Increase In Volumetric Water Content Research Articles

Thawing process of high-ice-content frozen soil subjected to saturated steam

Engineering measures based on permafrost protection to inhibit high-ice-content permafrost thawing and subsidence in some areas of the Qinghai-Tibetan Plateau (QTP) are challenging owing to global warming. Hence, early permafrost thawing is an effective method for reducing the later settlement of the upper infrastructure. Saturated steam can thaw permafrost rapidly, but the research on the process and mechanisms of thawing permafrost with steam is lacking. In this study, steam-thawing tests were conducted on four types of frozen soil with high ice contents (20 %, 30 %, 40 %, and 50 % by volume). The temporal and spatial migration patterns of temperature and moisture in permafrost subjected to steam and the resulting thawing rates were analyzed by real-time monitoring of temperature and the volumetric water content (VWC) during the thawing process. Based on this, the mechanism of steam thawing permafrost was analyzed. The results showed that the continuous injection of saturated steam into the permafrost for 2 h resulted in complete thawing of permafrost with all four ice-contents, but the thawing rates were significantly different. The injection of steam led to an increase in VWC of thawed soil within a 5 cm radius by 1.26–1.68 times. The thawing of permafrost at different ranges was dominated by two different modes, pressure-driven water steam migration leading to permafrost thawing at a radius of about 10 cm and thawing of permafrost at the rest of the range by hydrothermal migration induced by temperature and humidity gradient. Compared to other conventional thawing methods, steam thawing is more suitable for targeted pre-thawing of deeply permafrost layers with high ice content.

Experimental Study on Pore Structure and Soil-Water Characteristic Curve of Ionic Rare Earth Ore under Seepage

The ionic rare earth (RE) ore body undergoes particle transport and pore structure change during the leaching process, resulting in "uneven percolation, preferential channel, leaching blind area," and other problems, leading to structural changes in the ore body, low leaching efficiency, and waste of resources. The unsaturated infiltration process is also the key stage that causes these problems. The initial pore structure evolution of the ore body plays a decisive role in the permeability coefficient of the ore body, and the direct influencing factor of the permeability coefficient is the distribution of the pore radius. We carried out research through indoor simulated leaching, the filter paper method for determining matrix suction, and nuclear magnetic resonance (NMR) testing. An ionic rare earth ore soil-water characteristic curve within a large matrix suction range was obtained by the filter paper method. With the increase in volumetric water content, the matrix suction presents a sharp downward trend. When the volumetric water content is less than 20%, this rule is particularly obvious. With the increase in matrix suction, the thickness of the adsorbed water film on the particle surface and pore radius show a decreasing power function trend. Under percolation, the porosity of an ionic rare earth ore sample tends to increase linearly with the increase in volumetric water content during the process from non-saturation to saturation; the porosity of a saturated ore sample after seepage expanded by 17.5 times compared to that of an unsaturated ore sample before seepage. The change rule of the internal microstructure of the ore sample is reflected in the gradual disappearance of micro pores and the gradual formation of small, medium, large, and mega pores, which shows a gradual increase trend. In the pore radius distribution, the more large and medium pores, the larger the permeability coefficient; the more micro and small pores, the smaller the permeability coefficient. For some ore bodies with poor permeability, the ore body is infiltrated with clear water under small water pressure before leaching with a leaching solution, which can improve the permeability of the ore body, effectively improve the efficiency of rare earth leaching, and increase the economic benefits.

A Trans-Scale Study on the Influence of Water Content and Particle Size on Matric Suction

Exploring the water retention properties of unsaturated soil from the perspective of a liquid bridge has been a popular issue in recent years. This study first measures the soil–water characteristic curves (SWCCs) of granular specimens to determine the influence of particle size on matric suction from a macroscopic perspective. Then, the internal mechanism of the influence of particle size and volumetric water content on matric suction is analyzed from the mesoscopic perspective by using the Young–Laplace (Y–L) equation to calculate matric suction between two equal spheres. The macroscopic and mesoscopic experiments both show that matric suction decreases with an increase in particle radius. Moreover, identifying the internal mechanism of SWCC from the liquid bridge perspective is only applicable when the influence of gravity can be disregarded or is in the transitional stage. The influence of volumetric water content and sphere radius on matric suction is mostly caused by the variation in the outer radius of the liquid bridge ( r 1 ) and the neck radius of the liquid bridge ( r 2 ). With an increase in volumetric water content and sphere diameter, the increasing rate of r 1 is much higher than r 2 , and the macroscopical matric suction gradually decreases.

Physical Modelling of Rainfall-Induced Sandy and Clay-Like Slope Failures

Small-scale slope modelling was performed to evaluate the failure process of a landslide triggered by artificial rainfall. The model platform 2.3 m long, 1.0 m wide, and 0.5 m deep was used to build small-scale slope models with the same geometric conditions but different soil types/materials, including sand and two sand-kaolin mixtures with the same slope angle. The hydraulic response of the slope models under simulated rainfall conditions was monitored using volumetric water content, pore water pressure, and matric suction sensors installed at different depths and along different profiles. Slope surface deformation and failure development was also monitored. This paper discusses the factors affecting landslide initiation and propagation, and their relationship to the slope material, infiltration process, and overall soil resistance in a slope related to soil strength, effective stress, and matric suction contribution in the unsaturated part of the slope. Rainfall infiltration caused increase of volumetric water content, dissipation of suction in initially partially saturated materials of the small-scale slope models, resulting in a decrease in effective stresses and shear strength, which in turn led to the occurrence of movements and initiation of slope failures. The main observations arising from the results of the conducted tests relate to initiation and development of the observed instabilities of sandy and clay-like slopes. The test results have shown that within the slopes built from clean sand failure occurs due to groundwater level rising at the slope foot and further retrogressive failure towards the top of the slope, while in the slopes built from sand-kaolin mixtures, instabilities occur in the form of cracks in unsaturated conditions and are the result of matric suction dissipation due to rainfall infiltration.

Effects of Slow Pyrolysis Biochar on CO2 Emissions from Two Soils under Anaerobic Conditions

The amendment of sandy Haplic Arenosol and clayey loam Gleyic Fluvisol with two rates of biochar derived from the slow pyrolysis of wood feedstock was evaluated under anaerobic conditions in a 63-day laboratory experiment. The rates of biochar were 15 and 30 t ha−1. Both rates of biochar were applied either with or without 90 kg ha−1 of nitrogen fertilizer (NH4NO3). Soils with no amendments were used as control treatments. Our results showed that only the incorporation of 15 t ha−1 of biochar, compared with the control treatment, led to a significant (p < 0.05) increase in volumetric water content of the sandy soil and a significant (p < 0.05) decrease in the parameters of the clayey loam soil. Increasing the biochar rate from 15 to 30 t ha−1 did not result in significant changes in volumetric water content in either type of soil. In the sandy soil, CO2 emissions were significantly (p < 0.05) higher in the treatments of 15 and 30 t ha−1 with N fertilizer compared with the control and N fertilizer treatment. In the clayey loam soil, the combined application of both rates of biochar with N fertilizer caused no significant increase in CO2 emissions compared with the control and N fertilizer treatment. The incorporation of 30 t ha−1 of biochar into the sandy soil contributed to a significant (p < 0.01) increase in the cumulative CO2 flux compared with the control treatment. Application of 15 and 30 t ha−1 of biochar into the clayey loam soil led, respectively, to a significant (p < 0.05) and a nonsignificant increase in the cumulative CO2 fluxes compared with the control treatment.

Pre-sprouted Sugarcane Plantlets Produced in Ebb-and-flow Subirrigation Automated by Soil Moisture Sensors

There is a growing demand for innovation in the sugarcane production chain to increase crop productivity. The recent use of sugarcane plantlets to improve planting efficiency in the field is a viable option, and nurseries are seeking for enhanced irrigation systems to accelerate the production of high-quality plantlets and optimize water and fertilizer inputs. This research aimed to determine the adequate substrate volumetric water content (VWC) to produce pre-sprouted sugarcane plantlets using ebb-and-flow subirrigation automated by soil moisture sensors and the effects on plant growth in greenhouse on acclimation stages #1 and #2. We tested three thresholds to trigger subirrigation automatically when sensor readings dropped below the setpoints: VWC 45% (v/v), VWC 35%, and VWC 25%. Plantlets were cultivated in 54-cell flat trays with 130-cm3 cone-shaped containers filled with commercial substrate in ebb-and-flow benches controlled by capacitive soil moisture sensors connected to a datalogger. The results indicated the automated subirrigation system worked properly, successfully irrigating the plantlets based on the target VWC. VWC 35% was the most efficient treatment, reducing fertilizer solution consumption in 44.78% (368.47 L and 2.41 mm d−1) in comparison with VWC 45% (667.28 L and 4.37 mm d−1) and increasing water use efficiency in 43.18% (7.62 g L−1) when compared to VWC 45% (4.33 g L−1), which produced less biomass with the same amount of water. VWC 45% treatment also resulted in the highest number of irrigation events, with the greatest electrical conductivity value in the substrate at the end of the experiment. All plant growth variables such as stem diameter, plant height, first ligule height, and shoot and root dry weight responded positively to the increase in VWC (P < 0.05). VWC 45% resulted in the highest biomass except root dry weight where VWC 35% was superior. VWC 35% was statistically the same to VWC 45% in all biometric responses (P < 0.05) and showed the best efficiency rate in fertilizer solution consumption and water use. Based on our results, we recommended VWC 35% as the setpoint for water management to produce pre-sprouted plantlets using automated ebb-and-flow subirrigation.

A protective measure for expansive soil slopes based on moisture content control

For expansive soil slopes, the primary failure mode is surface- or shallow-layer slide, which can occur easily under repeated rainfalls. In this investigation, a field testing program is implemented on five expansive soil slopes with different inclination subjected to artificial rainfalls, against which a numerical model is calibrated. Hydro-mechanical analysis is then conducted to estimate the factor of safety for expansive soil slopes with different pattern of fissures. A high slope inclination can increase the surface runoff, although the factor of safety decreases. It is of significance to minimize the amount of rainfall infiltration through desiccation cracks, since the increase in volumetric water content from rainfall events is more detrimental to reduce the unsaturated shear strength of soil. A conceptual framework is proposed to apply a drip irrigation system for expansive soil slopes. The volumetric water content can be maintained above a critical level to avoid the initiation of desiccation cracks. In the end, design parameters for the drip irrigation system are optimized.

Physical model experiments for shallow failure in rainfall-triggered loess slope, Northwest China

In order to effectively reduce the impact of rainfall-induced landslides on properties and life, it is important to understand rainfall-caused landslides and their sliding mechanisms. The objective of this paper is to study the effects of different rainfall patterns and different slope structures on the deformation and failure process of shallow loess slopes. To achieve the objective, three categories of indoor physical model experiments of a loess slope with and without a vertical joint were implemented under different rainfall patterns. Three kinds of sensors, including volumetric water content, matric suction, and pore-water pressure sensors, were buried in the model slopes to record the internal changes driving deformation. Analyses of the sensor records and the associated deformational changes, and the experimental results under different conditions show that the matric suction in loess slopes decreased gradually. Loess strength reduced with the continuous increase of volumetric water content. After excess pore-water pressure was generated by the slope deformation and poor drainage of the loess, it decreased the effective stress and the loess strength, which resulted in landslides. In addition, it was observed that the influence of slope structure on stability was greater than that of rainfall patterns. This paper attempts to explain the failure mode and triggering mechanisms of shallow loess landslides induced by rainfall.

Effect of Soil Types on The Development of Matric Suction and Volumetric Water Content for Dike Embankment During Overtopping Tests

The resistance of dike materials has a great effect on the development of hydraulic engineering around the world. It helps to understand the mechanism of dike failure occurred due to the influence of hydraulics and Geotechnical parameters. The overtopping moment is one of the main failures that reduces the stability of the dike embankment through initiating the breach channel inside dike crest as a result of water flow above the downstream slope of the dike. Two spatial overtopping tests were conducted at in Hydraulic Geotechnical laboratories at the University Sains of Malaysia to observe the evolution of matric suction and volumetric water content for two soil types of sand and very silty sand soils. A pilot channel was cut in dike crest along the side wall of the small flume channel to represent the transition water flow from upstream into downstream slopes during overtopping test. The results indicated that the matric suction decreases due to the increase of volumetric water content during the saturation of dike body. The proportion increasing and decreasing of volumetric water content and matric suction is lower in very silty sand than those in sand soil due to the presence of fine particles in previous soil.

Characterization of unsaturated diffusivity of tight sandstones using neutron radiography

Water flow in unsaturated tight sandstones plays a significant role in the area of the secondary and enhanced hydrocarbon recovery as well as the geological storage of carbon dioxide and nuclear wastes. Although a few non-destructive techniques, such as nuclear magnetic resonance, magnetic resonance imaging and X-ray imaging, can be used to capture fluid transport in sub-micron pores, great challenges exist due to the presence of iron or the use of the contrast agents (e.g. cesium chloride and salts), resulting in inaccurate results or alteration of the wetting behavior of the porous media. In addition, models for describing diffusivity and water transport in unsaturated tight sandstones are also limited. In this work, the neutron radiography facility at China Advanced Research Reactor was used to determine water content profiles during the water imbibition in two types of tight sandstones: silty sandstone and coarse grained sandstone. The diffusivity was determined separately by three methods, including Matano’s method, Meyer-Warwick method and a fractal method, which was introduced as probably the first attempt to relate the microstructure observed by the high resolution X-ray computed tomography (CT) with the unsaturated diffusivity function for the tested tight sandstones. The air-entry value and the fractal dimension used in the fractal model were calculated based on the results of mercury intrusion porosimetry and CT data, respectively. The results from neutron images illustrate that the fractal model can give a reasonable description of the diffusivity function for the tested sandstones. Meyer-Warwick model produces a little bit higher diffusivity value at low water content range. The fractal model works better for the silty sandstone. Results also show that the value of water diffusivity increases with the increase in volumetric water content for both tested tight sandstones. This work shows that neutron radiography offers a feasible and more reliable way for characterizing fluid flow in other tight geo-materials and the fractal model also provides an easier way to give a quantitative description of the diffusivity than the core-flooding or centrifuge drainage experiment.

Analysis of Infiltration-Suction Response in Unsaturated Residual Soil Slope in Gelugor, Penang

Rainfall infiltration on residual soil slope may impair slope stability by altering the pore-water pressure in the soil. A study has been carried out on unsaturated residual soil slope in Gelugor, Penang to determine the changes in matric suction of residual soils at different depth due to rainwater infiltration. The sequence of this study includes the site investigation, field instrumentation, laboratory experiment and numerical modeling. Void ratio and porosity of soil were found to be decreasing with depth while the bulk density and dry density of soil increased due to lower porosity of soil at greater depth. Soil infiltration rate and matric suction of all depths decrease with the increase of volumetric water content as well as the degree of saturation. Numerical modeling was used to verify and predict the relationship between infiltration-suction response and degree of saturation. Numerical models can be used to integrate the rainfall scenarios into quantitative landslide hazard assessments. Thus, development plans and mitigation measures can be designed for estimated impacts from hazard assessments based on collected data.

Biofilm effect on soil hydraulic properties: Experimental investigation using soil‐grown real biofilm

AbstractUnderstanding the influence of attached microbial biomass on water flow in variably saturated soils is crucial for many engineered flow systems. So far, the investigation of the effects of microbial biomass has been mainly limited to water‐saturated systems. We have assessed the influence of biofilms on the soil hydraulic properties under variably saturated conditions. A sandy soil was incubated with Pseudomonas Putida and the hydraulic properties of the incubated soil were determined by a combination of methods. Our results show a stronger soil water retention in the inoculated soil as compared to the control. The increase in volumetric water content reaches approximately 0.015 cm3 cm−3 but is only moderately correlated with the carbon deficit, a proxy for biofilm quantity, and less with the cell viable counts. The presence of biofilm reduced the saturated hydraulic conductivity of the soil by up to one order of magnitude. Under unsaturated conditions, the hydraulic conductivity was only reduced by a factor of four. This means that relative water conductance in biofilm‐affected soils is higher compared to the clean soil at low water contents, and that the unsaturated hydraulic conductivity curve of biofilm‐affected soil cannot be predicted by simply scaling the saturated hydraulic conductivity. A flexible parameterization of the soil hydraulic functions accounting for capillary and noncapillary flow was needed to adequately describe the observed properties over the entire wetness range. More research is needed to address the exact flow mechanisms in biofilm‐affected, unsaturated soil and how they are related to effective system properties.

Numerical analysis of buried pipes under field geo-environmental conditions

Buried pipes are vital infrastructures and are mostly used to transport energy and other essential commodities. These pipes are generally buried within the top layer of soil deposits, and therefore, are highly affected by different geo-environmental conditions. In this paper, a modeling approach is introduced for the analysis of buried pipelines through real-life scenarios. The model provided reasonable estimates for the elastic deformations of a soil-pipe system under different soil and loading conditions. The model was then used to address the performance of a hypothetical pipeline buried in an unsaturated clay soil. The modeling analysis captured the pipe displacements that occurred due to the change in soil suction associated with changes in the soil moisture content. The soil suction was estimated based on field measurements, and was, then used as an input to the model. The change in volumetric water content in the area studied was found to be as low as 5 %, as high as 20 %, and corresponded well with the seasonal variation in climate conditions. Direct correlations between the change in soil moisture content and the resulting pipe displacements were developed. The results indicated that normalized pipe displacements up to 6 % occurred due to the relative increase in volumetric water content of 20 % representing the change from the field condition to full saturation. The magnitude of pipe displacements increased significantly with the decrease of the pipe depth within the active soil zone.

Subirrigation automated by capacitance sensors for salvia production

Subirrigation is typically controlled using timers to periodically irrigate plants based on a pre-determined schedule. The objective of this study was to evaluate the usefulness of capacitance-type sensors to monitor substrate water content and to control subirrigation automatically for salvia production in greenhouse. Additionally, we quantified the effect of different substrate volumetric water content (VWC) on growth of plants cultivated in 15-cm diameter × 13.75-cm height pots. Automation was performed using three EC-5 capacitance soil moisture sensors per experimental unit, connected to a system with a CR10X data logger, AM16/32 multiplexer, SDM-CD16AC relay driver and NK-2 submersible pumps. Substrate moisture readings were taken every 15 minutes, and plants were irrigated only if the readings dropped below pre-set VWC thresholds. We evaluated five levels of substrate VWC (0.1, 0.2, 0.3, 0.4 and 0.5 m3 m-3), with two replications, in a completely randomized design. The system effectively monitored and recorded VWC, and controlled irrigation accordingly. Substrate VWC ranged from 0.1 to 0.41, 0.2 to 0.39, 0.3 to 0.41, 0.4 to 0.43 and 0.5 to 0.53 m3 m-3, in ascending order of the treatments, with the highest values recorded after irrigation events. The number of irrigation events, total volume of nutrient solution applied, net photosynthesis, dry weight, number of branches and leaves, shoot height, leaf area, canopy light interception, and leaf chlorophyll content all increased significantly with the increase in VWC (p&lt;0.0001). The VWC of 0.5 m3m-3 provided the highest plant growth (p&lt;0.0001). Capacitance sensors can be used to both monitor soil moisture and control subirrigation for salvia production in soilless substrate, reducing the possibility of water stress caused by daily irrigation schedule using timers.

Effects of infiltration and evaporation on geosynthetic capillary barrier performance

This study includes an experimental investigation of the transient movement of water in unsaturated soil layers underlain by a geocomposite drainage layer (GDL) during cycles of infiltration and evaporation. The distribution in volumetric water content with depth in a soil column having a height of 1350 mm underlain by a GDL was measured during transient infiltration. The capillary break effect was observed to affect the soil up to a height of 500 mm above the GDL, with an increase in volumetric water content up to 20% above that expected for the case of infiltration under a unit hydraulic gradient. Due to the long duration of this test (2000 h), a shorter 150 mm high soil column was also evaluated to investigate the soil–GDL hydraulic interaction during cycles of infiltration and evaporation. The capillary break was observed to have re-established itself after infiltration was stopped and the soil near the interface dried. The suction and volumetric water content measured in the soil at breakthrough were consistent after multiple cycles of wetting and drying. The conditions in the soil after each breakthrough event corresponded to the point on the drying-path water retention curve of the nonwoven geotextile where it transitioned from residual to saturated conditions.

Characterizing water-level changes due to fracturing generated by the strike-slip fault of the 12 November 1999, Düzce, Turkey, earthquake using the VLF method

The devastating Duzce earthquake occurred on 12 November 1999 in Turkey, and caused groundwater pollution by damaging sewer systems in populated areas as well as pipelines and chemical plants. Leakage from these sources of pollutants advected and diffused along the hydraulic gradient enhanced by the surface rupture. We constructed a conceptual model to identify the flow system within and near the ruptured zone in the devastated town of Kaynasli by utilizing the very low-frequency electromagnetic induction (VLF) and dc-resistivity methods ten days after the earthquake. Void volume increase due to fracturing from the surface to a depth of several meters caused gravity-driven drainage to form a dewatered zone near the surface. This downward flow filled the fractures beneath the dewatered zone and caused an increase in volumetric water content. The measured apparent dc-resistivity profile with an electrode spacing of 5 m showed an increasing resistivity over the dewatered zone. The measured VLF profile, on the other hand, showed a characteristic behavior with decreasing resistivity corresponding to a depth where volumetric water-content increase is expected to occur.