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Article

Influence of Desaturation and Shrinkage on Evaporative Flux from Soils

Environmental Systems Engineering, Faculty of Engineering and Applied Science, University of Regina, 3737 Wascana Parkway, Regina, SK S4S 0A2, Canada
*
Author to whom correspondence should be addressed.
Submission received: 20 April 2022 / Revised: 14 May 2022 / Accepted: 20 May 2022 / Published: 22 May 2022

Abstract

:
An assessment of evaporation losses from soils is critical for sustainable agriculture in semi-arid regions. The purpose of this research was to determine the effect of desaturation and shrinkage on evaporative flux from representative soils. Results indicated that the surface area did not change for silty sand (6% volume reduction) and substantially increased for lean clay (17% volume reduction). The evaporative flux for silty sand decreased from 31 to 25 mg/m2∙s in Stage II, remained constant during Stage III, and decreased to 11 mg/m2∙s in Stage IV. In contrast, the lean clay showed a longer Stage II (34 to 14 mg/m2∙s), a near constant Stage III, albeit a similar Stage IV (13 to 3 mg/m2∙s). The air entry and residual suction values were 1 kPa and 100 kPa for silty sand and 5 kPa and 1400 kPa for lean clay. In both soils, the total suction merged with the matric suction at Stage IIStage III boundary. Furthermore, the shrinkage curve was J-shaped for silty sand with the only void ratio decrease in Stage II, whereas that for the lean clay showed a significant void ratio decrease in Stage II, marginal decrease in Stage III, and no decrease in Stage IV. Under high demand, the silty sand exhibited Stage III and Stage IV evaporation, whereas the lean clay also showed significant flux during Stage II. For the investigated range of water content, the total water loss under high demand was found to be 7 times that under low demand.

1. Introduction

Agricultural farmlands in the semi-arid climate zones of the Canadian Prairies are challenged by a scarcity of water [1]. Sustainable farming in this part of the country necessitates an adequate water storage in the soil for plant growth, among other requirements [2]. This is particularly true for southern Saskatchewan, where a new irrigation system is being developed for improved crop productivity. Such a system is expected to lose water to the atmosphere under the prevalent regional climate, which is responsible for an estimated potential evaporation (PE) of about 1800 mm/year from free water surfaces [3]. Actual evaporation (AE) from soil surfaces is quite complex and is affected by surface–atmosphere interactions [4] and the properties and behaviour of soils [5]. Moreover, this process is related to desaturation that increases from the top-down due to decreasing exposure to the atmosphere, since AE mainly occurs through the soil pores [6]. The main challenge in understanding water retention in soils is the accurate determination of relevant parameters [7] and the associated shrinkage in clayey soils that, in turn, exposes additional area of the soil to evaporation [8]. Clearly, there is a need to investigate the effect of desaturation and shrinkage on the evaporative losses in soils.
Several experimental studies have been conducted to determine evaporative fluxes from regional soils, including sand, silt, and clays. Based on short-term (3 h to 5 h) laboratory tests on inert sand and silt from Beaver Creek Conservation, Saskatchewan, Wilson et al. [9] developed a correlation between total suction and AE/PE. These authors found that their equation was not reliable when tested for clays from Regina, Saskatchewan. Huang et al. [10] conducted moderate-term (60 d) column tests using the above sand and silt in homogenous and stratified form and found that textural variations significantly affect actual evaporation. Staple [11] conducted long-term (22 y) non-draining field lysimeter tests on clays from Swift Current, Saskatchewan, to predict actual evaporation that was found to be applicable in the local atmospheric conditions only. Khan and Azam [12] conducted moderate-term (11 d) laboratory tests on clays from Avonlea, Saskatchewan, and determined that gradual radial exposure of the soil affects the mass change rate, although the effect of atmospheric demand was not evaluated. To date, there is no research that investigates the coupled processes of desaturation and shrinkage and their combined effect on evaporative fluxes from soils.
The main objective of this research was to investigate the effect of desaturation and shrinkage on evaporation from soils. First, a literature review is provided to correlate evaporation stages with soil behaviour. Second, a comprehensive research methodology was developed using newly developed test systems. Third, evaporative fluxes from inert and active soils were measured and analyzed in conjunction with water retention and soil shrinkage. Fourth, evaporative fluxes were determined using high atmospheric demand prevalent in the region.

2. Literature Review

Evaporative flux from agricultural soils is a significant problem in the semi-arid Canadian Prairies and requires expensive irrigation infrastructure to maintain a water content adequate for plant growth [13]. The geologic history of the area results in a wide spectrum of soil types, ranging from inert sands and silts to active clays [14]. The main issue with soils of varying composition is the differing rates of evaporative flux, along with volumetric shrinkage that affects irrigation scheduling requirements [15].
Figure 1 presents a conceptual relationship between surface evaporation, water retention, and soil shrinkage with respect to gravimetric water content (w) for soils. Evaporative flux (Figure 1a) is defined as the mass of water passing through an exposed surface area per unit time [16]. When soils have surface areas that remain relatively constant throughout drying [17], the rate of change in evaporative flux at the soil surface is directly related to the rate of change of water mass [18]. Generally, soils exhibit five different evaporation stages [19]: Stage I, highest rate because the soil remains saturated and covered with a water film to ensure continuous potential evaporation [9]; Stage II, decreasing rate because air begins to enter the largest soil pores to initiate capillary flow [20]; Stage III, constant rate because the capillary pore network ensures steady water supply to the surface [21]; Stage IV, decreasing rate because the pore system becomes discontinuous due to the presence of occluded air [22]; and Stage V, decreasing rate because vapour transport is the dominant flow mechanism [19]. These stages exist under low atmospheric demand, that is, PE < 5 mm/day (58 mg/m2∙s) [5]. At higher values of atmospheric demand, Stage III is absent owing to the high exchange of vapour between the atmosphere and the evaporating surface [23].
The water retention curve (WRC in Figure 1b) correlates soil suction with the amount of water held within the soil [24]. This plot is governed by physical properties, such as grain size distribution, dry unit weight, clay content, and soil microstructure [25]. Total suction is the negative pressure developed within soil pores due to drying. It consists of matric suction due to capillarity and adsorption as well as osmotic suction that is driven by the constant effects of salt content [26]. The WRC generally comprises three components: a nearly horizontal line up to the air entry value (AEV), a rapid decrease in water content from AEV to the residual suction value (RSV), and low decrease from RSV to completely dry soil [27]. The boundary effect zone (corresponding to Stage I evaporation) is where the soil pores are nearly saturated, and the change in water is independent of soil suction up to the AEV [28]. The AEV (corresponding to the start of Stage II evaporation) marks the point when air enters the largest pores in the soil. The transition zone (corresponding to Stage III evaporation) pertains to water migration through the capillary network of the soil [29]. The RSV (corresponding to Stage IV evaporation) marks the point where the water phase in the soil becomes discontinuous and the pores begin to disconnect due to occluded air [5]. The residual zone (corresponding to Stage V evaporation) occurs under large suction values required to remove adsorbed water through vapor diffusion [30].
The soil shrinkage curve (SSC) is a relationship between void ratio and the water content and correlates volumetric changes in soils during drying [31]. The shape of the SSC is influenced by soil type and soil microstructure [32]. Inert soils show a J-shaped curve with two slopes: an initial small decrease due to normal shrinkage (corresponding to Stage I evaporation) where the volume of water loss is equal to the volume reduction in soil, that is, close to saturation line [33]; and no decrease until completely dry conditions (covering all of the remaining evaporation stages) because of a lack of shrinkage capability in such soils [34]. In contrast, active soils show an S-shaped curve comprising three slope [29]: a near-horizontal line of structural shrinkage (corresponding to Stage I evaporation), where the largest soil pores are nearly saturated and result in evaporation similar to that from water surfaces [35]; a parallel to saturation line of normal shrinkage (corresponding to Stage II through Stage IV evaporation), where the volume of water loss equals the change in soil volume [36]; and a near-horizontal line of marginal shrinkage (corresponding to Stage V evaporation), where soil undergoes drying due to the partial removal of adsorbed water [37].
This framework demonstrates that soil behavior (WRC and SSC) during evaporation for inert sands is quite different from active clays. Therefore, a comprehensive investigation requires the use of the following: (i) test systems such as controlled photogrammetry for capturing volumetric deformations in soils; (ii) test methods such as filter paper for accurate measurement of soil suction; (iii) appropriate parameters for various deformations during evaporation and their correlation with WRC; and (iv) evaporation tests under simulated regional weather conditions.

3. Materials and Methods

3.1. Soil Selection and Classification

Representative soils were collected from southern Saskatchewan, including an inert silty sand from Avonlea [38] and an active lean clay from Belle Plaine [39]. At each location, the surface soil was manually retrieved using a shovel, sealed in plastic bags to preserve moisture, and put in 20 L buckets to preclude impurities. The samples were transported to and stored in the thermostatically-controlled (nominally at 20 °C) Advanced Geotechnical Testing Laboratory at the University of Regina following the Standard Practices for Preserving and Transporting Soil Samples (ASTM D4220/D4220M-14).
Table 1 presents a summary of the geotechnical index properties, including the grain size distributions (Figure 2). The specific gravity (Gs) of the soils was determined using the Standard Test Methods for Specific Gravity of Soil Solids by Water Pycnometer (ASTM D854-14). The grain size distribution was determined by a combination of the Standard Test Methods for Particle-Size Distribution (Gradation) of Soils Using Sieve Analysis (ASTM D6913/D6913M-17) and the Standard Test Method for Particle-Size Distribution (Gradation) of Fine-Grained Soils Using the Sedimentation (Hydrometer) Analysis (ASTM D7928-21). The poorly-graded silty sand (Gs = 2.66) had only 5% material finer than 0.002 mm, whereas the well-graded lean clay (Gs = 2.69) had 31% material finer than 0.002 mm. The consistency limits were determined using the Standard Test Methods for Liquid Limit, Plastic Limit, and Plasticity Index of Soils (ASTM D4318-17e1). These limits are gravimetric water content values at critical stages in soil behavior. Soil flows like a liquid when the water content is above the liquid limit and starts to crumble when the water content is below the plastic limit. Likewise, the plasticity index (difference between liquid limit and plastic limit) indicates the range of water contents within which the soil exhibits plasticity. The water adsorption and retention capability of the silty sand (wl = 27% and wp = 25%) was found to be lower than that for the lean clay (wl = 32% and wp = 18%). The shrinkage limit (ws) was determined using the method given in Holtz et al. [40], which was found to be non-existent for silty sand and 14% for the lean clay. This limit pertains to the gravimetric content at which the volume of a soil is minimum. The two materials were classified using the Standard Practice for Classification of Soils for Engineering Purposes (Unified Soil Classification System) (ASTM D2487-17) as silty sand (SM) and lean clay (CL), respectively.

3.2. Sample Preparation

Table 2 gives a summary of the initial conditions for the investigated soil samples. Two types of samples were prepared, namely saturated samples (w ≈ 40%; θ ≈ 50%) to capture the entire range of soil behavior under low demand, and unsaturated samples (w ≈ 27%; θ ≈ 35%) to simulate field conditions under high demand. In both cases, samples were prepared based on a dry density of 1.3 g/cm3 that is typical of soils in the region. The degree of saturation (S) was calculated using water content (w), specific gravity (Gs), and void ratio (e) according to the following equation [29]:
S = w · G s / e
Likewise, the volumetric water content (θ) was calculated using water content (w), dry unit weight ( γ d ), and unit weight of water ( γ w ) as per the following equation [29]:
θ = w · γ d / γ w
Figure 3 presents the various stages of sample preparation. The collected soils were broken down using a mortar and pestle and oven dried at 110 °C for 24 h to remove moisture [9]. Approximately 24 g of dry soil was placed in a sample cup with an internal volume of 18.6 cm3 (Figure 3a) and the former was gently tamped to achieve a level surface (Figure 3b). Saturated samples were prepared by adding 9.5 g of distilled water to the dry soil. The mixture was sealed in a close-fitting container to allow the water to homogenize within the soil while precluding evaporative losses [17]. After 12 h, the samples were removed from the container (Figure 3c) and gently tamped down to the rim-height to cancel any swelling in the clay (Figure 3d). Likewise, unsaturated samples were prepared by adding 6.7 g of distilled water to the dry soil and following the remainder of the steps as before.

3.3. Evaporation Testing and Volumetric Capture

Low demand evaporation tests were conducted using saturated samples under the ambient laboratory atmosphere. The sample was alternatively placed in an enclosure over a high-precision scale (A&D Apollo GX-603A) to measure its mass (at 4 h intervals for up to 16 h and thereafter at 8 h intervals for up to 72 h) and in the Controlled Photogrammetry System (CPS) to determine its dimensions (that generally took 25 min to complete) following the procedure given by Suchan and Azam [17]. Four distinct types of soil deformation were obtained: (i) horizontal deformation ( D d , %), ratio of sample diameter at time t ( d t ; mm) to the initial diameter ( d 0 ; mm); (ii) vertical deformation ( D h , %), ratio of sample height at time t ( h t ) to the initial height ( h 0 ); (iii) surface area deformation ( D s , %), ratio of exposed area (including the top and the sides) at time t ( s t ) to the initial exposed area at 0 hours ( s 0 ); and (iv) volume deformation ( D v , %), ratio of total sample volume at time t ( v t ) to the initial volume at 0 hours ( v 0 ).
High demand evaporation tests were conducted using unsaturated samples in the Bench-scale Atmospheric Simulator (BAS2), in which summer day conditions of the Canadian Prairies [3] were simulated following the procedure given by Suchan and Azam [41]. The soil sample was placed on the mass scale in the climate chamber and the test was conducted over 6 h, with the various parameters affecting evaporation thoroughly monitored using high-precision sensors.
Table 3 presents a summary of the measured atmospheric and surface parameters. The low demand tests collected more than 8600 data points at 30 s intervals. The air velocity at surface was found to be less than 0.1 m/s because the mass balance had glass side-protectors and a partially-covered roof that precluded cross-winds. Likewise, the air pressure and relative humidity were measured next to the mass balance and recorded values of about 96 kPa and 27%, respectively. The thermostatically-controlled air temperature registered 21.4 °C. The test samples were mostly kept under dark conditions, except during the 25 min CPS sessions, thereby ensuring negligible values for both incoming and outgoing shortwave energy fluxes.
The high demand evaporation tests collected about 2160 data points at 10 s intervals. The air velocity was kept at 1.3 m/s. The summer day air pressure was recorded to be 93.5 kPa. Likewise, relative humidity and air temperature measured 55.5% and 18.9 °C, respectively. An externally-mounted light source in a nadir-position above the sample delivered 325 W/m2 of incoming shortwave energy of the solar spectrum such that 1 W/m2 was reflected back. The surface temperature was recorded to be 22.1 °C. These data indicate good precision and repeatability under controlled conditions because spatio-temporal variations in atmospheric parameters and physiographic features were precluded.

3.4. Water Retention

The drying WRC was determined according to the Standard Test Method for Measurement of Soil Potential (Suction) Using Filter Paper (ASTM D5298-16) through the Whatman No. 42 filter paper for simultaneous measurement of total and matric suction [42]. The bi-linear calibration curve (given by Greacen et al. [43] and recommended by ASTM) was used to ensure accuracy [44]. Likewise, water content was measured as before. Twenty (20) identical samples were prepared in 120 mL glass jars using 200 g of oven-dried soil. The first set of ten (10) samples were used for measuring total suction by placing one 42.5 mm filter paper on a plastic screen above the dry soil surface. The second set of ten (10) samples was used for measuring matric suction by burying a 42.5 mm filter paper pressed between two 55.5 mm filter papers within an initially saturated soil. Saturation was achieved by adding the required amount of distilled water to the dry soil and allowing homogenization by sealing the glass jars. After 24 h, the jar lids were removed, and the soils were allowed to dry under ambient laboratory conditions (temperature of 19.6 °C ± 0.4 °C and relative humidity of 21.7% ± 6.5%).
Target gravimetric water contents of 40% to 1% with ten equal increments were selected to capture the entire range of saturated–unsaturated soil behavior. At the desired water content, the samples were stored inside an insulated box for 30 days to ensure equilibration of filter paper for water content [45]. Each jar was opened to remove the filter paper and the latter was rapidly sealed in a pre-weighed 60 mL metal container to determine the wet mass. Thereafter, the container was opened, and the filter paper was oven dried at 110°C for 12 h. The metal container along with the filter paper was re-sealed and placed on a metal cooling block for 120 s, following which the dry mass was determined.

4. Results and Discussion

4.1. Deformations during Low Demand Evaporation

Figure 4 presents three-dimensional soil models over the entire range of drying under ambient atmosphere (low demand). As expected, the silty sand (Figure 4a) exhibited negligible horizontal and surface area deformation. During the initial 8 h period, a water film was visible at the surface along with a small vertical deformation; no further deformation was observed thereafter. The 16 h observation shows a dark brown surface devoid of the water film. Generally (as observed in successive models), the soil gradually changed color to attain a light brown surface, thereby indicating the downward movement of the drying front.
The lean clay (Figure 4b) exhibited significant deformations which were primarily in the vertical direction up to 16 h and multi-directional thereafter. An initial thin water film (0 h) disappeared by the end of 4 h while the surface remained dark brown in colour. The 48-h observation shows an abrupt change in color to light brown, attributed to soil detachment from the cup walls due to the higher clay content, similar to [12], indicating the drying front had moved below the surface. This was observed during testing in the remainder of the soil models up to the 72-h period.
Figure 5 gives the various types of deformations versus water content for the investigated soils. Horizontal deformation ( D d , Figure 5a) was negligible for silty sand, whereas it comprised three parts for lean clay, namely; no increase up to 25% w, sharp increase of about 6% when the sample pulled away from the cup sides, thereby increasing the exposed area for water escape between 25% w and 18% w, and a low increase of 1% thereafter. In contrast, vertical deformation ( D h , Figure 5b) was found to linearly increase to 6% for both soils up to 31 ± 1% w such that it remained unchanged (horizontal line) for silty sand and gradually increased to reach a total of 13% for lean clay. The gradual D h increase in lean clay is attributed to its higher water adsorption and retention characteristics as observed by [46]. Surface area deformation ( D s , Figure 5c) closely followed D d , indicating no change for silty sand and the three zones of change reached up to a 70% increase for lean clay, following a similar pattern as found by [47]. Finally, volumetric deformation ( D v , Figure 5d) was similar to D h and showed 6% volume reduction for silty sand and 17% for lean clay, similarly observed by [48].

4.2. Low Demand Evaporation, Water Retention, and Soil Shrinkage

Figure 6 presents the behaviour of silty sand under low atmospheric demand in terms of evaporation, WRC, and SSC, with respect to gravimetric water content (w), volumetric water content (θ), and degree of saturation (S). The parameters on the x-axis have the following significance: gravimetric water content is the most accurate because it is based on direct measurements, volumetric water content is important for agricultural purposes in terms of water demand and supply, and degree of saturation is critical to understand desiccation from a geotechnical engineering perspective [29]. Stage I and Stage V were not captured in the evaporation tests and, as such, the evaporative flux comprised a pattern comparable to [19], whereby Stage II shows a decrease from 31 mg/m2∙s (38% w, 50% θ and 100% S) to 25 mg/m2∙s (30% w, 43% θ, and 93% S ) , followed by Stage III with a constant flux of 25 mg/m2∙s until 15% w, 21% θ, and 45% S, and then by Stage IV with a decrease up to 11 mg/m2∙s, (4% w, 6% θ, and 13% S).
The WRC included matric suction and total suction. The matric suction followed the typical trend, showing no change up to the AEV (1 kPa) followed by a sharp decline up to the RSV (100 kPa) and then by a flat line up to a completely dry state. The total suction remained constant at 100 kPa up to 10% w, 14% θ, and 30% S, and gradually increased thereafter to merge with matric suction close to the boundary between Stage II and Stage III. The gradual convergence of matric and total suction in Stage IV is attributed to the diminishing osmotic suction at low water contents [49]. This presence of osmotic suction, which contributed to the measured total suction, is related to ions in distilled water and calcite release from the silty sand [50]. The effect of osmotic suction could not be captured in the SSC that exhibited a J-shaped curve, comprising a significant void ratio decrease (1.04 to 0.86) within Stage II and remaining constant through the remainder of the evaporation stages.
Figure 7 presents the behaviour of lean clay under low atmospheric demand. Again, the evaporative flux showed the three stages, with a more pronounced Stage II showing a decrease from 34 mg/m2∙s (37% w, 49% θ, and 95% S) to 14 mg/m2∙s (17% w, 28% θ, and 65% S). This is attributed to the linear volume decrease in the soil (Figure 5d). Stage III showed a small decrease to 13 mg/m2∙s flux (10% w, 15% θ, and 35% S). Finally, evaporative flux from the lean clay ended in 3 mg/m2∙s (4% w, 6% θ, and 13% S) in Stage IV. This behavior is similar to the silty sand because of the negligible volume decrease (Figure 5d).
The matric suction showed negligible change up to the AEV (5 kPa) followed by a gradual decline up to the RSV (1400 kPa) and then by a straight line up to a completely dry state. The total suction was found to be constant at 70 kPa up to 17% w, 27% θ, and 63% S, and gradually increased to closely match matric suction around the boundary between Stage II and Stage III. The presence of osmotic suction is related to ions in distilled water and dolomite dissolution from the lean clay [39]. Furthermore, the SSC showed a significant void ratio decrease (1.07 to 0.78) in Stage II, marginal decrease (0.78 to 0.73) in Stage III, and no decrease (0.73) in Stage IV.

4.3. High Demand Evaporation

Figure 8 provides the evaporative fluxes under high demand. The first data point for silty sand (Figure 8a) at 27% w could not be shown owing to the easy escape of water during sample transfer to different equipment. This may have resulted in the absence of Stage II in silty sand. In Stage III, a constant flux of 200 mg/m2∙s over a range of 28% w to 23% w was observed whereas in Stage IV a linear decrease up to 45 mg/m2∙s was seen reaching 12% w. In contrast, the lean clay (Figure 8b) retained enough water during sample preparation such that the initial points were measured. Evaporative flux comprised Stage II showing a sharp decrease from 260 mg/m2∙s (28% w) to 150 mg/m2∙s (22% w ) , followed by Stage III with a moderate decrease to 100 mg/m2∙s until 14% w, and then by Stage IV with a decrease up to 30 mg/m2∙s (8% w). The range of water content for Stage III was found to decrease under high demand when compared with that under low demand, as reported by [5]. The slope of Stage IV was found to be about the same for both soils, similar to the findings given in [21], and tended to approach the value obtained for low demand. For both soils, the observed stages have shifted rightwards such that these cover a larger range of water content when compared with those under low demand. For the investigated range of water content, the total water loss under high demand was found to be 7 times that under low demand.

5. Summary and Conclusions

Sustainable farming requires a clear understanding of the effect of desaturation and shrinkage on evaporative losses from soils. Laboratory tests were conducted on a silty sand and a lean clay under low demand and high demand atmospheric conditions. The main conclusions of this study are given as follows:
  • The downward movement of the drying front was gradual in the silty sand between 0 h and 40 h whereas that in the lean clay was abrupt between 40 h and 48 h. Over the investigated range of water content, the surface area did not change for silty sand and increased up to 70% for lean clay. The corresponding volume reductions were found to be 6% and 17%, respectively.
  • The evaporative flux for silty sand comprised a decrease from 31 to 25 mg/m2∙s in Stage II, followed by a constant flux during Stage III, and a decrease up to 11 mg/m2∙s in Stage IV. This soil exhibited low AEV (1 kPa) and RSV (100 kPa) and the total suction was found to merge with the with matric suction at Stage II-Stage III boundary. The SSC was J-shaped, with the only void ratio decrease in Stage II.
  • The evaporative flux for lean clay had a longer Stage II (34 to 14 mg/m2∙s), a near constant Stage III, and similar Stage IV (13 to 3 mg/m2∙s). With higher AEV (5 kPa) and RSV (1400 kPa), this soil showed a similar merger of total suction and matric suction at Stage II-Stage III boundary. The SSC showed a significant void ratio decrease in Stage II, marginal decrease in Stage III, and no decrease in Stage IV.
  • Under high demand, the silty sand exhibited Stage III and Stage IV evaporation whereas the lean clay also showed significant flux during Stage II. The slope of Stage IV was found to be identical for both soils and approached the value obtained for low demand. For the investigated range of water content, the total water loss under high demand was found to be 7 times that under low demand.

Author Contributions

Data curation and analysis, J.S.; Supervision, S.A.; Writing—original draft, J.S.; Writing—review & editing, S.A. All authors have read and agreed to the published version of the manuscript.

Funding

This research was funded by Natural Science and Engineering Research Council of Canada.

Institutional Review Board Statement

Not applicable.

Informed Consent Statement

Not applicable.

Data Availability Statement

The authors can provide access to test data upon request.

Acknowledgments

The authors would like to thank the University of Regina for providing laboratory space.

Conflicts of Interest

The authors declare there is no conflict of interest.

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Figure 1. Conceptual correlations for an inert soil under low atmospheric demand, including: (a) evaporation stages, (b) water retention curve, and (c) soil shrinkage curve.
Figure 1. Conceptual correlations for an inert soil under low atmospheric demand, including: (a) evaporation stages, (b) water retention curve, and (c) soil shrinkage curve.
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Figure 2. Grain size distributions of the investigated soils.
Figure 2. Grain size distributions of the investigated soils.
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Figure 3. Stages of soil preparation: (a) oven dried and unconsolidated soil, (b) dry soil tamped down and levelled with cup, (c) swelling 12 hours after saturation, and (d) wet soil tamped down.
Figure 3. Stages of soil preparation: (a) oven dried and unconsolidated soil, (b) dry soil tamped down and levelled with cup, (c) swelling 12 hours after saturation, and (d) wet soil tamped down.
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Figure 4. Three-dimensional models of the investigated soils during drying under laboratory ambient conditions: (a) silty sand; and (b) lean clay.
Figure 4. Three-dimensional models of the investigated soils during drying under laboratory ambient conditions: (a) silty sand; and (b) lean clay.
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Figure 5. Deformations during drying under low demand for silty sand and lean clay: (a) horizontal deformation; (b) vertical deformation; (c) surface area deformation; (d) volume deformation.
Figure 5. Deformations during drying under low demand for silty sand and lean clay: (a) horizontal deformation; (b) vertical deformation; (c) surface area deformation; (d) volume deformation.
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Figure 6. Behavior of silty sand under low atmospheric demand.
Figure 6. Behavior of silty sand under low atmospheric demand.
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Figure 7. Behavior of lean clay under low atmospheric demand.
Figure 7. Behavior of lean clay under low atmospheric demand.
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Figure 8. Evaporative flux under high demand for (a) silty sand and (b) lean clay.
Figure 8. Evaporative flux under high demand for (a) silty sand and (b) lean clay.
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Table 1. Summary of index properties for soil classification.
Table 1. Summary of index properties for soil classification.
Index PropertyASTMSilty SandLean Clay
Specific   Gravity ,   G s D854-142.662.69
Material Finer than 4.75 mm (%)D6913-1710099
Material Finer than 0.075 mm (%)D6913-171962
Material Finer than 0.002 mm (%)D7928-21531
Liquid   Limit ,   w l (%)D4318-17e12732
Plastic   Limit ,   w p (%)D4318-17e12518
Plasticity   Index ,   I p (%)D4318-17e1214
Shrinkage   Limit ,   w s (%)--14
USCS SymbolD2487-17SMCL
Table 2. Summary of initial conditions of soil samples.
Table 2. Summary of initial conditions of soil samples.
Index PropertyASTMSilty SandLean Clay
Low Demand
Water Content, w (%)D2216-193940
Dry   Density ,   ρ d (g∙cm−3)-1.301.30
Void   Ratio ,   e -1.041.07
Degree of Saturation 1, S-100100
Volumetric   Water   Content   2 ,   θ -5152
High Demand
Water Content, w (%)D2216-192727
Dry   Density ,   ρ d (g∙cm−3)-1.301.30
Void   Ratio ,   e -1.041.07
Degree of Saturation 1, S-6967
Volumetric   Water   Content   2 ,   θ -3535
1  S = w · G s / e ; 2  θ = w · γ d / γ w .
Table 3. Summary of measured atmospheric and surface parameters.
Table 3. Summary of measured atmospheric and surface parameters.
ParameterUnitSymbolSurface and Atmospheric Condition
Silty SandLean Clay
Low
Demand
High
Demand
Low
Demand
High
Demand
Data Point Count n8653216187162161
Atmosphere
Momentum
Air Velocitym/s v <0.11.3<0.11.3
Air PressurePa e a 95640939409617092901
Relative Humidity% h U L 28.655.425.755.5
Energy
Temperature°C T a U L 21.318.921.418.9
Shortwave Flux (↓)W/m2 S i 03250325
Surface
Energy
Shortwave Flux (↑)W/m2 S o 0101
Temperature°C T s -22.1-22.0
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Suchan, J.; Azam, S. Influence of Desaturation and Shrinkage on Evaporative Flux from Soils. Geotechnics 2022, 2, 412-426. https://0-doi-org.brum.beds.ac.uk/10.3390/geotechnics2020019

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Suchan J, Azam S. Influence of Desaturation and Shrinkage on Evaporative Flux from Soils. Geotechnics. 2022; 2(2):412-426. https://0-doi-org.brum.beds.ac.uk/10.3390/geotechnics2020019

Chicago/Turabian Style

Suchan, Jared, and Shahid Azam. 2022. "Influence of Desaturation and Shrinkage on Evaporative Flux from Soils" Geotechnics 2, no. 2: 412-426. https://0-doi-org.brum.beds.ac.uk/10.3390/geotechnics2020019

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