Water Content Of Soil Samples Research Articles

HYGROSCOPIC WATER CONTENT AS AN INDICATOR OF SOIL DISPERSITY:THERMODYNAMIC BASIS AND EXPERIMENTAL VERIFICATION

The adsorption properties of dispersed systems are determined by their surface energy, therefore the indicators of hygroscopy (adsorbed water content) and dispersity (specific surface area of the solid phase) of soils and sediments are in close mutual correlation. This well-known empirical fact received a new fundamental interpretation based on the theory of disjoining water pressure according to Deryagin in the form of a thermodynamic equation connecting the specific surface area, hygroscopic water content of soil samples and the relative humidity of the air in the laboratory room. The theoretical equation allowed us to substantiate the methodology for quantifying the hydrophilic specific surface area of soil samples based on widespread data on their hygroscopy. A comparison of the new method with the standard BET-analysis of the specific surface area, as well as with the previously proposed physically based method for its determining by the slope of thermodynamic water retention curves, showed their statistically reliable agreement in a wide range of estimated specific surface area values from 5 to 340 m2×g-1 for soil samples of different genesis and texture.

Experimental Study on Influencing Factors of Soil Complex Resistivity

Complex resistivity is one of the important parameters in electrical prospecting. The application of complex resistivity in oil and gas resource evaluation, engineering investigation and contaminated site evaluation can avoid the influence of low contrast on detection accuracy, and has a good application prospect. In order to improve the study of the influence of soil physical properties on complex resistivity and promote the wider engineering application of complex resistivity exploration. In this paper, the effects of dry density and water content on complex resistivity were studied by laboratory tests, and the following laws were obtained: under the same frequency, the lower the water content of soil sample, the higher the resistivity; The higher the degree of compaction, the lower the resistivity.

Effect of geotextiles with different masses per unit area on water loss and cracking under bottom water loss soil conditions

Soil water loss is an important component of the water balance in irrigated agriculture. This study investigated the effects of geotextiles on water loss during soil drying and cracking. The results indicate that the residual water content of soil samples increased by 98.5%, 145.5%, and 164.7% with geotextile masses per unit area of 100, 300, and 400 g/m2, compared that of soil without geotextiles. There are two water loss stages of soil, the "rapid loss" and the "residual loss,” under the condition of bottom water loss, which is different from the evaporation stage of normal soil without bottom water loss. When a geotextile is added to the soil, the stages of bottom water loss will become "rapid loss, deceleration loss, and residual loss." When the mass per unit area of 400 g/m2 geotextile was used, the crack ratio, probability entropy, and fractal dimensions decreased by 15.19%, 6.47%, and 5.81%, respectively. The geotextile mass per unit area increased the specific surface area of the soil, and water retention was improved. When the mass per unit area of the geotextile increased, the interface friction between the soil and geotextile increased, and the cracking of the soil was effectively inhibited.

Effects of pre-dynamic loading on hydraulic properties and microstructure of undisturbed loess

The frequent earthquakes in the loess area and the geological disasters induced by them have caused huge threats to the safety and property of the local residents, and most disasters are highly dependent on moisture in the soils. In this study, the effects of pre-dynamic loading on the hydraulic properties of loess are investigated through the variation of soil water characteristic curves, which control the interaction between soil and moisture. The results are analyzed based on the combination of mercury intrusion porosimetry (MIP) and scanning electron microscope (SEM) tests, which reveal the influence of pre-dynamic loads on microstructure, for a more comprehensive understanding. It is found that both the initial water content of soil samples and the magnitude of applied pre-dynamic loads have impacts on soil water characteristic curve (SWCC). When initial moisture content is low, the dynamic load causes the loess structure to form a seismic damage zone, resulting in downward movement of SWCC and a reduction in the air entry value. When the moisture content is high, the soil structure gets denser after vibration, leading to reversed influence. For both cases, the effect increases as the PGA amplitude increases. The outcomes of different experiments have achieved good agreement.

Experimental study on the effect and influence mechanism of boundary hydraulic pressure on frost heaving

Water supply is one of the dominant factors determining the frost heave, and many researchers have studied the occurrence of frost heaving under the water boundary conditions of no-water supply or no-pressure water supply. Soil freezing is fed by confined groundwater in some cases, however, limited studies have focused on the role of boundary hydraulic pressure. To clarify the effect of boundary hydraulic pressure on soil frost heaving, a series of one-directional soil freezing experiments under various boundary hydraulic pressures were conducted, and the freezing characteristics, pore water pressure (PWP), hydraulic conductivity and the microstructure of unfrozen soil in the longitudinal section were observed and analyzed. The results showed that boundary hydraulic pressure not only increases the frost heave but also inhibits the freezing front from advancing. The increase in boundary hydraulic pressure favors the development of micro-lenticular cryostructure and layered cryostructure. Moreover, the total water intake volume and moisture content after tests increase with increasing boundary hydraulic pressure. The increased water content of soil sample and the PWP gradient of frozen fringe account for the increased frost heave. In addition, the results demonstrated that the hydraulic pressure can enhance the permeability of unfrozen zone and frozen fringe. Microscopic analysis showed that hydraulic pressure can promote the pore orientation of longitudinal section of the soil, which transfers from the uniform distribution to the triangular distribution.

Parameterization of the Model of Artificial Clay Freezing Considering the Effect of Pore Water Salinity

This paper considers the artificial freezing of an argillite-like clay layer containing a NaCl salt solution in its pore space. The experimental results of the thermophysical properties of the clay with various salinities and water content in soil samples are presented. We determine the parameters of the soil freezing characteristic curves, the dependences of the specific heat capacity, and thermal conductivity based on temperature and salinity. These parameters are used in the formulation of a simple thermodynamic model for the artificial freezing of a clay layer with a single freezing pipe. The model includes diffusive transfer of heat and salt concentration, as well as salt precipitation when the eutectic point is reached. The motivation for using the simplified model is to understand the general patterns of soil freezing when considering the effect of salinity, as well as to test the proposed numerical finite-difference algorithm for solving the problem of freezing a clay layer based on the method of equivalent heat capacities. Using the algorithm, we analyzed the regularities of the redistribution of dissolved and precipitated salt in frozen soil, and also evaluated the effect of diffusive salt transfer on the numerical solution.

Effect of Oil Pollution on Permeability of the Grey Desert Soil under Freeze-thaw Cycles in Arid Areas of Western China

ABSTRACT There are abundant oil resources in Xinjiang, and the exploitation of oil resources could easily pollute the soil. In this paper, the impact of oil pollution on permeability of the gray desert soil affected by freeze-thaw cycles under a dry and cold climate of Karamay region in Xinjiang was studied. First, varying-head infiltration tests were conducted on soil samples with different water contents and pollution intensity without exposing to freeze-thaw cycles. The variability of permeability were analyzed employing the scanning results of the polluted soil samples by an electron microscope. Then several freezing and thawing cycle tests were implemented on the samples. The test results shown that the soil permeability was optiomal and the permeability coefficient was highest when the crude oil pollution intensity was 0.61% and the water content was 15.53%. With the water content in soil samples being the same, the soil permeability coefficient increased in the beginning and then decreased as the pollution intensity increased. When the pollution intensity ranging from 0.5% to 1.75%, the freezing and thawing condition could be the leading factor affecting the soil permeability. However, when the oil content was within the range of 1.81% – 2.41%, the freezing and thawing condition could not be the leading factor affecting the soil permeability. The results provided in this study could serve as a relevant basis for the remediation of soil pollution in oil production plants in arid areas of Western China.

Role of biochar from corn straw in influencing crack propagation and evaporation in sodic soils

Soil degradation has become one of the serious global environmental problems, biochar is a recyclable natural material which has been widely used in soil remediation. Soil cracking can significantly change the migration path of water and nutrients in the soil, which affects the remediation performance of biochar and plant growth. The effects of different amounts of corn straw biochar on the evaporation and drying shrinkage characteristics of sodic soil are investigated in this paper. Different amounts (by mass) of biochar: 0%, 1%, 2%, 4% and 8% are added to the soil. A customized experimental device is used to measure the rate of evaporation of water and record the images of surface crack development of the samples during drying. Using image processing technology, the crack rate, crack entropy and fractal dimension of the cracks are obtained. The experimental results show that: (1) biochar can change the drying and cracking characteristics of sodic soil by changing the evaporation process of the soil. With biochar contents of 1%, 2%, and 4%, the residual water contents of soil samples are decreased by 4.83%, 43.94% and 85.71%, respectively. With an 8% biochar content, the residual water content of soil sample is increased by 64.49%, (2) the addition of biochar reduces the rate of cracking and fractal dimension of sodic soil. With an 8% biochar content, the rate of cracking and fracture fractal dimension are reduced by 46.39% and 13.74%, respectively, (3) the addition of biochar can effectively reduce the degree of the disorderly arrangement of surface cracks. At biochar contents of 2%, 4% and 8%, the crack entropies are decreased by 2.22%, 6.46% and 7.37%, respectively, and (4) the mechanisms in which biochar changes crack development in sodic soil are: (a) improving the soil texture and reducing the bulk density of soil and (b) increasing the number of water migration channels, soil aggregates and the water retention capacity in the soil.

Experimental Study on Dynamic Properties of Nano-MgO-Modified Silty Clay

To study the dynamic properties of nano-MgO-modified soil, the contents of nano-MgO which were 0%, 1%, 2%, 3%, 4% and 5% of the dry weight for soil were added into the soil. The water content of soil samples were 16% and 22%. The variation of shear modulus and damping ratio of soil was analyzed through the resonant-column test of the modified soil. The results show that with the increasing of shear strain, the shear modulus of soil decreases and the damping ratio of soil increases, the shear modulus for nano-MgO-modified soil reaches the maximum when the content of nano-MgO is 5%. The maximum shear modulus of soil with water content of 22% is smaller than that of soil with water content 16% under the same confining pressure, the shear modulus of soil increases linearly with the increasing of nano-MgO content. The reinforcement mechanism of the nano-MgO-modified soil was analyzed such as pore filling effect of nano-MgO, effect of water content, effect of vibration compaction, interaction between a nano-MgO group and a soil particle, interaction between several nano-MgO groups and soil particles.

Study on Frost Heaving Evaluation of Typical Soil Samples along Qinghai-Tibet Highway

Based on the geological survey data of 167 boreholes along the Qinghai-Tibet Highway, the relationship between frost heaving force and natural density and water content of soil samples was analyzed and evaluated. The results show that the natural density along the line is concentrated from 1.9 g·cm−3 to 2.2 g·cm−3. The frost heaving force decreases with the increase of the natural density. Frost heaving force is affected by natural density in three stages. The frost heaving force increases with the increase of natural water content, which can be divided into three stages, too. The surface water system is developed and the water content in the shallow layer is relatively large, which makes the frost heaving force reach 37kPa, which is the maximum along the line.

Influence of plasticity on unfrozen water content of frozen soils as determined by nuclear magnetic resonance

The mechanical properties of frozen soils are closely related to the unfrozen water content. It has been generally recognized that the unfrozen water content varies with plasticity of soils, while the quantitative relationship between the plastic index and the unfrozen water content is yet to be further examined. This paper takes soil samples with different plasticity as study objects, which are prepared from two typical soil materials, i.e., the Chinese ISO standard sand and bentonite. Nuclear magnetic resonance (NMR) is used to measure the unfrozen water content of soil samples under different temperatures. Test results show that there are three stages in the soil-freezing characteristic curve (SFCC), i.e., the super-cooling stage, the rapid-drop stage and the stable stage. With the increase of the plasticity index, the super-cooling stage is less significant, while the curve in the rapid-drop stage becomes gentler. In the stable stage, the unfrozen water content is barely affected by plasticity. A piecewise function consisting of a linear formula and a power formula is then proposed to describe the SFCC, where the formula parameters are functions of the plastic index. It is found that the unfrozen water content calculated by the proposed formula agrees with the measured results.

Effects of temperature, dry density and water content on the thermal conductivity of Genhe silty clay

As an important parameter to consider the thermal stability of road engineering in cold regions, thermal conductivity is largely affected by temperature, water content, dry density, and etc.. When investigating thermal conductivity, setting the dry densities and water contents of soil samples according to compaction curve agrees better with actual engineering conditions because of its compaction characteristic for subgrade soil. Therefore, experiments on thermal conductivity of 9 groups of soil samples corresponding to different water contents at the compaction curve were carried out under −40 ℃~20 ℃. It was found that thermal conductivity decreases linearly with the decrease of temperature in positive temperature range and increases exponentially in negative temperature range, which is closely connected to the variations of thermal conductivity, contents and interactions of every phase with temperature. Multiple linear regression analysis showed that water content has a slightly higher effect on thermal conductivity at positive temperature than that of dry density; however, its effect is about twice of that of dry density at negative temperature. Then, an assessment method combining Root Mean Square Error (RMSE) and Root Mean Square Value (Xrms) was proposed to evaluate the predictive capabilities of two classical models (Johansen’s model and the CK model) effectively.

Development of a FBG water content sensor adopting FDM method and its application in field drying-wetting monitoring test

Fused deposition modelling (FDM) has been widely used in the field of sensor production, however, sensor fabricated adopting FDM in monitoring water pressure is seldomly discussed. In this study, one Fiber Bragg Grating (FBG) water content sensor has been designed and fabricated in order to monitor the variation of water pressure at the field. It’s worth noting that the advanced material, Polylactic Acid (PLA), has been used in fabricating sensor with favorable stability. After the fabrication of FBG sensor, calibration test was conducted by controlling and measuring water content of soil sample in a sealed chamber through manipulating pressure volume controller. It has been validated that this pressure sensor adopting FDM fabrication process has quick response and high sensitivity. Afterwards, field application of this type of sensors have been used in measuring the variation of soil water content continuously, while reading from different depth of this sensor can be compared and analyzed to summarize the influence of nature rainfall condition about the ground. To validate and verify the reliability and authenticity of developed FBG sensors, the conventional sensors have been implanted at the same depth of FBG sensors and comparison have been conducted in the entire monitoring period. It has been verified that FBG sensors have good performance when embedded into the melted PLA material, while its application in measuring soil water pressure is more sensitive and accurate.

Development of pot-cover effect apparatus with freezing-thawing cycles

‘Pot-cover effect’ refers to the phenomenon of moisture accumulation beneath the pavement under condensation or desublimation because the vapor transfer in the soil is blocked by the pavement. To study this phenomenon in the laboratory, we have developed the pot-cover effect apparatus with freezing-thawing cycles (PEAFC), which consists of three parts, namely, the vapor transfer system, the temperature control system, and the temperature and water content monitoring system. The major functions of this apparatus include: simulation of both vapor transfer and freezing-thawing cycling in the soil, real-time monitoring of the temperature and the water content in soil samples, and one-dimensional heat and moisture transfer in the samples. The FDR (frequency domain reflectometry) sensors of the apparatus are calibrated and a calibration formula is proposed to eliminate the water content measurement errors induced by temperature changes. Constant temperature difference tests and a freezing-thawing cycling test are conducted with the apparatus. Results indicate that the apparatus can control the water replenishment in the soil samples, monitor the vapor transfer in the samples in real time, and simulate the vapor transfer process under the condition of the freezing-thawing cycling in the soil. These tests verify the effectiveness and reliability of the apparatus, which indicates that the development purpose is achieved.

A laboratory study on pull-out resistance of geogrid in clay soil

Geosynthetics such as geotextiles, geogrids and geocells are outstanding materials for reinforcement of soils. Recently, reinforcing the clay soils with geosynthetics, by increasing the bearing capacity and decreasing over consolidation, was used increasingly in geotechnical applications. The behavior of soil with reinforced material is crucial on design of reinforced soil. In this study the interaction between geogrid and clay soil was investigated by pulling out the geogrid experimentally with the help of direct shear tests machine. In experiments the geogrid was placed on shear surface that was the midpoint of test mold. The soil samples were prepared with different water content that was including optimum water content (OWC). A special cap was designed to pull-out the reinforcing material through the soil sample. According to experimental results, the variation of pullout load against displacement seems to be similar to classical load-displacement behavior of soil and it increases when the normal stress increases. Under the same normal stresses, pull-out load observed to be greater when the soil sample has OWC. At stress level σ = 27,2 kPa, when water contents of soil samples increase 60%, the pull-out loads increase approximately 30%. These observations can be interpreted the interlocking between soil and geogrid is stronger if the water content of soil samples are equal to OWC. It is also showed from the tests results that pull-out load values are generally greater than interfacial strength of soil samples.

Effect of cement additives on unconfined compressive strength of warm and ice-rich frozen soil

The effect of nine cement additives on the unconfined compressive strength (UCS) of warm and ice-rich frozen soils was analyzed. After 7days of curing at −1°C, the UCS at −1°C, the freezing-point depression and changes in the water content of soil samples were measured to explore the additive effect and mechanism. The optimum additive dosage was determined to improve engineering applications. The conclusions were: (1) attapulgite, metakaolin, nano-silicon dioxide (SiO2), silica fume and hardener accelerator increased the UCS by reducing the water content of frozen soils; (2) sodium hydroxide (NaOH), sodium silicate (Na2SiO3) and sodium lignosulfonate thawed the ice and reduced the UCS of frozen soil samples; (3) when frozen soil with a water content of 30% and 90% was mixed with 15% cement, the optimum dosages were 2% and 8% metakaolin and 0.49% and 0.62% hardening accelerator, respectively.

Quantification of soil water retention parameters using multi-section TDR-waveform analysis

Soil water retention parameters are important for describing flow in variably saturated soils. TDR is one of the standard methods used for determining water content in soil samples. In this study, we present an approach to estimate water retention parameters of a sample which is initially saturated and subjected to an incremental decrease in boundary head causing it to drain in a multi-step fashion. TDR waveforms are measured along the height of the sample at assumed different hydrostatic conditions at daily interval. The cumulative discharge outflow drained from the sample is also recorded. The saturated water content is obtained using volumetric analysis after the final step involved in multi-step drainage. The equation obtained by coupling the unsaturated parametric function and the apparent dielectric permittivity is fitted to a TDR wave propagation forward model. The unsaturated parametric function is used to spatially interpolate the water contents along TDR probe. The cumulative discharge outflow data is fitted with cumulative discharge estimated using the unsaturated parametric function. The weight of water inside the sample estimated at the first and final boundary head in multi-step drainage is fitted with the corresponding weights calculated using unsaturated parametric function. A Bayesian optimization scheme is used to obtain optimized water retention parameters for these different objective functions. This approach can be used for samples with long heights and is especially suitable for characterizing sands with a uniform particle size distribution at low capillary heads.

Near-Infrared-Spectroscopy for Determination of Carbon and Nitrogen in Indian Soils

ABSTRACTThe present study aims to evaluate the potential of near-infrared reflectance (NIR) spectroscopy to determine the carbon and nitrogen content in soils and also to assess the effectiveness of NIR spectroscopy to predict carbon and nitrogen content in freshly collected soil samples. Soil samples (n = 179) were collected from different locations in India. Soil carbon and nitrogen contents were successfully predicted (R2 = 0.90 for carbon and R2 = 0.85 for nitrogen) by NIR spectroscopy. The root mean square error (RMSE) and ratio performance deviation (RPD) for the validation of predicted equations for carbon and nitrogen were 0.83 and 2.83 and 0.01 and 6.98, respectively. The efficacy of NIR spectroscopy on the prediction of carbon and nitrogen content in Indian soils is highly reliable. Water content in soil samples could affect the NIR absorbance spectra and in turn affect the quantification of carbon and nitrogen.

A New Approach for Determination of Volumetric Water Content in Soil Samples by Gamma-Ray Transmission

A new method was presented for the purpose of volumetric water content determination in any soil sample by gamma-ray transmission. Monte Carlo (MC) simulation technique was used to determine the functional behavior of the linear attenuation coefficient of soil samples having different water contents for three soil samples. Using this functional behavior, the linear attenuation coefficients of dry soil and water were obtained from the intercept and the slope, respectively. It was experimentally shown that the mass attenuation coefficients of soil samples were not sensitive to the chemical composition but only to the physical density. This independence was exploited in this study to obtain the linear attenuation coefficient of a completely dry soil which was found to be 0.1409, 0.1274, and 0.1657 cm−1 for Gumushane, Ardahan, and Trabzon soil, respectively. The linear attenuation coefficient of water was determined to be 0.09 cm−1. Then, the volumetric water contents were obtained by measuring the gamma-ray intensities passed through three wet soil samples. The results were found to be 0.186, 0.182, and 0.214 cm3 cm−3 for Gumushane, Ardahan, and Trabzon soil, respectively. The results obtained by the method introduced were compared with the results obtained using gravimetric method. A very good agreement was observed.

Progress of Numerical Simulation for the Salinization of Soil Caused by the Discharge of Salt Containing Waste Water

The pollution caused by oil extraction waste water to the environment has gradually caused the attention of environmentalists; high salinity oil extraction wastewater will also cause soil salinization and bring great harm to the environment. However, due to the lack of the standard data and instructional experiment methods, the environmental protection department can’t set up formal system of desalination processing. In this paper we give the mathematical model for the simulation of the salinization process caused by the discharge of salt-containing waste water, and explain the application of Hydrus-1D for simulating water and salt in the soil on the basis of experiment data. The water content of soil samples is measured through soil-column experiment and salt content is simulated with Hydrus-1D according to the experiment results and model parameters and the composition of the bottoms of soil immersed in the salt solution. The application of Hydrus-1D for simulating water and salt in the soil determines the boundary condition and initial condition of the simulation, and the model parameters are corrected based on the experimental data of water content and salt content in the thirtieth day. The basic soil water movement equation are Richards equation and van Genuchten-Mualem model, and the basic soil movement equation is advection-dispersion equation for simulating; upper boundary condition is atmospheric boundary, lower boundary is a constant flux boundary, i.e., the initial water content, the initial salt content. The model parameters have adaptability and representative for simulating water and salt in the soil.