A Retention Curve Prediction for Unsaturated Clay Soils (original) (raw)
Related papers
E3S Web of Conferences
The design of engineering structures is still a challenging task when considering unsaturated soil mechanics behaviour. The present paper focuses on analysing Soil Water Retention Curves (SWRC) for clayey soil samples collected from a purpose built experimental embankment. SWRC determination is crucial when analysing geotechnical parameters of the soil. During the measurements, soil samples were subjected to wetting and drying cycles using a stage procedure (where the process is carried out in stages to allow equalisation) and continuous processes. The methods used for obtaining the suction curves were high suction tensiometer, attached at the bottom of the sample, and pressure plates with suctions applied up to 800 kPa. The study compares laboratory methods on measuring suction for sandy clay samples. It proves that the wetting and drying history have an impact on the hydraulic behaviour of tested material. In order to give a wider picture of soil behaviour it also presents the outputs as a function of matric suction and volumetric and gravimetric water content, and degree of saturation.
Comparison of Water Retention Curves for Clayey Soils Using Different Measurement Techniques
2006
Soil water retention curves were determined using four different techniques for suction measurement. Transistor psychrometer and non‐contact filter paper techniques were used for total suction determinations; pressure plates and in‐contact filter paper techniques were used for matric suction measurements. The soil water retention curves (WRC) were determined for bentonite, speswhite kaolin and a mixture of kaolin and sand (70 percent: 30 percent by mass). Specimens were prepared at their liquid limits and the WRC were ...
Laboratory Method for Estimating Water Retention Properties of Unsaturated Soil
Walailak Journal of Science and Technology (WJST), 2012
Soil hydraulic properties are necessary for modeling water flow and solute transport in the vadose zone. However, direct measurement of these characteristics in field conditions is tedious, time-consuming and expensive. In this study, a laboratory method was used to characterize soil water retention curves of three soil samples in the region of Bouhajla (Central Tunisia). For experimental purposes, volumetric water content and pressure head values were measured using the gravimetric method and Watermark sensor, of a small disturbed soil core, respectively, during a drying cycle under the effect of evaporation. The van Genuchten model was fitted to the measured retention curves with the RETC software to determine residual water content (θ r), saturated water content (θ s) and the two shape parameters; α and n. Strong correlations were found between the fitted and measured retention curves. The van Genuchten model was also fitted to the retention curves measured by pressure chamber (as the reference method). The results were evaluated by calculating the root mean square error (RMSE) and the geometric mean error ratio (GMER). Statistical analysis proved the success of the proposed method for estimating van Genuchten soil retention parameters of the studied soils. A Mann-Whitney test performed at the significance level of 0.05 showed no significant difference between the two methods.
Water retention in unsaturated soils subjected to wetting and drying cycles
2011
The suction is an essential parameter to describe and understand the behavior of unsaturated soils. The ability of unsaturated soils to retain water is quantified by determining the water retention curves (WRC), which express the hydraulic behavior of porous materials such as soil. These curves are determined by subjecting samples to several drying and wetting cycles. The curve during drying path is located above the wetting curve, developing a hysteresis phenomenon [1], and value of content water at a given suction value depends on the path used to reach this point. The aim of this paper is to present a study on the hydraulic behavior of soil, water retention capacity due to drying and wetting cycles, pointing out the hydro-mechanical behavior of unsaturated soils. In the first part, the effect of physical and mechanical properties of soil [32] (initial void ratio, particle size, cohesion, density...) on the water retention is presented. In the second part, a complete numerical model was developed, based on the empirical model of Van Genuchten [18], to model the two boundary curves, and the experimental scanning data were bestfitted using the same theory of Mualem model [13]. This complete model requires 4 parameters.
International Journal of Geosciences, 2019
Accurate evaluation of unsaturated soil properties is critical for the design of geotechnical and geo-environmental structures such as road pavements, foundations, and earth dams. Water retention activity in soils which is used to predict the stability or seepage problems in the ground is one of the key features in unsaturated soil mechanics. Thus, many experimental works have reported on the unsaturated soil properties, and the soil-water characteristic curve (SWCC) test has contributed significantly to the interpretation of matric suction. Since traditional instruments cannot apply stress in SWCC tests, some researchers have developed suction controlled triaxial apparatus, by which SWCC tests are performed under different stress states. Determination of SWCCs under stress conditions similar to those in the field is key for interpretation of the hydro-mechanical behavior of unsaturated soils. This study conducted SWCC tests of unsaturated silt soil in low matric suction ranges under both drying and wetting conditions. The SWCCs were measured under one-dimensional and isotropic confining stresses ranging from 50 to 450 kPa. The micro porous membrane method was used instead of high air entry ceramic disk for controlling relatively low matric suction. The range of matric suction controlled was from 0 to 20 kPa. The study revealed that the measured SWCC in low matric suction ranges seems to be affected by the influence of stress conditions. Isotropic confining stress caused the void structure of the specimen to become dense and consequently, soil moisture flow movement also decreased. The water retention activity was obviously high, and the point regard to air entry value was larger. The study further suggests that the current methods adopted for estimating unsaturated soil properties require further development to take into account the effect of different stress conditions. How to cite this paper: Habasimbi, P. and Nishimura, T.
Effect of clay minerals on the suction stress of unsaturated soils
Engineering Geology, 2020
The primary objective of this study is to investigate the characteristics of suction stress in two types of unsaturated weathered soils with different clay minerals. To obtain the mineralogical properties of the two samples, X-ray diffraction and scanning electron microscope analyses were conducted, and a large amount of kaolinite and montmorillonite was subsequently contained in the granite soil and mudstone soil, respectively. The granite soil was first remolded to obtain the same relative density and particle size distribution as the mudstone soil, and an automated soil-water characteristic curve (SWCC) apparatus was used to measure the water content and matric suction. The weathered granite soil had a higher air-entry value, and the volumetric water content was significantly changed by small changes in matric suction. The weathered mudstone soil showed a large hysteresis in the SWCCs between drying and wetting processes because of the ink-bottle effect, contact angle effect, and trapped air. The suction stress characteristic curve (SSCC) demonstrates that weathered mudstone soil had a larger magnitude of suction stress. The SSCCs of the weathered granite and mudstone soils display similar tendencies to the SSCCs of silt and clay, respectively. Therefore, the unsaturated characteristics considerably depend on the clay mineral composition and particle size distribution.
Soil Water Characteristic Curves of Compacted Marine Clay
The Journal of solid waste technology and management, 2021
The soil water characteristic curve (SWCC), also known as soil water retention curve (SWRC), describes the relationship between water content and soil suction in unsaturated soils. The importance of SWCC can be seen, as the relationship affects geotechnical properties such as shear strength, volume change, permeability and deformability of unsaturated soils. This paper presented a preliminary study on the effect of initial water content and the density on SWCC on unsaturated compacted kaolin. Filter paper technique was used for suction measurement on the unsaturated compacted kaolin soil. Filter paper was used to determine total suction and matric suction through contact and noncontact technique. The calibration curve was used to relate with the gravimetric water content obtained in filter paper with corresponding suction. A comparison on SWCC established through filter paper was also compared with that of the axis translation technique (pressure plate extractor). The study found that the initial water content and the density respectively, have great influence on the SWCC of compacted kaolin. However, the combined effect could be seen significantly at lower suction
8. Evaluation of Estimated Suction-Water Content Relationship for a Locally Available Soil
gndec.ac.in
Soil suction and its relationship with water content (gravimetric or volumetric) are inevitable in the study of unsaturated soil mechanics. Suction-water content relationship (designated as SWR), is an important input parameter for the mathematical modeling of unsaturated soil behavior response pertained to physico-mechanical, hydraulic, and volume change behavior. The experimental procedures adopted for determining SWR are time consuming and cost-intensive. Therefore, recent researches have laid a major focus on the indirect estimation of SWR. Such an estimated SWR can be used as initial guidelines for planning important geoenvironmental projects such as waste containment facilities. As such, it is important that these estimation procedures are precise and suitable for different type of soils. With this in view, effort has been made in this paper to critically evaluate an estimation procedure for a particular type of soil. The SWR has been established using two commonly adopted procedures. The study indicates that the estimated SWR does not match well with the measured SWRs for the type of soil investigated in this study.
Field and Laboratory Suction- Soil Moisture Relationship of Unsaturated Residual Soils
American Journal of Environmental Sciences, 2005
Soils located above the groundwater table such as residual soils are generally unsaturated and possess negative pore-water pressures. A soil-water (moisture) characteristic curve (SWCC) that relates the water content of a soil to matric suction is an important relationship for the unsaturated soil mechanics. The SWCC essentially shows the ability of an unsaturated soil to retain water under various matric suctions. It has a similar role as the consolidation curve of a saturated soil that relates void ratio or water content to effective stress. This study describes a study that has been carried in the field and in the laboratory to examine the suction-soil moisture relationship of unsaturated residual soils of granite and sedimentary rocks origin. The field measurement shows a decreasing trend of suction with depth for both soils. The suction-soil moisture relationship shows two distinct curves, a wetting (sorption) curve and a drying (desorption) curve. While from the laboratory study, it is observed that there is a significant decrease in the soil moisture with increasing suction in the lower suction ranges, until a de-saturation or air entry point for both soils. Beyond this point, the magnitude of the decrease in soil moisture for the equal increment of applied suction is less. The de-saturation point of a particular soil appears to be dependent on the amount of clay content. Higher amount of fines in the soil constitute a more compact particle arrangement and a smaller pore size. Soils with smaller pore sizes de-saturate at higher matric suction.