Water Retention Behaviour Research Articles

Water retention behavior and microstructural evolution of GMZ bentonite granules upon wetting and drying for deep geological disposal

Water retention behavior and microstructural evolution of GMZ bentonite granules upon wetting and drying for deep geological disposal

Conceptual and Applied Aspects of Water Retention Tests on Tailings Using Columns

The water retention capacity of porous materials is crucial in various geotechnical and environmental engineering applications such as slope stability analysis, landfill management, and mining operations. Filtered tailings stacks are considered an alternative to traditional tailings dams. Nevertheless, the mechanical behaviour and stability of the material under different water content conditions are of concern because these stacks can reach considerable heights. The water behaviour in these structures is poorly understood, particularly the effects of the water content on the stability and potential for liquefaction of the stacks. This study aims to investigate the water retention and flow characteristics of compacted iron ore tailings in high columns to better understand their hydromechanical behaviour. The research used 5 m high columns filled with iron ore tailings from the Quadrilátero Ferrífero region in Minas Gerais, Brazil. The columns were prepared in layers, compacted, and instrumented with moisture content sensors and suction sensors to monitor the water movement during various stages of saturation, drainage, infiltration, and evaporation. The sensors provided consistent data and revealed that the tailings exhibited high drainage capacity. The moisture content and suction profiles were effectively established over time and revealed the dynamic water retention behaviour. The comparison of the data with the theoretical soil water retention curve (SWRC) demonstrated a good correlation which indicates that there was no hysteresis in the material response. The study concludes that the column setup effectively captures the water retention and flow characteristics of compacted tailings and provides valuable insights for the hydromechanical analysis of filtered tailings stacks. These findings can significantly help improve numerical models, calibrate material parameters, and contribute to the safer and more efficient management of tailings storage facilities.

Numerical simulation of rainfall-induced deformations of embankments considering the coupled hydro-mechanical behavior of unsaturated soils

This paper presents numerical simulations of the deformation response of unsaturated embankments subjected to rainfall infiltration using a coupled hydro-mechanical constitutive model for unsaturated soils. The constitutive model accounts for the influence of degree of saturation on the stress–strain behavior and the influence of void ratio on the water retention behavior. The constitutive model was implemented in the finite difference program FLAC, calibrated using triaxial test data, and validated using measurements of wetting-induced deformations of embankment models from centrifuge tests. The validation demonstrates that the constitutive model can capture the coupled hydro-mechanical behavior of unsaturated soils under wetting conditions. Simulations of the hydro-mechanical response of unsaturated embankments subjected to rainfall infiltration indicate that the differential settlement across the top surface of the embankment between the centerline and shoulder increases significantly during rainfall infiltration, which could result in severe damage to overlying transportation infrastructure. As the rainfall infiltration increases, shear strains accumulate and form a potential failure surface at a shallow depth of approximately 2 m from the slope surface. Insights into the hydro-mechanical response of unsaturated embankments subjected to rainfall infiltration gained will be useful for considering climate change effects in design and construction of compacted embankments.

Shrinkage evolution and mechanism of self-curing concrete cooperatively cured with superabsorbent polymers and waterborne epoxy coatings

Shrinkage-induced cracking is a common phenomenon in concrete structures. To reduce concrete shrinkage, herein, a novel curing approach involving the concurrent application of internal superabsorbent polymers (SAPs) and external waterborne epoxy coatings (WECs) was adopted. Subsequently, the combined effects of the SAPs and WECs on the internal temperature, water retention behavior, relative humidity, and shrinkage performance of concrete were investigated. Furthermore, their underlying shrinkage-mitigation mechanisms were clarified and verified through mercury intrusion porosimetry tests. Results revealed that increasing the WEC application rates and number of spraying turns increased the relative humidities and reduced the shrinkage strains of the concrete specimens. The combined use of SAPs and WECs led to considerable reductions in the specimens’ humidity drop, water loss, and shrinkage values. The water losses of the concrete specimens exerted more considerable impacts on their relative humidity and shrinkage compared to their cumulative temperatures. Furthermore, the combination effects of the SAPs and WECs reduced the median pore diameters and increased the fractal dimensions of gel pores, thus triggered a reduce in capillary tension, and further mitigated the development of shrinkage strains. Overall, this study underscores the critical roles of evaporation, temperature, relative humidity, and pore-structure parameters on the shrinkage behavior of concrete. Additionally, it highlights the effectiveness of the combined application of SAP-based internal curing and WEC-based external curing, offering a feasible approach and technical support for reducing shrinkage in concrete structures.

Effective approach to predict soil-water retention curve of bentonites considering adsorption and capillarity

Understanding soil–water retention behavior is a longstanding topic. Water retained in soils can be decomposed into adsorptive and capillary components, controlled by different physicochemical mechanisms. The capillary water retention was frequently discussed in literatures, but the adsorption role was rarely considered, especially for high active clays (e.g., bentonite). In this study, two novel equations for quantifying adsorptive and capillary water retentions are proposed, generating a twofold model to continuously simulate soil–water retention behavior of bentonites. Only 5 parameters, i.e., the maximum adsorption capacity, characteristic adsorptive and capillary suctions, and uniformities of adsorptive and capillary pores, are defined with clear physical meanings. A graphical method was suggested to firstly determine the maximum adsorption capacity, and the remaining parameters are efficiently estimated by non-linear curve fitting. The water retention data for various bentonites, representing a variety of hydration conditions, initial compactness, montmorillonite content and suction range, are used to assess the model performance. The predictions agree well with the measured total, adsorptive and capillary water contents of a Wyoming bentonite, and the fitting curves also match well with test data for other bentonites over the full suction range. Adsorption parameters are distributed within a narrow range, while the characteristic capillary suction is also distributed within a limited range under constant volume condition. The proposed model allows reasonable predictions about the capillary onset and the transition from adsorption to capillarity, revealing obvious superiority by comparison with other hybrid models. This work offers a new pathway to quantitively assess the soil–water retention curve of high active clays.

How does soil water retention change over time? A three‐year field study under several production systems

AbstractAgricultural practices and meteorological conditions affect soil structure and soil hydraulic properties. However, their temporal evolution is rarely studied, and even less in the field. Thus, their dynamics are rarely taken into account in models, often leading to inconsistent results and poor decision making. In this study, the temporal evolution of water retention properties and soil structure was monitored over a 3‐year period under several contrasting production systems. Soil Water Retention Curves (SWRCs) obtained directly in the field (with soil water content and potential sensors) were compared with theoretical SWRCs predicted by pedotransfer functions (PTFs) and laboratory SWRCs measured on undisturbed samples. Bulk densities were measured every 2 months. Results indicate a high degree of variability in SWRCs over time and between production systems. The results suggest that variations in the soil water retention behaviour can be induced by crop differentiation, weed control, crop residue management, compaction during harvest, or the introduction of temporary grassland. Contrasting climatic conditions between 2021 (water excess), 2022 (severe drought) and 2023 (intermediate) provided a unique opportunity to study the resilience of the crop systems to extreme climatic conditions. Different soil drying dynamics were observed and some agricultural practices were identified as influencing the soil water retention behaviour for at least 2 years. Comparison of SWRCs showed that the theoretical curves obtained from PTFs are not a good representation of the field SWRCs, especially for less conventional agricultural practices. The laboratory curves are closer with similar trends. However, these SWRCs are not optimal for investigating the temporal evolution of water retention properties. This research also shows that agricultural practices and crops can be levers for contributing to greater food resilience against future climatic conditions. Therefore, to assess the relevance of production systems for tomorrow's needs, studies should focus on the impact of multi‐cropping systems on water retention dynamics in the field.

A novel framework for deriving water retention behavior of multimodal unsaturated soils based on pore size distribution data

AbstractThe soil water retention curve (SWRC) strongly influences the hydro-mechanical properties of unsaturated soils. It plays a decisive role in geotechnical and geo-environmental applications in the vadose zone. This paper advances a novel framework to derive the water retention behavior of multimodal deformable soils based on the pore size distribution (PSD) measurements. The multiple effects of suction on the soil pore structure and total volume during SWRC tests are considered. The complete picture of soil microstructure is quantitatively described by the void ratio (for the pore volume) and a newly defined microstructural state parameter (for pore size distribution) from a probabilistic multimodal PSD model. Assuming a reversible microstructure evolution, a unique PSD surface for wetting and drying links the SWRC and PSD curves in the pore radius-suction-probability space. A closed-form water retention expression is obtained, facilitating the model's implementation in particle applications. The model is validated using the water retention data of four different soil types, showing a strong consistency between the measurement and the reproduced curve. The proposed method provides new insights into the pore structure evolution, the water retention behavior and the relationship between them for multimodal deformable soils.

Effects of vegetation growth on soil microstructure and hydro-mechanical behaviour

Literature studies are presenting counterposed effects of vegetation on soil hydraulic behaviour. Besides, root impacts at the micro-scale are rarely correlated to phenomenological observations due to the complexity of adopting up-scaling factors. In this study, the microstructural causes behind observed changes in vegetated compacted clayey sand’s hydraulic and volume change behaviour were explored. Laboratory experiments were carried out on compacted samples seeded with Cynodon dactylon. Significant changes in soil water-saturated permeability, water retention and shrinkage upon drying were observed after root growth. Laboratory measurements were complemented by the quantification of root morphological features and observations at the micro-scale for different soil hydraulic states. X-ray scans and mercury intrusion porosimetry allowed to cover seven orders of magnitude of pore sizes, shedding light on soil fabric changes at the soil–root interface and the clay aggregate scale. The effects of roots on the soil pore size distribution consisted of Multiphysics phenomena: fissure generation, void clogging and soil aggregation due to roots’ chemical interaction. Furthermore, a good correlation was found between the normalised volume of roots and the micro-pores volume. This new expression was included in a framework to predict soil water retention behaviour considering the aggregated structure and soil–root hydro-chemical interactions.

Wide-suction-range hysteretic water retention behaviour of compacted soils amended by decomposing hydrochar

Wide-suction-range hysteretic water retention behaviour of compacted soils amended by decomposing hydrochar

Water retention behavior and shear strength of artificially cemented granite residual soil subjected to free drying

Artificially cemented soils have been widely used as filling materials in highway and railway construction. The shear strength evolution of filling materials upon moist variation can determine the stability of subgrade and embankments. This study conducted water retention tests, MIP tests, and multi-stage triaxial shear tests on cement-treated granite residual soil (GRS) to determine its water retention curve (WRC) upon free drying, pore structure, and peak shear strength qf, respectively. The water retention behavior and shear strength evolution upon free drying were modeled based on the dual-porosity structure of cement-treated GRS and the effective stress principle, respectively. Results show that the drying-WRC is bimodal and higher cement dosage yields a more severe decrease in the water retention capacity within a specific suction range. For a given confining pressure, the peak shear strength qf increased with increasing cement dosage or suction value s. The peak shear strength qf also solely depends on the suction value in the peak stress state. In addition, the cement-treated GRS has a bimodal pore size distribution curve, and its macro- and micro-void ratios remain almost unchanged after free drying. The bimodal drying-WRC of the cement-treated GRS can be modeled by differentiating the water retention mechanisms in macro- and micro-pores. Moreover, using the macro-pore degree of saturation as the effective stress parameter χ = SrM, the qf–pf′ relationship (where pf′ is the effective mean pressure at failure) under various suction and stress conditions can be unified, and the qf–s relationships at various net confining pressures σ3,net can be well reproduced. These findings can help design subgrade and embankments constructed by artificially cemented GRS and assess their safe operation upon climate change.

Effect of volumetric deformation on saturation of unsaturated soils under constant suction

The soil–water retention curve (SWRC) represents a fundamental relationship in the study of unsaturated soils, where volumetric deformation plays a crucial role in shaping the water retention characteristics by impacting the pore size distribution. This study conducted a thermodynamic analysis to derive a relationship between the effective stress parameter and the water retention properties of unsaturated soils. Consequently, a streamlined formula was introduced to forecast the impact of volumetric deformation on saturation at constant suction. This formula, incorporating a singular parameter from the effective stress parameters equations, can be seamlessly integrated with any prevailing SWRC model to characterize the influence of volume deformation on the SWRC. The effectiveness of the proposed model was corroborated through seven sets of experimental data spanning various soils, affirming its capability to precisely describe the water retention behavior of deformable soils under deformation.

Synthesis, swelling and water-retention behaviors of phytic acid-modified corn stalk-composite superabsorbents

Synthesis, swelling and water-retention behaviors of phytic acid-modified corn stalk-composite superabsorbents

Data-driven discovery of interpretable water retention models for deformable porous media

The water retention behavior—a critical factor of unsaturated flow in porous media—can be strongly affected by deformation in the solid matrix. However, it remains challenging to model the water retention behavior with explicit consideration of its dependence on deformation. Here, we propose a data-driven approach that can automatically discover an interpretable model describing the water retention behavior of a deformable porous material, which can be as accurate as non-interpretable models obtained by other data-driven approaches. Specifically, we present a divide-and-conquer approach for discovering a mathematical expression that best fits a neural network trained with the data collected from a series of image-based drainage simulations at the pore-scale. We validate the predictive capability of the symbolically regressed counterpart of the trained neural network against unseen pore-scale simulations. Further, through incorporating the discovered symbolic function into a continuum-scale simulation, we showcase the inherent portability of the proposed approach: The discovered water retention model can provide results comparable to those from a hierarchical multi-scale model, while bypassing the need for sub-scale simulations at individual material points.

Analysis of Soil–Water Characteristic Curve and Microstructure of Undisturbed Loess

Long-term irrigation promotes the infiltration of water in the thick, stratified loess layer, significantly raising the groundwater table and triggering a series of landslides in loess platform areas. The soil–water characteristic curve (SWCC) of loess buried at different depths affects the unsaturated infiltration process and is intricately connected to the soil’s microstructure. The SWCCs, scanning electron microscope (SEMs), and pore size distributions (PSDs) for five sets of undisturbed loess samples at depths ranging from 3.4 to 51.9 m are shown in this paper. The results indicate that the fitting parameter air entry value (AEV) of the SWCC rises from 13.67 kPa to 40.19 kPa as the depth increases from 3.4 to 51.9 m. And the saturated volumetric water content drops by 10.9%, with a notable SWCC shape difference between the transition and residual zones observed. Additionally, the total porosity of undisturbed loess falls by 12% when the depth increases from 3.4 to 51.9 m, while the macropores and mesopores reduce by 3.6% and 12.1%, respectively. These findings highlight the control of the pore structure on the SWCC and emphasize the correspondence between the SWCC and PSD. The conclusions also illustrate that the compaction effect changes the microstructure characteristics of loess, thereby affecting the soil’s water retention behavior.

Hysteretic water-retention behaviour of unsaturated hydrophobised soils

Hydrophobised soils found in the superficial region of earthen infrastructure can affect the hydrological processes of these structures. The hysteretic water-retention curve (WRC), which governs these processes, for hydrophobised soils has rarely been reported. Existing apparatus is unable to measure the WRC of unsaturated soils as it could not control the condition of pore water pressure (uw) in excess of pore air pressure (ua) when the contact angle was larger than 90°. In this study, a new apparatus was created, which sandwiches a soil sample between a high water-entry value (WEV) membrane and a high air-entry value (AEV) ceramic disc, to control the uw < ua and uw > ua conditions. Contact angle hysteresis and menisci evolution in the test materials during wet–dry cycles were measured to interpret the WRC. The WEV of soil increased with decreasing chemical heterogeneity and particle size. When drying the hydrophobised soils, they could retain water before reaching a certain negative uw. The WEV identified from the second wetting cycle was lower than that from the first cycle, whereas the AEV remained largely unchanged. The WEV and AEV decreased when the particle size of the hydrophobised materials was increased, resulting in a smaller hysteresis size.

Novel nano-fertilizers derived from drinking water industry waste for sustained release of macronutrients: performance, kinetics and sorption mechanisms

Nanotechnology has emerged as a promising approach for the controlled release of nutrients, particularly phosphorus and potassium. These essential plant nutrients are often applied in excess, leading to environmental pollution and loss of efficiency in crop production. Innovative economic and highly efficient fertilizers are urgently needed to achieve the targeted crop production worldwide in the presence of limited land and water resources. Therefore, in this study, novel, eco-friendly, cost-effective and enhanced efficiency nano-enabled fertilizers, NEF (nWTF1and nWTF2) were synthesized by impregnation of nanostructured water treatment residuals (nWTR) with (KH2PO4 + MgO) at 1:1 and 3:1 (w/w) ratios respectively using a planetary ball mill. The nWTR, nWTF1 and nWTF2 were extensively characterized. The water retention behavior and the sustained release of nutrients from the fabricated nano-enabled fertilizers (nWTF1 and nWTF2) in distilled water and sandy soil were investigated and monitored over time. The water retention capacity of the soil treated with nWTF2 after 26 days was 9.3 times higher than that of soil treated with conventional fertilizer. In addition, the nWTF2 exhibited lower release rates of P, K and Mg nutrients for longer release periods in comparison with the conventional fertilizers. This is a significant advantage over traditional fertilizers, which release nutrients quickly and can lead to leaching and nutrient loss. The main interaction mechanisms of PO4–K–Mg ions with nWTR surface were suggested. The results of the kinetics study revealed that power function was the best suitable model to describe the kinetics of P, K and Mg release data from NEF in water and soil. The produced NEF were applied to Zea maize plants and compared to commercial chemical fertilizer control plants. The obtained results revealed that the nano-enabled fertilizers (nWTF1 and nWTF2) significantly promoted growth, and P content compared with the commercial chemical fertilizer treated plants. The present work demonstrated the power of nano enabled fertilizers as efficient and sustained release nano-fertilizers for sustainable agriculture and pollution free environment.

A graph-based approach for modeling the soil–water retention curve of granular soils across the entire suction range

This study investigates experimentally the water retention behavior of granular soils from saturation to oven-dry state. The soil–water retention curve (SWRC) tests were conducted on a well-graded sand with clay using tensiometer and chilled-mirror hygrometer techniques. The soil samples were statically compacted at various water contents to different initial densities. The results showed that individual linear segments in the log–log graph could characterize the desorption process of capillary and adsorption water. A novel water retention model in a simple mathematical form was developed by conceptualizing the total water content as the sum of the suction-dependent capillary and adsorption components. The model parameters possess an unambiguous physical meaning. They can be easily calibrated based on the graphical properties of the test data using simple linear regression, which is a significant advantage over conventional SWRC models. The model was validated using the water retention data of the tested soil in this study and the available data of granular soils in the literature. The reproduced curves agree well with the experimental results. This study also analyzed the influence of compaction water content, initial density, and clay content on the capillary and adsorption components of the water retention curve. Additionally, the proposed framework provides a quick approximation method for the adsorption capacity, which plays an essential role in assessing the effective stress and the simulation of liquid film flow in unsaturated granular soils.

Effects of Compaction Water Content on Water Retention and Deformation Behavior of Compacted Loess

Compacted loess is widely used as a construction material in engineering practices. The compaction dry density and compaction water content have significant effects on the hydromechanical behavior of compacted loess, thereby influencing the serviceability and safety of engineering structures. The former was widely studied in previous studies, while the latter is rarely known. In this study, the water retention, compression, and collapse behavior of compacted loess at different compaction water contents are investigated through pressure plate and oedometer tests. Microstructure analysis was carried out for insight analysis of the test results. The air entry value and yield stress of compacted loess decreased by 64% and 50%, respectively, with the compaction water content increasing from 12.4% to 19.0%. This is due to the fact that the number of clods increases with increasing the compaction water content, leading to many large-sized pores (i.e., diameter > 1,000 μm) and weaker soil skeletons. The influence of compaction water content on the water retention and compression behavior of loess is more pronounced at lower compaction dry densities and lower testing water contents, respectively. In addition, the specimen shows smaller collapse indexes at higher compaction water contents, mainly because of the larger deformation induced by the initial compression.

Effects of Cement Treatment on Water Retention Behavior and Collapse Potential of Gypseous Soils: Experimental Investigation and Prediction Models

Gypseous soil poses a significant challenge in geotechnical engineering due to its susceptibility to collapse under saturation. This type of soil covers approximately 33% of regions in Iraq, primarily in unsaturated conditions. This study focuses on two types of gypseous soils: one with moderate gypsum content from Karbala city (G1) and the other with high-gypsum content from Tikrit city (G2), to investigate the effects of cement treatment on their water retention behavior and potential for reducing collapse. Different percentages of cement were mixed with both soils to determine the optimum soil–cement mixture for reducing collapse potential (CP) through single oedometer tests. The water retention characteristics and water retention behavior of samples with varying gypsum content and different levels of cement treatment were examined and compared using a controlled-suction oedometer. The soil–water retention curve (SWRC) of these natural and treated gypseous soils was also investigated and compared in both wetting and drying paths. Additionally, multiple pedotransfer functions (PTFs) were assessed to identify or adapt prediction equation(s) for the SWRC of gypseous soil both with and without cement treatment with acceptable accuracy. The results show that adding cement can decrease the CP of gypseous soils; it also affects their SWRC significantly. By making some simple modifications, the PTFs demonstrate acceptable estimations for the water retention curve of both natural and cement-treated gypseous soils.

Evolution of water content and suction of Opalinus Clay from recovery at the drilling site to handling in the laboratory

Advanced geotechnical engineering applications, such as shale gas extraction, CO2 geological sequestration, and geological radioactive waste storage, often involve various types of shales located at significant depths. Shales exhibit mechanical properties that are highly influenced by their hydration state and are exposed to substantial stress relief during extraction from considerable depths. This results in the development of elevated total suction (free energy per unit volume of pore water). While water content measurements are conventionally employed for characterizing these materials, ongoing discussions and uncertainties persist regarding the relevance and representativeness of laboratory suction measurements, particularly in light of potential influences stemming from core extraction and conditioning processes. A recent extensive borehole drilling campaign has provided a unique opportunity to offer scientific insights into specimens of Opalinus Clay shale, extracted from various locations and depths. These specimens were examined in their freshly extracted on-site condition and their freshly opened condition in the laboratory. Notably, it has been observed that suction and water content measurements acquired on-site immediately after core extraction differ from those obtained in the laboratory. The evolution of suction and water content from the field to the laboratory is closely linked to the main drying water retention behavior of the geomaterial.