Physical and mechanical properties of a compacted silty sand with low bentonite fraction (original) (raw)

Geotechnical Characteristic of Compacted Sand Bentonite Mixture

International Journal for Research in Applied Science and Engineering Technology

Sand and bentonite mixture is generally used as a liner or backfill material at waste disposal sites and construction of hydraulic barriers. Bentonite is added to sand to achieve a higher compaction density and lower shrinkage. Permeability and strength are important properties of sand-bentonite mixtures and are often required for the design of the liner/barrier of the containments. A review of the literature showed that most of the past research work has focused on studying the influence of bentonite on the various geotechnical properties of sand-bentonite mixtures. In this study, the permeability, and strength characteristics of sand-bentonite mixture is investigated to support recommendation for a cost-effective liner material with locally available soil. Locally available Narmada sand of Jabalpur, Madhya Pradesh (India) was mixed with different proportions of sodium bentonite. A series of standard tests such as Modified Compaction test, Unconfined Compression Strength (UCS) test and Permeability test for strength and hydraulic conductivity characteristics, were conducted on different of sandbentonite mixtures. The mixtures were formed by mixing local sand, with (0%, 5%, 10%, 15%, 20% and 25%) by dry of sodium bentonite. The investigations are presented to show the influence of bentonite clay on compaction, Atterberg limits, FSI, UCS, and permeability of Narmada sand by increasing the bentonite content 5% by weight each time. It was found that there is significant improvement in MDD and OMC of sand-bentonite mixture. This study focuses on the effect of bentonite content on strength and permeability, which are two important requirements of hydraulic liner material, of sand-bentonite mixtures.

Predicting the Properties of Bentonite-Sand Mixtures

Clay Minerals, 1996

One-dimensional swelling tests and hydraulic conductivity tests have been performed at vertical effective stresses up to 450 kPa on Na-bentonite powder and compacted sand/Na-bentonite mixtures (5, 10 and 20% bentonite by weight) to investigate the use of bentoniteimproved soils for waste containment. It was found that bentonite powder swells to reach a final state described by a single straight line on a plot of void ratio against the logarithm of vertical effective stress, regardless of preparation technique. Swelling of sand/bentonite mixtures expressed in terms of the clay void ratio show a deviation from bentonite behaviour above a stress which depends on the bentonite content. Hydraulic conductivity data for bentonite and sand/bentonite mixtures indicate an approximately linear relationship between logarithm of hydraulic conductivity and logarithm of void ratio. A design model based on the clay void ratio, and the sand porosity and tortuosity is presented enabling the hydraulic conductivity of a mixture to be estimated.

Permeability and swelling characteristics of bentonite

International Journal of the Physical Sciences, 2010

Permeability and swelling characteristics of bentonite and bentonite-sand are the essential parameters for designing any type of waste disposal or in geo-environmental engineering applications. To design and construct these facilities accurate values of permeability for these bentonite-sand mixtures must be evaluated. For this purpose, a series of various laboratory tests were performed to investigate the coefficient of permeability using direct and indirect test methods derived from consolidation theory using liquid limit 1.5 of bentonite. Permeability tests were also carried out for dynamically compacted bentonite. Void ratio of bentonite is a key parameter of permeability for bentonite and bentonite-sand mixtures. The specimen manufacture method had no effect on permeability. A series of swelling pressure and deformation tests are performed using variable content (30 to 90%) of bentonite at initial dry density of 2 g/cm(3) to investigate the characteristics of buffer material for radioactive waste disposal. Content of bentonite in bentonite-sand mixture is the prime criteria of buffer material and must be taken into consideration in designing any types of waste disposal facilities. Content of bentonite and loading pressure on the specimens is noticeably influenced on maximum swelling rate.

The Permeability and Shear Strength of Compacted Claystone–Bentonite Mixtures

International Journal of GEOMATE, 2021

A compacted claystone-bentonite mixture is proposed for use as a clay barrier. This research, in turn, focuses on the effects of bentonite mix on the permeability and shear strength of compacted claystonebentonite mixtures. The claystone used was obtained from the Banjarbakula landfill project, approximately 10 km from Banjarbaru, the South Kalimantan Government's Administrative Center, Indonesia. The bentonite used is commercially sold in Indonesia. The claystone was mixed with bentonite at a percentage of 5%, 10%, 15%, and 20% bentonite by dry-weight bases. The mixtures were compacted at a moisture content of 10%, 15%, and 20% to reach the dry unit weight of 16kN/m 3-19kN/m 3. Permeability and unconfined compressive strength tests were performed in this study. The result showed that the permeability of mixtures decreases with increasing bentonite content. The addition of up to 20% bentonite to the mixture reduced the permeability by 4.5 times, as compared to the sample without bentonite. Moreover, the mixtures' shear strength indicated by compressive strength and cohesion increased by increasing the bentonite content to 15%. The maximum shear strength obtained was three times higher than without bentonite. The mixtures' permeability and shear strength were also significantly affected by the sample's density and moisture content. A percentage of 20% bentonite is recommended, considering the wide range of acceptability based on two criteria (i.e., permeability and shear strength).

A parametric study on the hydromechanical properties of claystone/bentonite mixtures

E3S web of conferences, 2023

Mixtures of crushed excavated COx claystone and bentonite are considered as a potential backfill solution for the French disposal concept of radioactive waste. In the present work, the hydro-mechanical behaviour of claystone/sodium bentonite mixtures was experimentally investigated for various bentonite contents (≤40% in total mass) and densities. Demineralized, site water and cementitious alkaline solution were used. Test on mixtures physicochemical properties showed that Plasticity Index (PI) and Free Swelling Index (FSI) values increase with bentonite content. Introducing bentonite in the mixture induces to lower density for the same compaction energy. No clear impact of the cementitious solution was observed compared to the site water. The expected swelling pressure increase upon bentonite increment was obtained. The effect was more important at higher densities. Mixtures primary wetting, resulted in lower swelling pressure.

The Effect of Curing Period on Strength Behaviour of Sand Bentonite Mixes

A landfill is a secured engineered pit in the ground into which the wastes are dumped. Proper landfill liners need to be used to avoid any hydraulic connections between waste and surrounding environment. These liners can be created of different materials of which sand-bentonite mixtures are attracting greater attention. The sand bentonite mixture is a mixture of two different materials in terms of their particle size and chemical activity to produce a material with low hydraulic conductivity, low compressibility and sufficient strength. Low hydraulic conductivity of the mixture is due to the ability of bentonite particles to swell and fill the voids between the sand particles and whereas sand framework provides low compressibility. In this work, 80% sand and 20% bentonite were taken for the sand-bentonite mixture, on which various preliminary tests and secondary tests were carried out to study the properties of the mixture. The Optimum Moisture Content (OMC) and Maximum Dry Density (MDD) were determined by Standard Proctor Test. Variation of unconfined compressive strength with curing period as well as with the water content on sand-bentonite mixture were obtained from the results of the tests performed in order to get the optimum curing period and water content. Hence, a suggestion can be made as to when the maximum Unconfined Compressive Strength (UCS) will occur at a particular curing period.

Hydraulic and mechanical properties of compacted bentonite after 18 years in barrier conditions

Applied Clay Science, 2018

The FEBEX "in situ" test was performed at an underground laboratory in Grimsel (Switzerland) with the aim of studying the behaviour of components in the near-field of a nuclear waste repository. A gallery of 2.3 m in diameter was excavated through the granite and two heaters, simulating the thermal effect of the wastes, were placed inside, surrounded by a barrier of highly-compacted bentonite blocks. In 2015, after 18 years of operation, the experiment was dismantled. Some of the bentonite samples taken were tested in the laboratory to characterize, among others, their physical state and determine their permeability and swelling capacity. There were significant changes in water content and dry density across the bentonite barrier: their distribution was radial around the axis of the gallery, with the water content decreasing from the granite towards the axis of the gallery and the dry density following the inverse pattern. The swelling capacity of the samples was related to their position in the barrier. In the internal, drier part of the barrier an increase of the swelling capacity with respect to the reference bentonite was detected, whereas the samples from the external part swelled less than expected. This was attributed to the different salinity of the samples. The hydraulic conductivity was mainly related to the dry density of the samples and decreased with respect to the reference bentonite. This decrease was not related to the position of the samples and could be related to the microstructural reorganization of the bentonite during the 18-year operation-which brought about an average decrease in the pore size-and to the low hydraulic gradients applied to determine the permeability of the samples retrieved.

Suitability of Bentonite Clay: An Analytical Approach

Earth Sciences, 2013

Bentonite is a type of clay with a very high proportion of clay mineral montmorillonite, resulting from the decomposition of volcanic ash. With high plasticity, Bentonite is highly water absorbent and has high shrinkage and swelling characteristics. Bentonite slurry is often used to solve problems in the construction of borings or excavating trenches in water-saturated soils. Over time, the uses of bentonite spread into more current applications including papermaking technology, cutoff walls, wastewater purification and even into different aspects of nano-technology because of nano-sizes of bentonite particles. Due to its vast engineering applications, it is of highly research interest. In this present study, an analytical approach has been made to find a suitable bentonite sample from three different types of bentonite samples (China, Pakistan and India) by analyzing their engineering properties and economy as well. Finally, China Bentonite sample is found to be most suitable with good engineering properties and economy than other samples.

The effects of technological voids on the hydro-mechanical behaviour of compacted bentonite–sand mixture

Soils and Foundations, 2013

Compacted bentonite-based materials are often used as buffer materials in radioactive waste disposal. A good understanding of their hydro-mechanical behaviour is essential to ensure the disposal safety. In this study, a mixture of MX80 bentonite and sand was characterized in the laboratory in terms of water retention property, swelling pressure, compressibility and hydraulic conductivity. The effects of the technological voids or the voids inside the soil were investigated. The technological voids are referred to as the macro-pores related to different interfaces involving the buffer material, whereas the voids inside the soil is referred to as the common macro-pores within the compacted bentonite/sand mixture. The results obtained show that at high suctions, the amount of water absorbed in the soil depends solely on suction, whereas at low suctions it depends on both suction and bentonite void ratio. There is a unique relationship between the swelling pressure and the bentonite void ratio, regardless of the sample nature (homogeneous or not) and sand fraction. However, at the same bentonite void ratio, a higher hydraulic conductivity was obtained on the samples with technological voids. The effect of sand fraction was evidenced in the mechanical yield behaviour: at the same bentonite void ratio, the bentonite-sand mixture yielded at a higher pre-consolidation stress.