Optimization of Sand-Bentonite Mixture for the Stable Engineered Barriers using Desirability Optimization Methodology: A Macro-Micro-Evaluation (original) (raw)
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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.
Physical and mechanical properties of a compacted silty sand with low bentonite fraction
Canadian Geotechnical Journal, 1998
Compacted granular soils with small additions of bentonite have been used to build geotechnical structures such as impervious liners and cores of zoned earth dams. This paper presents a laboratory study showing how physical and mechanical characteristics of a silty sand are modified by a low percentage of bentonite. The effects of the addition of bentonite on the silty sand are reflected by an increase in the plasticity index, a reduction in maximum modified Proctor density, and a decrease in hydraulic conductivity. The most significant consequences on the mechanical properties are an increase of compressibility and secondary consolidation coefficients, and a reduction in shear strength. Different mixtures were either dynamically compacted at the optimum water content (compacted samples) or prepared after slurry consolidation from the minimum density (remoulded samples). Although the compacted and remoulded specimens show different isotropic compression lines, their critical-state lines in the v:p ′:q space are identical, where v is specific volume, p′ is average effective stress, and q is deviator stress. Comparisons of the mechanical parameters with the existing literature database show that the compression coefficients of the remoulded mixtures are comparable to those of normally consolidated clayey soils of similar plasticity; nevertheless, those of the compacted mixtures are considerably lower. Also, the slopes of their critical-state lines in the q:p ′ plane are in good agreement with those predicted by empirical correlations for fine-grained soils.
A Study on Compressibility, Swelling and Permeability Behaviour of Bentonite–Sand Mixture
2019
In geotechnical engineering field, bentonite–sand mixtures have been proposed and used as engineered barriers for containing the waste. This paper presents the laboratory evaluation of compressibility by performing one-dimensional consolidation tests on six different mixtures of bentonite with sand. The bentonite–sand mixtures were formed by varying sand content in bentonite in increments of 5% from 5 to 25% by dry weight. Dry bentonite–sand mixtures were placed initially in the consolidation cell at their loosest dry state and then allowed to saturate. Swelling characteristics and swelling pressures of the bentonite–sand mixtures were also evaluated. This paper also presents the laboratory evaluation of permeability of the bentonite–sand mixtures by performing falling head test after every load increment during the consolidation test. This study arrived at the conclusion that amount of swelling (expressed in percentage) and swelling pressure decreased with addition of sand. Moreove...
Evaluation of the Permeability Behaviour of Sand-Bentonite Mixtures Through Laboratory Tests
Indian Geotechnical Journal, 2012
In recent years, when suitable impervious soils are not available for containing the waste, barriers constructed using sand-bentonite mixtures are being frequently adopted to contain the waste. This paper presents the laboratory evaluation of permeability of sand-bentonite mixtures through falling head tests performed with rigid wall permeameter and oedometer on different categories of sand-bentonite mixtures. Five different categories of sandbentonite mixtures were formulated by varying bentonite content in increments of 5 % from 5 to 25 % by dry weight. Atterberg limits and compaction characteristics of sand-bentonite mixtures were evaluated. With an increase in bentonite content, the unconfined compressive strength of the sand-bentonite mixture was found to increase linearly and a sharp decrease in permeability was registered up to a bentonite content of 15 % and beyond this the decrease in the permeability was marginal. Permeability tests were carried out with and without prior saturation of the samples. It was found that permeability behavior of sandbentonite mixtures was affected by the initial saturation process and type of permeability testing method.
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.
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.
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.
Maǧallaẗ al-handasaẗ wa-al-tiknūlūǧiyā, 2016
Expansive soils are generally found in arid and semiarid regions. These soils undergo volumetric changes upon wetting and drying, thereby causing ground heave and settlement problems. This characteristic causes considerable construction defects if not adequately taken care of. Solving the unsaturated soil problems needs the assessment of suction variation in time and space as a response to the variation of environmental factors such as rainfall and evaporation. To investigate the effect of the changes of the soil suction on the volume changes, expansion index, swelling pressure, shear strength and the coefficient of permeability, small scale experiments were conducted using pure bentonite and the bentonite mixed with sand in proportion of: 30%, 40% and 50% at different initial water contents and dry unit weights was chosen from the compaction curves. The study shows that the swelling-potential, swellingpressure, the soil-suction, the soil-strength and the coefficient of permeability are affected by the initial-conditions (water-content and dry-unit weight), where all these parameters except the permeability-coefficient marginally decrease with the increase in soil-water content, while the coefficient-of permeability increases with increasing the water-content.
Compacted sand–bentonite mixtures for the confinement of waste landfills
Acta geotechnica, 2024
This paper illustrates the results of an experimental study on sand-bentonite mixtures for their use as confinement barriers for solid waste landfills. The mixtures have been prepared parametrically varying the percentage of bentonite. The sample preparation method was established willing to simulate the compaction processes on site. In fact, the compacted samples were tested following two different stress-wetting paths representative of the possible stress and imbibition sequences occurring on a landfill confinement barrier. In the first case, the barrier comes into contact with rainwater before being subjected to the overloading stress induced by waste disposal, while, in the second case, the barrier is overloaded by the waste before being wetted by the leachate. The compressibility and permeability of the sand-bentonite mixtures were determined, in both cases, by oedometric compression tests. The experimental results are analysed and compared in order to evaluate the influence of the bentonite content on the mechanical and hydraulic behaviour of the mixture. Interpretation of the results is also accomplished with a micro-mechanical investigation of the mixtures fabric. Suitable compositions of sand and bentonite are finally proposed for the design of effective confinement barriers. Keywords Bentonite compaction Á Bentonite swelling Á Bentonite hydraulic conductivity Á Compaction of sand-bentonite mixtures Á Hydraulic conductivity of sand-bentonite mixtures Á Oedometer test on bentonite Á Oedometer test on sandbentonite mixtures Á Sand-bentonite mixtures Á Swelling of sand-bentonite mixtures Á Waste landfills confinement & Erminio Salvatore