Soil-water Characteristic Curve Of Soil Research Articles

Slope Stability Evaluation of Reservoir Considering Soil-water Characteristic Curve of the Reinforced Ground Including Alginic Acid Sodium Salt

Alginic acid sodium salt is a type of biopolymer. It is a polysaccharide obtained from the most widely distributed brown algae among marine plants. Its main characteristics are nontoxicity and biodegradability. It is also considered a natural eco-friendly material because it is completely decomposed by microorganisms using only water and carbon dioxide. Moreover, sodium alginate aqueous solution mixed with water has high viscosity; hence, it is expected to effectively saturate and reinforce the soil. The soil-water characteristic curve shows the properties of the capillary pressure according to the water content of the soil. In other words, this curve can predict the shear strength of the soil. In this study, soil-water characteristic curves of soil reinforced with sodium alginate were studied. The stability of the reservoir slope reinforced with sodium alginate was evaluated using the input values of the numerical analysis, and the change in the shear strength of the soil was calculated. The results show that the increased concentration of sodium alginate solution increased the capillary pressure and residual water content of the soil-water characteristic curve, which increased the stability of the reservoir slope. The shear strength of the soil increased as the concentration and capillary pressure of the sodium alginate solution increased.

Framework to estimate the soil-water characteristic curve for soils with different void ratios

The soil-water characteristic curve (SWCC) contains information regarding the geometric pore space in a soil and is commonly used to estimate unsaturated soil properties, such as unsaturated hydraulic conductivity and unsaturated shear strength. Soil volume change can significantly affect the SWCC and the engineering properties of soil. Different SWCCs can be obtained if the soil specimens are prepared with different initial void ratios. The volumetric shrinkage curve (VSC) is commonly used to convert the SWCC in the form of gravimetric water content (w-SWCC) into a curve that is in the form of degree of saturation (S-SWCC). In this paper, a framework is developed in which different S-SWCCs are generated based on the measured w-SWCC of soil in a relatively loose condition and the VSC. The proposed framework is based on the concept of the pore size distribution function (PSDF). The estimated SWCCs corresponding to different initial void ratios from the proposed framework were verified by using experimental data from published studies.

Effects of organic content on soil-water characteristic curve and soil shrinkage

Organic matter commonly exists in the subsoil within tree rooting zones. The organic content of soil has been known to affect soil properties. In this study, soil organic contents at various locations around trees were found to be variable due to the ground flora and tree roots. The range of the soil organic content for the current study was between 0·9 and 12·5%. The objective of this study was to investigate the effects of the organic content on the shrinkage and soil-water characteristic curve of soil during rainy and dry seasons when the water content of the soil changes. Soil samples were collected from two locations on Singapore Island at depths of 0·1 and 0·3 m. A centrifuge was used to measure the water content of the specimens at suctions up to 250 kPa, and chilled-mirror psychrometry was used for higher suction. Shrinkage tests were also conducted. The results show that a higher organic content was associated with a greater shrinkage rate and a higher suction corresponding to the residual water content. For finer soils, a higher organic content comes with a lower air-entry value.

Evaluation of Bouwer-Rice Large-Particle Correction Procedure for Soil Water Characteristic Curves

Abstract The Bouwer-Rice correction method to account for large particles excluded during laboratory testing to measure the soil water characteristic curve (SWCC) was evaluated on samples of well-graded alluvium. A large-scale hanging column apparatus was used so that tests could be conducted on specimens containing all particle sizes. The analyses show that SWCCs measured on the fraction of alluvium finer than the No. 4 U.S. sieve (4.8 mm) can be corrected reliably to represent the SWCC of bulk soil or fractions of bulk soil corresponding to different large-particle thresholds. The method can also be used reliably to correct SWCCs measured on soils prepared with different large-particle thresholds (e.g., finer than 25 mm, 12.5 mm, or 4.8 mm). Dry density of the finer fraction being tested must be carefully controlled to match the dry density of the finer fraction in the soils containing large particles. An equation is described for computing the dry density of the finer fraction in a bulk soil. A simplified version of the Bouwer-Rice method is also proposed and evaluated. In this method, a SWCC test is conducted on the finer soil fraction with dry density matching that anticipated in the field, the van Genuchten equation is fit to the measured SWCC to define the shape parameters α and n, and then the SWCC for the field application is computed using the fitted α and n from the test on the finer fraction, saturated volumetric water content of the bulk soil in the field, and a residual water content of zero. Analyses show that this modified Bouwer-Rice method is simpler and results in an accurate representation of the SWCC of soil containing large particles.

Soil water content, suction and characteristic curves in the coastal watersheds of the Pearl River Delta

The underlying bedrocks of Zhongshan and Zhuhai in the Pearl River Delta are mainly granite.Weathered granite soils in this region contain large proportions of gravel and grit,giving the soils a peculiar soil water characteristic curve (SWCC).This literature focused on the coastal watershed of Zhuhai City and analyzed soil texture in the watershed using "Mastersizer 2000".The soils in the watershed are mainly sandy loam and loamy sand.On this basis,changes in the characteristics of the soil water content,suction,along with the responses to precipitation and evapotranspiration were analyzed.A scatter plot of the soil water content versus soil suction illustrates that SWCC (including absorption and desorption processes) at all depths of the experimental plot follows an L-shaped curve.For the desorption process,SWCC for soils with larger proportions of fine particles shows an inverse S-shaped curve for low water content and high suction sections.In order to obtain desired effects,we propose the use of "Gauss" and "Dose-response (Bi-dose response)" curves to fit SWCC.

Evaluation of Various Pedo-Transfer Functions for Developing Soil-Water Characteristic Curve of a Silty Soil

Abstract This paper describes development of the soil-water characteristic curve (SWCC) of a silty soil by measuring its matric suction _m, corresponding to different gravimetric water contents w. To achieve this, a field tensiometer and a dew point potentiameter (WP4) were employed. For this soil, the SWCC was determined indirectly using the estimation algorithms known as pedo-transfer functions (PTFs), which are based on volume-mass properties and the grain-size distribution characteristics, and are available in a commercial database SoilVision. In addition to this, experimental results were used for developing the SWCC of the soil, using various fitting functions cited in the literature and available in the database. An attempt has been made in this technical note to demonstrate the usefulness of these three methods for obtaining the SWCC of the silty soil. The study reveals that the PTFs developed previously to estimate SWCCs match very well with the experimental results.

Predicting Bimodal Soil–Water Characteristic Curves

Failure of colluvial soil deposits induced by rainfall is a common geohazard in the natural terrain. Many colluvial soils are widely and gap graded with a minimal sand fraction. In order to study the pore water pressures in such gap-graded, unsaturated soil deposits through a seepage analysis and to evaluate the stability of these soil deposits, the soil-water characteristic curves for gap-graded soils must be known. Usually, gap-graded soils exhibit bimodal grain-size and pore-size distributions. This technical note presents a theoretical continuum method for the determination of soil-water characteristic curves for soils with a bimodal or multimodal pore-size distribution. Based on the capillary law, the water content in a multimodal soil is equal to the sum of water stored in each pore series in the soil. Therefore, the bimodal or multimodal soil-water characteristic curves can be obtained by combining the unimodal soil-water characteristic curves for all components of the soil corresponding to the pore series weighted by the respective volumetric percentages. The proposed method is verified using experimental soil-water characteristics data of sand-diatomaceous earth mixtures with dual porosity.

Experimental investigations of the soil-water characteristics of a volcanic soil

Rain-induced landslides are common around the world. To analyse transient seepage and to predict pore-water pressure distribution in unsaturated slopes subjected to rainfall infiltration, it is essential to study soil-water characteristics and water permeability functions. The soil-water characteristic curve (SWCC) is a relationship between suction and water content or degree of saturation. Conventionally, only the drying soil-water characteristic curve of soil specimens is determined in a pressure-plate extractor without the application of any external stress. In this paper, the influences of initial dry density and initial water content, history of drying and wetting, soil structure, and the stress state upon the desorption and adsorption soil-water characteristics of a completely decomposed volcanic soil in Hong Kong are examined and discussed. The experimental results presented are obtained by using a conventional volumetric pressure-plate extractor and a newly modified one-dimensional stress-controllable pressure-plate extractor with deformation measurements. The SWCC of a recompacted specimen is very different from that of a natural specimen with the same initial soil density and initial water content. The SWCC of the recompacted specimen is highly dependent on the history of drying and wetting. The rates of desorption and adsorption are substantially higher at the first drying and wetting cycle than at the second drying and wetting cycle. The size of the hysteresis loop of the recompacted specimen is considerably larger than that of the natural specimens. The SWCC of soil is stress-state dependent. For recompacted specimens subjected to different stress states, the higher the applied stresses, the lower the rate of desorption and the smaller the size of the hysteresis loops. However, for natural specimens, the size of the hysteresis loops seems to be independent of the stress state. Under a higher applied stress, natural specimens exhibit lower rates of desorption and adsorption.Key words: volcanic soil, SWCC, drying and wetting, stress-state dependent.