions. [ABSTRACT FROM AUTHOR]

High-frequency electromagnetic determination of moisture in porous media, (e.g., soil) is based on the strong relationship between volumetric water content and relative dielectric permittivity. In particular, in fine-grained soils the movement of water is influenced by different surface-bonding forces due to interface processes. The interface effects lead to a number of dielectric relaxation processes (free- and bound-water phase, Maxwell–Wagner effect, counterion relaxation effects). These relaxation processes are the reason for the strong frequency dependence of the electromagnetic material properties below 1 GHz. The matric potential is a measure of the bonding forces on water in the soil. Based on a thermodynamic relationship between soil matric potential and dielectric relaxation behaviour of water in different binding states, a broadband dielectric relaxation model was developed that considers low-frequency dispersion up to 1 MHz as well as losses due to direct-current conductivity. The sensitivity of the model on soil suction was systematically analyzed based on a pedotransfer function (PTF) for soil textures ranging from pure sand up to pure clay. The results are compared with known empirical and semiempirical calibration functions, as well as theoretical mixing models. [ABSTRACT FROM AUTHOR]

• Evaporative surface of deformable soils decreases during evaporation. • Conventional prediction models for soil evaporation do not account for soil deformation during the process. • We propose an improvised method which integrates deformation behaviour of soil while calculating evaporative flux. • The proposed method is based on several controlled laboratory scale tests and analysis. Several methods quantify soil evaporation by measuring vertical moisture flux or by recording change in mass of a soil specimen. These methods conventionally consider a non-deformable soil behaviour. However, shrinkage is the mechanical consequence of a plastic soil to evaporation reducing the area over which evaporation can occur. For this reason, it is imperative to take into account the gradual densification of the soil sample during evaporation in order to minimize possible measurement errors originating from the way, how the physical conditions are simulated. To address this challenge, an improved method proposed in this paper takes into account two aspects of soil deformation, which together have an influence on the total evaporation: (1) the reduced top soil surface due to radial shrinkage and (2) additional evaporation from the exposed side soil surface when the sample detaches from the sample holder. Four experiments with kaolin have been conducted in the laboratory to explore the effect of these two aspects through the proposed methodology. In the tests conducted, considering the changes in the area of the top soil surface and avoiding the additional evaporation from the exposed side surface significantly improved the accuracy of evaporation quantification by 25%. [ABSTRACT FROM AUTHOR]

• Studying scale effects in soil water retention curves (SWRC) by full-scale soil column tests. • Applying spatial time domain reflectometry to determine soil water retention curves. • Observing scale effects in SWRC by comparisons between the proposed and standard tests. • Discussion and illustration of physical reasons for scale effects in SWRC. • Providing SWRC testing recommendations based on the current and prior testing studies. The soil water retention curve (SWRC) is usually measured by the axis translation technique (ATT), assuming a specimen thickness of a few centimetres. Usually, this assumption is unquestionable to ensure the representative elementary volume (REV). However, such an assumption cannot always be conserved with coarser soil regarding the local heterogeneities generated by larger pore sizes. In addition, the authentic SWRC is supposed to be the soil moisture profile above the phreatic surface. Those issues, therefore, raise concerns about the scale effects in SWRC. With an aim to investigate them, this work compared the primary drainage SWRCs of coarse, medium and fine sand measured by the standard hanging column and full-scale soil column (150 cm). The soil moisture profile at the final drainage stage was detected using the spatial time domain reflectometry (spatial TDR) technique with a presentation of sensor calibrations and validations. The observations showed discrepancies between SWRCs given by two methods in terms of air entry value (AEV) and slope of SWRC but agreements on residual moisture content. Moreover, such differences could be alleviated with the soil becoming finer and better graded. Finally, the physical reasons are discussed, referring to local heterogeneity and pressure gradient changes on the top boundary. In conclusion, the full-scale soil column test can be utilised to avoid scale effects, despite demanding high costs and massive labour efforts. Also, a shorter soil column incorporating point-wise suction and moisture sensors in prior studies could be an alternative solution. [ABSTRACT FROM AUTHOR]