Predicting Swell in Clay-Sand Mixtures Used in Liners

Advances in Materials Science and Engineering

Sand-clay liners utilize expansive clay to act as a filler to occupy the voids in the sand and thus reduce the hydraulic conductivity of the mixture. The hydraulic conductivity and transfer of water and other substances through sand-clay mixtures are of prime concern in the design of liners and hydraulic barriers. Many successful research studies have been undertaken to achieve appropriate mixtures that satisfy hydraulic conductivity requirements. This study investigates compressibility and swelling properties of mixtures to ensure that they were acceptable for light structures, roads, and slabs on grade. A range of sand-expansive clay mixtures were investigated for swell and compression properties. The swelling and compressibility indices were found to increase with increasing clay content. The use of highly expansive material can result in large volume changes due to swell and shrinkage. The inclusion of less expansive soil material as partial replacement of bentonite by one-third...

International journal of GEOMATE : geotechnique, construction materials and environment, 2020

This paper investigates the effect of adding low percentages of cement on the swelling and compressibility characteristics of sand-expansive clay mixtures. The use of highly plastic clay is known for reducing the hydraulic conductivity which is the main goal of waste containment barriers. However, liners can act as cover layers, road base, or a supporting ground. Excessive swell is likely to cause damage to light structures. Recent studies called for using clay with low plasticity that is just enough to fill the voids. Other researchers suggested adding fillers of fine powder. This study is an attempt to reduce the high plasticity with the addition of cement. The expansive clay used in this research was obtained from Al-Qatif region in the Eastern Province of Saudi Arabia. For these mixtures, the sand was considered the host material, and the clay content varied between 10% to 40% by dry weight of sand. The proposed cement content is put as low as 1, 2, and 4% by the dry weight of mixture at curing periods of 1, 7, and 28 days. A series of onedimensional odometer tests were conducted to evaluate the swelling potential, swelling pressure, and compressibility characteristics of mixtures. Laboratory compaction tests were performed to determine optimum moisture content and maximum dry density. The addition of cement was found to improve the engineering properties of the mixtures and stabilize and control the swell and compressibility of the liner material

EJGE, 2008

This study investigates the swell characteristics of a highly plastic clay in its natural state and after this clay was separately treated with potassium and calcium chlorides. Free swell tests were conducted on these three (natural and treated) soils at two different temperatures (26°C and 40°C) This study shows that a linear relationship exists between the percent free swell and the liquid limit for the tested soils at given water content, dry density, and temperature and also shows that these soils are not susceptible to expansion when the liquid limit drops below about 40 % regardless of the initial states of water content and dry density as well as test temperature. This study confirms that the percent free swell may reliably be modelled by a rectangular hyperbolic equation as a function of time and liquid limit. The influence of temperature on the swell potential are observed to be dependent on initial compaction states.

Scientific Reports

This study investigated shear strength behaviour of compacted sand–clay mixtures used as liners, with 10%, 20%, and 30% clay contents. A natural high-plasticity and highly expansive clay found in the eastern province of Saudi Arabia was used. A series of consolidated undrained triaxial tests and pore water pressure measurements of saturated samples with various clay contents and confining pressures was conducted using a computer-controlled Bishop and Wesley triaxial cell. The unit was equipped with pressure volume controllers and a pressure transducer for measuring sample volume changes and excess pore water pressure. The experimental test results indicate that clay content and confining pressure significantly affect stress strain response curves, pore water pressure generation curves, and steady-state shear strength. Sand–clay mixtures with clay content less than 10% showed a tendency toward contractive behaviour. The failure line slope increased in accordance with clay content inc...

Revue des composites et des matériaux avancés, 2022

The influence of initial moisture content and dry density on swelling clays was extensively investigated in the literature. In order to explore the relationships that exist between the swelling parameters of clay soils and the water content, initial dry density, and sand content, a series of experimental tests were conducted on pure clay and clay treated with 20% sand. The swelling pressure and the swell potential were also tested for sand-clay mixtures. The results showed a significant influence of the initial water content on the swell potential of bentonite and bentonite sand mixture. The increase in the dry density was found to boost the swelling pressure and swell potential. The rate of increase is related to sand content. For higher sand content, it was found that grain-to-grain contact reduces the compressibility of the mixture and thus causes the general swell trend to alter. The amount of clay particles within the mixture is an important factor affecting the swelling. The results demonstrated the effectiveness of the sand in the reduction of swelling parameters. This study provides a control measure for expansive soil materials using sand addition to achieve better soil for construction purposes.

Arabian Journal of Geosciences, 2020

The main object of this research is the investigation of the behavior of clay-sand mixtures in undrained condition. For this purpose, the behavior of clay mixed with the different percentage of sand (i.e., 0%, 20%, 40%, and 60%) was studied by carrying out undrained triaxial tests on normally consolidated and overconsolidated specimens under different effective stresses. The results showed that sand inclusion up to 20-40% (depend on sand size) does not affect considerably the shear strength of the clay, but when the amount of sand is more than 40%, the shear strength raises 74 to 260%. Maximum pore water pressure at low confining pressures remains unchanged by changing sand content from 0 to 60%. At high confining stress, this parameter for specimens consists of 40% sand is higher than the corresponding values of the other ones. For overconsolidated specimens, irrespective of some exceptions, dependent on sand size, the values of shear strength improve 43 to 73% when sand content varies from 0 to 60%. In addition, deformation modulus of both normally consolidated and overconsolidated mixtures increases 9 to 136% by an increase in sand content from 0 to 40%, and, then, the values diminish rapidly by changing sand content from 40 to 60%.

Ksce Journal of Civil Engineering, 2017

Three laboratory models were designed to simulate a field section of a clay sand liner. The laboratory models were designed to test 10 cm thick Al Qatif clay sand liners with clay content of 15%, 20% and 25% overlain by agricultural soil and underlain by granular sandy material. The percolation through the clayey layer was measured for repeated watering following variable drying periods. 30 tests were conducted for each clay content over a period of 3 to 4 months in a laboratory controlled environment. Temperature, moisture and electrical conductivity were recorded using 5TE sensors. The hydraulic conductivity and soil water characteristics of the material used in the liners were studied. It was found that the soil suction and drying are related to non-uniform performance of the liner on repeated drying and wetting. The results of a theoretical model using Hydrus 2D for a similar section subjected to different environmental conditions indicated that liners can significantly reduce percolating water. The laboratory model confirmed the findings. The temperature drop below the ambient laboratory value was found 1.0ºC for the 15% clay and 0.6ºC for 20% and 30% clay liners. The trends of moisture gain and drop were shown.

Academia Biology, 2023

Wildlife abundance can be very difficult to estimate, especially for rare and elusive species, such as wolves. Over nearly a century, wolf scientists have developed methods for estimating abundance across large areas, which involve marked animals being detected again after capture, sometimes supplemented by observations of the associates of those marked animals. Recently, several US jurisdictions have departed from those proven methods to explore alternatives that are believed to be less expensive for wolf populations estimated >1000 individuals. The new methods sacrifice precision but are believed to retain adequate accuracy and sensitivity to changing conditions for reliable decision-making. We review evidence for the accuracy, precision, sensitivity, and reproducibility of the new “scaled occupancy model” (SOM) applied in Wisconsin. We conclude that the Wisconsin method would systematically overestimate wolf abundance by large (but currently incalculable) margins. Because Wisconsin, similar to other states, not only changed to unverified methods but also implemented widespread wolf-killing, shortcomings in their estimates of wolf abundance may have far-reaching consequences for population viability and confidence in state wildlife policy. We discuss findings from Wisconsin alongside similar findings for other states’ occupancy models being insensitive to human causes of mortality that have recently increased. Overall, Wisconsin’s method for estimating wolf abundance shows significant departures from best practices in scientific measurement. Verification will require independent replication and unbiased tests at multiple scales in multiple habitats under different human-induced mortality rates and rigorous independent review before the new methods are considered reliable.

Annales Theologici, 2021

In the first centuries of Christianity many writings appeared bearing the title “Gospel” yet only four of them ended up being recognized as such and as worthy of being read, copied, revered and transmitted through the ages until our day. The rest were considered spurious and most ended up being lost to posterity. Thanks to the new-found interest in archeology in the 19th and 20th centuries, many of them have been found and made available for scholarly study. One of these—the Gospel of Thomas—has received a great deal of interest mainly due to its similarity both in its form to the hypothetical document “Q” of the two source theory behind the formation of the synoptic Gospels, as well as in some of its contents to some of the sayings of the Lord found in the canonical Gospels. That of course raises the question: why was the Gospel of Thomas not included among the canonical Gospels? In this paper, we will examine the concept of “Gospel” in a bid to elucidate what it is that was found to be common to the 4 canonical Gospels and yet lacking in the Gospel of Thomas, so much so that, despite the similarities with the other four, it ended up being altogether rejected.