Soil-water Mixture Research Articles

The role of soil dispersivity and initial moisture content in splash erosion: Findings from consecutive single-drop splash tests

Dispersive soil is commonly associated with hydraulic erosion due to its tendency to disperse when in contact with water. Nevertheless, the erosion process of dispersive soil remains poorly understood. This study aims to explore the influence of dispersivity and initial moisture content on the splash erosion of dispersive soil, which is a crucial stage of hydraulic erosion. Consecutive single-drop splash tests were conducted on artificially prepared dispersive soil (made by adding sodium carbonate to the soil) with varying dispersivity levels and moisture contents. A high-speed and a single-lens reflex (SLR) camera were employed to capture the process of erosion in exquisite detail. The results demonstrated the significant influence of dispersivity on splash erosion. At moisture content below 20%, increased dispersivity weakened the splash erosion effect, leading to reduced infiltration, splashed soil mass, crater volume, and depth. Conversely, when the initial moisture content reached 20% or saturation, intensified dispersivity exacerbated splash erosion. Dispersivity also increased the sensitivity of the soil splash process to changes in moisture content. Dispersive soil exhibited greater sensitivity compared to non-dispersive soil, affecting the mass of splashed soil, soil-water mixture droplets area, water-soil mass ratio, and particle ejection distance. Dispersivity also caused splashed particles to fragment, resulting in more soil-water mixture droplets and a greater splash distance. Furthermore, dispersivity reduced infiltration ratio and increased runoff yield after erosion events, indicating a higher risk of transporting splashed soil particles through runoff. These insights contribute to erosion models and have practical applications in managing dispersive soil.

Variability in the Hydrological Processes of Six Typical Woodlands Based on Stable Isotopes in Subtropical Regions in Central China

Changes in woodland characteristics induced by plants and soil greatly affect soil hydrological processes. Stable isotope technology and indoor soil moisture characteristic experiments were conducted at three rainfall levels (3.6, 23.5, and 49.8 mm) to investigate the hydrological processes under six woodlands (two pure forests and four mixed forests). The main influencing factors contributing to these changes were identified in a low mountain and hilly region in central China. The soil waterline equation in this area was soil water δD = 5.626 δ18O − 16.791 (R2 = 0.798). The slope and intercept in the soil waterline equation were smaller than the atmospheric waterline equation. From a temporal perspective, the soil moisture content varied in the same trend under different rainfall events, with the maximum and minimum values on the first day after rainfall and the day before rainfall, respectively. However, an overall trend that first increased and then decreased was observed. From a spatial perspective, the soil moisture content increased with soil depth, and the increase rate was in the order of 0–20 cm and 20–40 cm in different soil layers. The soil moisture content in mixed conifer broadleaved woodlands was high. The soil water δD and δ18O in mixed conifer broadleaved woodlands and underground soil were relatively depleted. The effects of soil water-holding capacity, particle size composition, slope, canopy closure, and other factors on soil hydraulic parameters were comprehensively analyzed. The results showed that the extremely coarse sand (1–2 mm) particle content was the main parameter affecting soil-saturated hydraulic conductivity Ks, whereas the slope was the main factor affecting soil water δD and δ18O. In needle-leaved forests, the soil water infiltration form was a rainwater and soil water mixture downward diffusion, whereas the rainwater replaced the original soil water in the needle and mixed conifer broadleaved forests.

A deep learning approach for rapid detection of soil liquefaction using time–frequency images

Soil liquefaction – a common hazard during earthquakes – can cause severe damage to infrastructure systems. The excessive pore water pressure induced by underground shaking can result in a sudden loss of soil stiffness and strength, which renders the soil–water mixture to behave temporarily as “liquid”. Identifying liquefaction events and extracting their time of initiation and duration from recorded data are critical capabilities for validating and improving predictive models, and ultimately, effectively mitigating this hazard. The current approach is to conduct on-site investigations or simplified statistical analyses, which are generally time-consuming and bear high uncertainties, except for the most obvious cases. In this study, we utilize a convolutional neural network (CNN), a deep learning method, to predict both the occurrence of a liquefaction event and its triggering time (if it occurred). For this purpose, first, more than one million high-fidelity nonlinear site response simulations with different soil profiles and ground motions are performed. The surface acceleration time-histories are then converted into time–frequency distribution images, which are fed into a CNN as the training inputs. The trained CNN exhibits high prediction accuracy for both training and validation sets, another suite of independent site response simulations, as well as real-life earthquake data.

Two-Phase Two-Layer Depth-Integrated SPH-FD Model: Application to Lahars and Debris Flows

The complex nature of debris flows suggests that the pore-water pressure evolution and dewatering of a flowing mass caused by the high permeability of soil or terrain could play an essential role in the dynamics behavior of fast landslides. Dewatering causes desaturation, reducing the pore-water pressure and improving the shear strength of liquefied soils. A new approach to landslide propagation modeling considering the dewatering of a mass debris flow has drawn research attention. The problem is characterized by a transition from saturated to unsaturated soil. This paper aims to address this scientific gap. A depth-integrated model was developed to analyze the dewatering of landslides, in which, desaturation plays an important role in the dynamics behavior of the propagation. This study adopted an SPH numerical method to model landslide propagation consisting of pore-water and a soil skeleton in fully or partially saturated soils. In a two-phase model, the soil–water mixture was discretized and represented by two sets of SPH nodes carrying all field variables, such as velocity, displacement, and basal pore-water pressure. The pore-water was described by an additional set of balance equations to take into account its velocity. In the developed two-layer model, an upper desaturated layer and a lower saturated layer were considered to enhance the description of dewatering. This is the so-called two-phase two-layer formulation, which is capable of simulating the entire process of landslides propagation, including the large deformation of soils and corresponding pore-water pressure evolutions, where the effect of the dewatering in saturated soils is also taken into account. A dam-break problem was analyzed through the new and previously developed model. A flume test performed at Trondheim was also used to validate the proposed model by comparing the numerical results with measurements obtained from the experiment. Finally, the model was applied to simulate a real case lahar, which is an appropriate benchmark case used to examine the applicability of the developed model. The simulation results demonstrated that taking into account the effects of dewatering and the vital parameter of relative height is essential for the landslide propagation modeling of a desaturated flowing mass.

An analytical solution for heat extraction from shallow ground using a single-phase closed thermosyphon: A model for artificial ground freezing

Artificial ground freezing can be costly. Except for drilling and installation costs, they may also include maintenance and electricity consumption. What if there is a possibility to build an apparatus that naturally works without a need for external energy? Closed thermosyphons filled with a working fluid (antifreeze) that has a proper thermal conductivity can be the solution whether there is a need for heat extraction for a greenhouse area or an intention to freeze the ground artificially. A portion of a vertical closed pipe is installed in the soil while the other is in contact with the ambient air. The heat transfers from the high-temperature zone, soil, to the low-temperature zone, wellbore, and is released into the air. The results show that increasing the target depth underground from 1.5 m to 3.5 m increases the freezing time from 5 days to 24 days. Expanding the length outside of the ground (cooling) from 1.5 m to 3.5 m improves the heat transfer by 10 W, decreasing the freezing time by 2.5 days. A slight growth in diameter allows for a larger soil-water mixture to be involved in freezing, and thus the freezing time increase; however, since it enhances the heat transfer rate, a larger amount of freezing storage is obtained (e.g., an increase from 3.9 in. to 5.5 in. shows a 150-kJ growth at the end of 60 days). A decrease of 10 °C in air temperature also shows a staggering growth in freezing storage by >1500 kJ.

Effects of Equilibrium Time on Electrical Conductivity Measurements Using Soil-Water Extracts and Soil Saturated Paste

Electrical conductivity (EC) is a robust indicator of soil salinity. In South Korea, EC of 1:5 of soil:water extracts (EC1:5) and soil saturated paste extracts (ECe) are often used. The standard shaking time is 0.5 hr for EC1:5 and standing time after soil saturation is 16 hrs for ECe. In this study, we investigated the effects of equilibrium time (shaking and standing time for EC1:5 and ECe, respectively) to test if the standard time is enough for precise and accurate measurement of EC. Two soils (silt loam and sandy loam) with seven levels of EC were prepared by adding salt solutions (1, 2, 4, 8, 12, 16, and 24 dS m-1) to the soils. The soils were used for experiments after 2-months aging. The EC1:5 was measured after shaking soil-water mixture for 0.5, 1, 2, and 3 hrs, and ECe was determined after standing the saturated soils for 4, 8, 16, 24, and 48 hrs. The results showed that 4 hrs of standing time for ECe are sufficient for most saline soils regardless of soil texture. However, occasional occurrence of large variations in ECe up to 25% indicates a necessity of longer (e.g., 24 hrs) standing time for some soils. Therefore, for long-term monitoring of ECe, it may be necessary to determine site-specific standing time for ECe. Unlike ECe, the variations in EC1:5 with shaking time was negligible. However, for soils treated with solution of high EC (24 dS m-1), the variability increased up to 6% variations. Therefore, it may be necessary to increase shaking time to 1 hr to ensure a precise measurement of EC1:5 particularly for high-saline soils. For precise measurement of EC by achieving equilibrium of ions, shaking for 1 hr is required for EC1:5 and standing for 24 hrs is appropriate for ECe.

An improved VOF-DEM model for soil-water interaction with particle size scaling

This study presents an improved VOF-DEM model where the Darcian velocity and a compound variable are treated as unknowns in the pressure-velocity calculation procedure such that the use of interpolated porosity at cell faces is minimised and stability is ensured even if the porosity field is not smooth or even ragged. A higher-order porosity estimation method is also used such that the porosity and interaction force are evaluated correctly when the CFD cell size is of the same order as the DEM particle size. Additionally, a particle size scaling technique is proposed to let the DEM particle size different from the real soil particle size and soil-water interaction forces are the same as when the real soil particle size is used. This is achieved by modifying the calculation of drag force. The solution scheme is verified in two case where analytical solutions exist. Particle size scaling technique is also used and tested in permeability tests and wave interaction with porous structure. Subsequently, the settling and collision of particles in water, dambreak of soil-water mixture and submerged landslides are simulated. With the present improvements and the particle size scaling, the capability of the VOF-DEM is extended in soil-water interaction problems.

Moisture alone is sufficient to impart strength but not weathering resistance to termite mound soil.

Soil is used for the construction of structures by many animals, at times admixed with endogenous secretions. These additives, along with soil components, are suggested to have a role in biocementation. However, the relative contribution of endogenous and exogenous materials to soil strength has not been adequately established. Termite mounds are earthen structures with exceptional strength and durability including weathering resistance to wind and rain. With in situ and laboratory-based experiments, we demonstrate that the fungus-farming termite Odontotermes obesus which builds soil nest mounds, when given a choice, prefers soil close to its liquid limit for construction. At this moisture content, the soil–water mixture alone even in the absence of termite handling undergoes self-weight consolidation and upon drying attains a monolithic, densely packed structure with compressive strength comparable to the in situ strength of the mound soil; however, the soil–water mixture alone has lower resistance to water erosion than the in situ mound samples, suggesting that termite secretions impart weathering resistance and thereby long-term stability to the mound. Therefore, weathering resistance and compressive strength are conferred by different aspects of termite soil manipulation. Our work provides novel insights into termite mound construction and strength correlates for earthen structures built by animals.

A hydrology-process based method for correlating debris flow density to rainfall parameters and its application on debris flow prediction

Antecedent effective rainfall (Ar) and rainfall intensity (I) play an important role in the formation process of debris flow. Establishing Ar-I threshold curve of debris flow is hence of great importance for early warning purpose. However, conventional statistical models require sufficient observation data, which is not feasible for developing countries without adequate field observation stations. To this end, a hydrology-process based method is proposed to construct the Ar-I threshold. In this model, debris flow is considered as a soil-water mixture composed of solid and water, the loose solid sources contributing to debris flow is provided by the rainfall-induced shallow landslide, and the water is from rainfall-induced runoff. A necessity of having the characteristics of debris flow is that the density of water-soil mixture should approximate to the density of debris flow ranging from 1.2 to 2.3 g/cm3. The value of 1.2 and 2.3 g/cm3, which represent lower and upper borders of the density of debris flow, is used as the threshold for predicting debris flow. The task of the model is to find out the rainfall parameters that correlate with the border value of density and use the searched data of rainfall parameters to fit corresponding curves. Verification of the proposed threshold was conducted based on field observation data of Jiangjia Gully located in Yunnan Province, China, which indicates the false negative and false positive rates of the threshold are 26.7% and 15%, respectively. The precision of the threshold is evaluated as 82.6% by the Receiver Operator Characteristics method, which can provide a solution for debris flow early warning.

Soil moisture influence in the soil tillage operations

This article presents results obtained by the author in an attempt to introduce new parameters that influence the working process of agricultural soil working machines, in the classical formulas that mathematically model the tillage draft force. This article naturally introduces soil moisture. To introduce soil moisture into the calculation formulas of the tillage draft force, other physical parameters affected by soil moisture were used: density, cohesion, adhesion, etc. In this article, is explicitly describes, only the variation of soil density with its moisture. Considering some phenomena such as soilswellingorshrinkage, required the development of an adequate mathematical model of the expression of the density of soil-water mixture, concerning the concentration of water and the densities of dry soil and water. The final formulas obtained are tested to experimental results from the literature. Finally, the author sets out his opinion regarding the use of the results in design calculations and regarding the elevation to the rank of physical law of a mathematical model represented by a formula with a large number of parameters, which in turn are still dependent on many others parameters.

Ultrasonic Dispersion of Nanocarbons in Soil-water Mixture

Nanocarbons (NCs) are a novel reinforcing material used to improve the mechanical properties of composite materials. As an application of this technology, research has been considering how nanocarbons can been used in soil reinforcement. However, to take advantage of the excellent reinforcing capabilities of nanocarbon tubes (CNTs) and nanocarbon fibers (CNFs), it is necessary to achieve a uniform distribution of nanocarbons in the composites. This paper presents a novel method for improving the dispersion of CNTs and CNFs in soil. The approach incorporates soil itself to stabilize the distribution of CNTs and CNFs. To examine the effectiveness of the method, specimens of soil with CNTs and CNFs were prepared with different concentrations of water. The specimens were then sonicated with ultrasonic equipment and imaged by field-emission scanning electron microscopy (FSEM) and transmission electron microscopy (TEM). The results showed that soil containing sufficient proportions of micro-particles (clay) can itself largely prevent the reagglomeration of NCs in the soil, thereby stabilizing their dispersion.

Estimation of settlement after soil liquefaction for structures built on shallow foundations

Soil liquefaction can occur when the strength and stiffness of soil are reduced by changes in the stress condition, and the settlement of structures can be affected by this phenomenon following an earthquake. To evaluate the liquefaction-induced settlement of structures, a simple equation that proposed the concept of equivalent viscosity of soil-water mixture is adopted. In this study, comprehensive finite element analyses are conducted and a viscosity chart is proposed that enables prediction of the liquefaction-induced settlement value. To accommodate different site conditions, several corrections are made based on experimental data obtained from literature; such corrections are found to be effective for proficiently estimating the liquefaction-induced settlement under differing conditions.

Solid–liquid coupled material point method for simulation of ground collapse with fluidization

An improved version of the solid–liquid coupled material point method (MPM) is proposed to simulate ground collapses with fluidization involving transition processes from soil structures to flowing mixture. A water-saturated soil is assumed based on porous media theory, and the physical quantities of the soil and water phases are assigned to two separate sets of particles (material points). The main contribution of this study is the introduction of the fractional step projection method for the time discretization of the momentum equation of the water phase on the assumption of incompressibility. Thanks to this, the proposed solid–liquid coupled MPM is capable of suppressing the pressure oscillations caused by the weak incompressibility of water, which is commonly assumed in the previous studies, and of representing the wide range of behavior of the soil–water mixture at relatively low computational cost. Also, B-spline basis functions are utilized for the spatial discretization to suppress the cell-crossing errors caused by particles crossing element (cell) boundaries. Several numerical tests are conducted to examine the performance of the proposed method that inherits the beneficial features of MPM and demonstrate the capability of reproducing a model experiment of wave collision to sandpile that exhibits the water flow-induced fluidization process of soil involving scouring, transportation and sedimentation.

Effects of extraction methods on soil water isotope and plant water source segmentation.

We used two types of soil with different physicochemical properties (loam and sand), oven-dried them, and then added the known isotopic composition mineral water that was reference water to compose the soil-water mixture with different soil water contents (loam: 0.15, 0.20, 0.30 g·g-1; sand: 0.10 g·g-1). After that, we set up different equilibrium time (loam: 3, 6, 12, 24, 48, 72, 96 h; sand: 96 h) to ensure that the dry soil particles were well mixed with the added water. The soil water was extracted by mechanical centrifugation and cryogenic vacuum extraction after equilibrium, and their isotope composition was analyzed. Results showed that the isotopic values of soil water extracted by mechanical centrifugation method had no significant difference in same water content with different equilibration times, but were more enriched compared with the reference water isotopic value. The maximum enrichment for hydrogen and oxygen isotope was 7.38‰ and 1.24‰, respectively. In contrast, cryogenic vacuum extraction method resulted in more depleted soil water isotopes than reference water, with the maximum depletion for hydrogen and oxygen isotope being 6.27‰ and 1.03‰, respectively. Moreover, the degree of depletion increased with the increases of equilibrium time (less than 24 h) at low water content, and became stable after 24 h. With the increases of soil water content, the isotopic composition of the extracted soil water was less affected by the two extraction methods. The water isotope value of loam that had high clay content, was more sensitive to the extraction method than the sandy soil that had low clay content. The difference of isotopic composition caused by extraction methods did not affect the plant water source segmentation.

ANALYSIS OF THE EFFECT OF INCIDENCE ANGLE AND MOISTURE CONTENT ON THE PENETRATION DEPTH OF L- AND S-BAND SAR SIGNALS INTO THE GROUND SURFACE

Abstract. We study the functional relationship between the dielectric constant of soil-water mixture and penetration depth of microwave signals into the ground at different frequency (L&S) band and incidence angles. Penetration depth of microwave signals into the ground depends on the incidence angle and wavelength of radar pulses and also on the soil properties such as moisture content and textural composition. It has been observed that the longer wavelengths have higher penetration in the soil but the penetration capability decreases with increasing dielectric behaviour of the soil. Moisture content in the soil can significantly increase its dielectric constant. Various empirical models have been proposed that evaluate the dielectric behaviour of soil-water mixture as a function of moisture content and texture of the soil. In this analysis we have used two such empirical models, the Dobson model and the Hallikainen model, to calculate the penetration depth at L- and C-band in soil and compared their results. We found that both of these models give different penetration depth and show different sensitivity towards the soil composition. Hallikainen model is more sensitive to soil composition as compared to Dobson model. Finally, we explore the penetration depth at different incidence angle for the proposed L- and S-band sensor of upcoming NASA-ISRO Synthetic Aperture Radar (NISAR) mission by using Hallikainen empirical model. We found that the soil penetration depth of SAR signals into the ground decreases with the increase in soil moisture content, incident angle and frequency.

Modeling groundwater flow and salinity evolution near TSF Żelazny Most. Part I – groundwater flow

Tailings which are by-product of the extraction of various metals (copper, gold, silver, molybdenum, etc.) are often stored in so called Tailings Storage Facilities (TSF), where they are deposited as a soil-water mixture by spigotting. In many cases the water discharged together with tailings to the TSF is rich in salts and other chemical compounds imposing negative pressure to the groundwater environment. Even in the case of total or partial lining of such facilities and well-developed drainage systems to control leaching, some portion of contaminated water often seeps either through the surrounding dams or the bed into adjacent groundwater bodies. Numerical models can be very helpful tools to assess the extent of the contamination and particularly to predict its potential development in the future. This paper and the companion one describe such a numerical model developed for Żelazny Most Tailings Storage Facility (south-west Poland), one of the world’s largest tailings sites. In the first part general information about the facility is provided and a 3D hydrogeological numerical model of the structure is described. Groundwater flow pattern near the facility obtained from numerical simulations is confronted with the measurements from a comprehensively developed monitoring system. Part II will be focused on the modelling of chloride transport in groundwater.

Experimental study on impact behavior of submarine landslides on undersea communication cables

Submarine landslides, which are characterized by large scale and long run-out distance, could destroy undersea communication cables, thus resulting in a great number of economic losses. In this work, an experimental apparatus is designed to simulate the relative motion between the submarine landslide and undersea communication cable, and investigate the impact behavior of a submarine landslide. The test results show that submarine landslide with larger thickness and larger particle size can generate larger impact force on the communication cables. With an increase of the sliding velocity, the evolution of the flow behavior and impact force of the soil-water mixture can be divided into three stages: 1) landslide stage, the mixture consists a water layer and a sand layer, the impact force increases with the sliding velocity and reaches a peak value at this stage; 2) transforming stage, sand particles start to be eroded by water, and result into a turbidity current layer above the soil-water interface. At this stage, the impact force decreases to a minimum value; 3) turbidity current stage, all of the sand particles are eroded by water, and the impact force increases again when increasing the velocity continuously.

KINETICS OF BIOLOGICAL TREATMENT OF PESTICIDE WASTEWATER

Pesticides are chemical substances intended to protect food crops and livestock from pests in order to promote agricultural productivity and protect public health. Contamination of soil, air and water and threat to human and animal health are the major constraints in the use of pesticides. Treatment of pesticide contaminated water is, therefore, paramount. Biological treatment provides the most economical option when compared with other treatment methods. The aim of the study was to develop a safe and effective farm biological treatment for low level agricultural pesticide wastewater. In this study, the degradation of the fungicide captan was evaluated under batch and continuous modes of operation with a retention time of 15 days. The results showed that the initial cell number (30.1 ´ 106 cells/mL) in the soil water mixture first declined with time during the first 24 hours reaching 15.6 ´ 106 and 11.1 ´ 106 cells/mL in the batch and continuous bioreactors, respectively. This was due to the inhibitory effect of pesticide on some of the soil microbial species that had less tolerance to captan at the initial concentration of 144 mg/L. Then, the microbial population started growing, reaching its maximum after 5 and 12 days in the batch and continuous bioreactors, respectively. The lag period and the specific growth rate for the batch bioreactor were 22 h and 0.096 h-1, respectively. A captan degradation efficiency of 89.6% was achieved after 10 days in the continuous bioreactor compared to a degradation efficiency of 100% after 5 days in the batch bioreactor. This study showed that the effluent from the continuous bioreactor had a captan concentration of 12 mg/L which is not acceptable for livestock drinking water. A half life of 52 h was observed in the batch bioreactor.

Bioaccessibility of PAHs and PAH derivatives in a fuel soot assessed by an in vitro digestive model with absorptive sink: Effects of aging the soot in a soil-water mixture

Aging soot in soil under neutral aqueous condition for 30days significantly (p<0.05) reduced the apparent gastrointestinal bioaccessibility (Bapp) of polycyclic aromatic hydrocarbons (PAHs) and PAH derivatives (d-PAHs) natively present in a composite fuel soot sample. Bapp was determined under fasting conditions by a previously developed in vitro digestive model that includes silicone sheet as a third phase absorptive sink in the small intestinal stage. Redistribution of contaminants from soot to soil, determined in independent experiments, was too small to affect Bapp. Prior uptake by soot of a commercial humic acid representing dissolved soil organic matter had no impact on Bapp. We identified two causes for the reduction in Bapp by soil and found they were approximately additive. One is an aging time-independent “matrix effect” attributable to competitive sorption by the soil of labile contaminant that is desorbed from the soot during the digestion test. The other is the dissolution of soluble substances from the soot during the aging process that increases soot surface area and nanoporosity. The increased surface area and nanoporosity drive contaminants from labile to nonlabile states in the soot and decrease the desorption into the digestive fluid, the former contributing most to the reduction in Bapp. The present study shows that mixing of raw soot with soil has important effects, both aging and non-aging, on the bioaccessibility of soot-borne contaminants.

Experimental study on the motion behavior and mechanism of submarine landslides

Submarine landslide is a common marine geo-hazard that shows different motion behavior with subaerial landslide. In this study, a test apparatus is developed to reproduce the extremely long distance movement of submarine landslides at different sliding velocities. The frontal behavior of subaqueous landslide under the dynamic pressure and shear stress of ambient water is described and analyzed. The evolution of the sediment concentration during the submarine landslide propagation is investigated. With an increase of the sliding velocity, the state of soil-water mixture can be divided into three stages: 1) landslide stage, the mixture consists a water layer and a sand layer; 2) transforming stage, a turbidity current layer appears above the sand-water interface, and the sand mass decreases gradually; 3) turbidity current stage, all of the sand particles are eroded by water and the sand layer disappears. In addition, the critical velocities between each stage are defined and investigated.