Effect of clay minerals on the suction stress of unsaturated soils (original) (raw)
Related papers
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.
Lack of consideration in unsaturated soils behaviors namely volume change and collapse have caused lots of damages to foundations, buildings, and other structures. Such behaviors are related to drying and wetting phenomena. This paper presents results from triaxial tests on unsaturated clayey soil of Yasouj subjected to drying and wetting cycles using a modified triaxial equipment. Various levels of matric suction ((− −) and net normal stress ((−) were applied on the unsaturated specimens. The results indicated that under a similar stress level, the void ratios of samples under suction were significantly greater than the void ratio of sample which was not under suction (saturated sample). It was also observed that at constant matric suction, the collapse potential of the soil increased initially to a maximum value with increasing net mean stress and then decreased at very high net mean stress. At any constant net normal stress, the soil collapsed upon wetting due to a reduction in m...
Influence of Mineral Montmorillonite on Soil Suction Modeling Parameters
GeoCongress 2012, 2012
Expansive soils exhibit swell/shrink behavior with fluctuating moisture conditions arising from seasonal changes. Pore-water interactions occurring at the micro scale level of the soil specimen during swelling are mainly caused due to adsorptive forces and diffuse double layer charges on the clay particles. This chemical behavior is mainly attributed due to the presence of clay minerals such as Montmorillonite and is hypothesized that there is a strong correlation between soil water-suction relationship and percent clay mineral Montmorillonite. In the present research, an attempt is made to establish this relationship by studying natural compacted expansive clays and studying their respective soil water characteristic curve (SWCC). Four high plasticity expansive clays are selected and studied for mineralogy, expansive behavior and unsaturated properties. Soil water characteristic curves of these soils are determined from pressure cell technique and filter paper method. SWCC data was fitted against Van Genuchten and Fredlund and Xing models and the obtained model parameters are compared with the percent clay mineral in the soil. Test results from this research reemphasized the fact that that clayey soils with higher percentages of Montmorillonite content exhibited higher swelling behavior. Test results also showed that there is inconsistency with pore distribution SWCC modeling parameters with varying mineral content. Addressing the relationship between the percent Montmorillonite in a soil to SWCC modeling parameters is the main outcome.
SUCTION VARIATION OF NATURAL AND TREATED UNSATURATED GYPSEOUS SOILS DURING WETTING
2023
There are several soils all around the world that collapse (experience significant settlement) when unusually subjected to amounts of water. Collapsible gypseous soil is one of the wide varieties of problematic soils. The gypseous ground can be found in dry and semi-arid areas. Here, gypsum deposits are common such as in Iraq. Gypseous grounds are considered as collapsible or metastable soils, considered any type of unsaturated soil, which reveals a radical rearrangement of soil particles and is disposed to a significant change in volume. Collapses occur when soils are wetted with water. This may additionally occur if soils are socked under loading [1, 2]. Gypsum is a hydrated calcium sulfate mineral CaSO4.2H2O having an intermediate solubility of 2.6.g/l at 25 ºC [3]. When the soil is dry, the gypsum in the soil structure functions as cement. Studying the properties of unsaturated soil with gypsum is a challenging problem in many geotechnical engineering applications, such as dams, strata under pavement, and foundations [4]. The field of soil mechanics in general, could be divided into a portion dealing with saturated soils and another dealing with unsaturated soils. Due to fundamental distinctions in their nature and engineering behavior, saturated and unsaturated soils must be distinguished from one another. In unsaturated soil, there are more than two phases, and the pore-water pressure is negative compared to the pore-air pressure. The main geotechnical problems connected to these soils are that when the soil gets wet, the pore pressure decreases, the effective stresses are concentrated, volume changes, and decreasing the soil's shear strength. Moreover, water can soften the soil particles' bonds, enabling denser packing. Negative pore-water pressures and ability desaturation could be influenced any soil near the ground surface that is present in a dry environment. The processes of remoulding, excavating, and recompacting soil also produce unsaturated material. These materials comprise a significant proportion of soils that are typically challenging to analyze within the framework of traditional soil mechanics. [5]. Suctions in unsaturated soils may vary greatly (from zero to 10 6 kPa), as a result of reactions to imposed weather conditions. If the suction pressure is considered, it is possible to understand better the engineering behavior of soils within an unsaturated state [6]. Suction stress plays an obvious function in the unsaturated soils' behaviors, shear strength, permeability, and volume change. The total amount
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.
Total and Matric Suction in Unsaturated Soil with the Existence of Different Salts Content
Engineering and Technology Journal, 2013
Soils located above the groundwater table are generally unsaturated and exhibit negative pore-water pressures. A soil-water 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. The filter paper method is a soil suction measurement technique. Soil suction is one of the most important parameters describing the moisture condition of unsaturated soils. The measurement of soil suction is crucial for applying the theories of the engineering behavior of unsaturated soils. In this paper, three soil samples were collected from three sites within Baghdad city in Iraq. These soils have different properties and they were prepared at different degrees of saturation. For each sample, the total and matric suction were measured by the filter paper method at different degrees of saturation. The ...
The effect of soil mineralogy and pore fluid chemistry on the suction and swelling behavior of soils
Bulletin of Engineering Geology and the Environment, 2014
Soil suction is one of the most important parameters for describing the moisture condition and engineering behavior of unsaturated soils. Therefore, changes in suction behavior of soils in the presence of saline waters are important for engineered barriers. The aim of this study was to determine the change in suction and swelling behavior of soils, which were exposed to salt solutions (NaCl, CaCl 2 , natural seawater) with respect to distilled water. The three soil samples were gathered with different mineralogy and plasticity characteristics and tested for determining matric and total suction values and for obtaining free swelling characteristics in the presence of salt solutions. The bentonitic soil sample had the highest total suction value in the presence of seawater. Kaolinitic and zeolitic soil samples had the highest total suction values in the presence of NaCl solution. The highest modified free swell index value of the samples was obtained in the presence of NaCl solution for all the soil samples. No relationship was found between the total suction, matric suction and the modified free swell index value of the tested soils.
Suction effects on the tensile strength and unconfined compression of unsaturated soils
MATEC Web of Conferences, 2021
The soil-water characteristic curve is an important relation of unsaturated soils, that expresses the variation of the amount of water retained in the soil as a function of its suction. In these soils, drying or wetting can have a great influence on their resistance parameters. This work presents and discusses the effects of increased suction on the tensile strength and unconfined compression of unsaturated soils. Suction was evaluated using the filter paper and the dew point technique, while the resistance parameters were obtained through the "Brazilian Test" and uniaxial compression. Three different soils from Rio de Janeiro were studied: two young residual soils, in which the influence of the soil structure was also verified through tests on undisturbed and reconstituted samples, and a colluvial soil. The results allowed to conclude that the increase of suction, in a first moment, generates an increase in the resistance parameters of these soils. With the continuation o...
Soil-Water Charateristics of Tropical Clay Soil under High and Low Suction Conditions
Journal of Geoscience and Environment Protection, 2020
Tropical clay soil was compacted at different moisture conditions (dry, wet and optimum) and compactive efforts (Reduced proctor, Standard proctor, West African standard and Modified proctor). Experimental Soil-Water Characteristics (SWC) of the soil was derived using the pressure plate extractor equipment and SWC Curves (SWCC) plotted as gravimetric water content versus logarithm of matric suction. The Air Entry Values (A.E.V) obtained from experimental work ranged from 21 kPa to 59 kPa and compared favourably well with those estimated from predictive models with values of 23 kPa to 52 kPa. Specimens compacted with greater compactive effort (Modified proctor) and at optimum moisture content produced the largest air entry value of 59 kPa and reduced air voids. Changes observed in the shape of the SWCC were consistent with changes in pore size which occurred by varying compaction conditions. The shape of the soil-water characteristics curve was found to depend on the soil structure, compactive water content and compactive effort and not solely on the percentage of fine particles.