Influence of microstructure on drying- and wetting-characteristics of fine-grained soils (original) (raw)
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Geomechanics and Geoengineering, 2018
The soil water retention characteristics curve (SWRC) has been reported to be quite useful for estimation of unsaturated soil properties. However, the uniqueness of SWRC is questionable due to hysteresis associated with the drying-and wetting-path SWRCs and this poses great challenge in utilising the SWRC for reliable estimation of unsaturated soil properties. Although hysteresis associated with SWRCs has been extensively studied for coarse-grained soils, due to limited studies on wetting-path SWRC for fine-grained soils, the hysteresis for fine-grained soils is not well understood. The present work attempts to address this gap, by studying the drying-and wetting-path SWRCs for eight different finegrained soils by employing Dew point Potentiameter (WP4C ®), Environmental Chamber and Controlled Water Sprinkling method. The study employs the concept of 'Suction Hysteresis', ψ h , for quantification of hysteresis. Further, the influence of various soil-specific properties on the variation of ψ h-water content relationship (viz., slope of variation of suction hysteresis, S ψh) has also been studied and demonstrated. The findings of the study are quite encouraging and it has been realised that extensive studies on soils of different characteristics would be quite useful in quantifying the variation of SWRC during drying and wetting cycles.
Influence of Drying and Wetting Cycles on SWCCs of Fine-Grained Soils
Journal of Testing and Evaluation, 2012
The soil-water characteristics curve (SWCC) is greatly influenced by the path that is followed for suction measurement (i.e., drying or wetting path) and the number of cycles of these paths to which the soil is exposed. To evaluate the influence of these parameters, drying-and wetting-path SWCCs of three fine-grained soils were developed for single and multiple cycles by employing the Aquasorp V R Isotherm generator. This device has been primarily employed for food products, powders, and amorphous materials for determination of their moisture sorption isotherm, which relates moisture content to water activity. As water activity can be mathematically related to soil suction, the Aquasorp V R can be used for developing the SWCC. Hence, demonstrating the potential of the Aquasorp V R for characterizing fine-grained soils becomes essential. The present study has been focused at highlighting the possible uncertainties associated with establishment of the SWCCs (both during drying and wetting paths) and the benefits and limitations of the Aquasorp V R in achieving these objectives. Furthermore, by employing mercury intrusion porosimetry (MIP), the significance of capillarity on soil suction, which in turn governs the SWCC, has been demonstrated.
Water retention in unsaturated soils subjected to wetting and drying cycles
2011
The suction is an essential parameter to describe and understand the behavior of unsaturated soils. The ability of unsaturated soils to retain water is quantified by determining the water retention curves (WRC), which express the hydraulic behavior of porous materials such as soil. These curves are determined by subjecting samples to several drying and wetting cycles. The curve during drying path is located above the wetting curve, developing a hysteresis phenomenon [1], and value of content water at a given suction value depends on the path used to reach this point. The aim of this paper is to present a study on the hydraulic behavior of soil, water retention capacity due to drying and wetting cycles, pointing out the hydro-mechanical behavior of unsaturated soils. In the first part, the effect of physical and mechanical properties of soil [32] (initial void ratio, particle size, cohesion, density...) on the water retention is presented. In the second part, a complete numerical model was developed, based on the empirical model of Van Genuchten [18], to model the two boundary curves, and the experimental scanning data were bestfitted using the same theory of Mualem model [13]. This complete model requires 4 parameters.
Acta Geotechnica, 2017
The main objective of this paper is to examine how different engineering soils react to environmental variations and to provide correlations to characterize their behaviour under null external mechanical stress. Two French and two Algerian soils with liquid limits ranging from 36 to 112 were prepared under both slurry and Proctor compaction conditions, and then subjected to drying-wetting paths with suction controlled from several kPa to several hundreds of MPa. Experimental results are presented in five diagrams to show globally and simultaneously the shrinkage-swelling, saturation-desaturation and water retention characteristics. A reasonable consistency was observed between the oedometric and drying curves of slurry, confirming the equivalence between hydraulic loading (suction) and mechanical loading (consolidation stress) on the volume change behaviour of different soils. As an intrinsic parameter of soil nature, liquid limit was found to have a significant influence on the shrinkage limit, air-entry suction and compressibility of both slurry and compacted samples. For that reason, correlations between these characteristics and liquid limit were set up, providing a good basis for a first estimation of the drying-wetting curves. At the micro-scale, new experimental results were obtained: either on drying or wetting path, the micro-pores were almost unaffected, whereas, when matrix suction increased from 0.1 to 8 MPa, the volume of macro-pores decreased to quasi-closure. At last, the analogy between the compaction and drying-wetting curves, and the comparison of different methods to determine the water retention curve were addressed. Such analogies and comparisons contribute to a better understanding of the mechanisms of mechanical stress and suction.
Quantification of hysteresis effects on a soil subjected to drying and wetting cycles
A b s t r a c t. A quantitative description of soil hysteretic response during drying-wetting cycles is required to improve prediction of the soil water retention model. The objective of the study is to quantify the degree of hysteresis, which is helpful to evaluate the precision of soil water flow calculation. A new procedure to quantify the degree of hysteresis is presented. The Arya-Paris model allows assessment of hysteresis effects from initial drying curves, dynamic contact angles, degree of hysteresis value, and maximum difference value between drying and subsequent wetting curves. The experimental results show that the degree of hysteresis varies with the particle size, bulk density, void ratio, initial water content, and contact angle of the soil. The new findings can be very useful in modelling soil water flows.
Effect of wetting on pore structure of compacted fine-grained soils
2011
Pore structure of fine-grained soils can be affected by wetting and drying cycles. The flow of water in vertical and lateral directions occurs through the pores in these soils. However, redistribution of these pores due to wetting and drying could affect the hydraulic conductivity of fine-grained soils. The purpose of this study is to investigate the change in soil structure before and after the wetting at the microscopic level. Compacted samples prepared from two natural clay-rich deposits which are widely used as landfill liner material were subjected to wetting. Specimens were taken from these samples before and after wetting for Scanning Electron Microscope (SEM) observations. It was found that wetting influenced the pore structure of both fine-grained soils and this may be attributed to the change in hydraulic conductivity of the landfill barrier layers.
Prediction of soil water retention properties using pore-size distribution and porosity
Canadian Geotechnical Journal, 2013
Several models have been suggested to link a soil's pore-size distribution to its retention properties. This paper presents a method that builds on previous techniques by incorporating porosity and particles of different sizes, shapes, and separation distances to predict soil water retention properties. Mechanisms are suggested for the determination of both the main drying and wetting paths, which incorporate an adsorbed water phase and retention hysteresis. Predicted results are then compared with measured retention data to validate the model and to provide a foundation for discussing the validity and limitations of using pore-size distributions to predict retention properties.
Factors affecting drying and wetting soil-water characteristic curves of sandy soils
Canadian Geotechnical Journal, 2004
Drying and wetting soil-water characteristic curves (SWCCs) for five sandy soils are investigated using a Tempe pressure cell and capillary rise open tube. The test data are fitted to two SWCC equations using a least-squares algorithm. The obtained fitting parameters and some hysteretic behaviour are discussed and correlated with grain-size distribution parameters. A concept of total hysteresis is proposed to quantify the hysteresis of SWCC. The measured SWCC for one soil is also compared with the SWCC estimated from its grain-size distribution. The SWCC was also obtained at a high dry density for one of the soils. The results show that the shapes of the SWCCs are similar to the grain-size distributions of the soils and are affected by the dry density of the soil. A coarse-grained soil has a lower air-entry value, residual matric suction, and water-entry value and less total hysteresis than a fine-grained soil. The residual matric suction and water-entry value tend to approach the s...
Evaluation of Soil-Water Characteristic Curve and Pore-Size Distribution of Fine-Grained Soils
Water
A soil’s physical properties, mineral types, and pore structure significantly influence the shape and properties of the soil-water characteristic curve (SWCC). This study investigated the effects of the soil’s physical properties and mineral types on the SWCC and pore-size distribution (PSD). Eight different soils from an alluvial deposit in Istanbul and Adapazarı/Türkiye were used in the study. The test samples were prepared by compaction at optimum water content (OWC) and wet side of optimum water content (wet of OWC). The samples were prepared by consolidation from the slurry. The PSDs of the samples were calculated using the SWCCs and evaluated with scanning electron microscope (SEM) analysis. In addition, the mineral types of all soils were determined by X-ray diffraction analysis. The soil which contains illite-type minerals has higher matric suction than containing kaolin-type. The effect of the clay percentage is more pronounced in silty soils than in plasticity and activity...
Soil porous system changes quantified by analyzing soil water retention curve modifications
Soil & Tillage Research, 2008
Soil water retention curves (SWRC) relate soil water pressure head (h) to soil water content (θ) and can also be used to find information regarding soil pore distribution. To analyze SWRCs in relation to pore size distribution (PSD), changes due to wetting and drying (W-D) cycles were studied in three different tropical soils (Geric Ferralsol, GF; Eutric Nitosol, EN;