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Showing 8 results for Bentonite

Pakbaz M.c., Ahmadi C.,
Volume 1, Issue 2 (12-2003)
Abstract

This research include, more than 400 erosion tests performed on coarse and fine grain suspension materials. The purpose of tests was to determine erosion characteristics of mixtures of different materials. Samples of the .same constituents in different groups were cured tit two different setting time of // and 16 !tours before they were subjected to the constant hydraulic heads of 20 and 40 cm for ct time period of 30 urinates. The amount of erosion was measured as the weight loss of the samples offer the test. /n general the lower setting tune and the higher hydraulic head for a large group of samples showed higher erosion. For uniform sand samples when the cement content was 60-70 % the percentage of erosion (PE) was below 2. For the mixture of sand-cement, with the clay content below, 20% the percentage of erosion was below 2 and it increased to 15.5 for the clan, content of 58dc. Die addition of bentonite in the soil-cement mixtures in general did not affect the erosion.
Shooshpasha I.,
Volume 1, Issue 2 (12-2003)
Abstract

This study was designed to investigate the local volume changes induced by swelling pressure in unsaturated stand-bentonite bused buffer material. A laboratory mixture of sodium bentonite (lilt/ well graded silica stool in equal proportion by do weight was used for moisture floss experiments in both ambient and elevated temperatures. Experimental results have shown that tit high water content locations within the tested specimens, the density was reduced by .3.57% from its initial values clue to swelling. The swelling pressure was calculated by 4 different models as a function of distance. The calculated results have indicated that the density distribution within the .specimen is affected by swelling potential distribution. The calculated swelling pressure values van as u function of water content, reaching I MPa at the source of water intake, i.e., at high water content :.one, and 2 MPa cot the heater .side, i.e., cot low water content .one.
M. Naderi,
Volume 3, Issue 1 (3-2005)
Abstract

Having observed the costly failures of different cutoff walls, that had been constructed according to the mix design specified by reputable consultants in Iran, a research programme was conducted to study the effects of constituent materials on the properties of plastic concrete. The main properties, such as compressive strength, biaxial and triaxial strains, permeability, and modulus of elasticity have been investigated using different mixes, obtained from prototype production line plant, situated on site, because it was realized that the site production line and the systems employed have major effects on the properties of plastic concrete. Statistical analysis of the results, revealed the coefficients of influence of main constituent materials of plastic concrete namely cement, bentonite, aggregate and water on its compressive strength and modulus of elasticity. Having realized the cancelling effects of bentonite and aggregates on the measured properties, some equations relating the quantities of cement and water to the compressive strength and modulus of elasticity are introduced. Effects of clay and hydrated lime powder, as fillers were also investigated leading to the proposal of limits for their safe and economic use. Since most of the cutoff walls are buried structures, failure strains under both uniaxial and triaxial tests, with values of cohesion and internal friction, are also presented in this paper.
Mohammad C. Pakbaz, M. Lorestani,
Volume 3, Issue 2 (6-2005)
Abstract

The main purpose of this research is evaluation of effect of chemicals on permeability of sand- bentonite mixtures. The coefficients of permeability of sand- bentonite mixtures in water, solutions of sodium and calcium chlorides, sodium hydroxide, acetic acid, methanol and carbon tetrachloride were calculated using parameters obtained in 1- D consolidation test and Terzaghi’s theory. At each void ratio permeability of samples in water is the lowest and that for carbon tetrachloride is the highest. For all fluids the permeability index Ck is decreased as the percentage of sand is increased. The largest Ck belongs to the samples tested in water and the smallest Ck belongs to the samples tested in carbon tetrachloride.
Nader Shariatmadari , Marzieh Salami, Mehran Karimpour Fard,
Volume 9, Issue 2 (6-2011)
Abstract

The main task in the design and construction of impermeable liners in landfills is to block the migration of pollutants to the groundwater

systems or to reduce its rate to a reasonable amount. That is why environmental regulations force governments to construct engineered

waste dumps for waste management purposes. These liners are exposed to various types of chemical, biological, and physical processes

and are affected by the leachate which is produced from decomposition of waste materials accompanying methane gas. The leachate

includes a lot of components such as water and different types of salts. For this reason, the geotechnical characteristics of clay liners

which are evaluated in laboratories using distilled water or tap water might be far different from the representative sample of the in-situ

conditions. There are some evidences regarding the effect of these salts on the physical and mechanical properties of clay barriers which

could affect the long-term performance of these liners. Since the main criterion for impermeable bottom liners in landfills is their

hydraulics conductivity, the increase of this parameter could have a considerable environmental impact. This paper embraces the results

of a recent study on the effect of three inorganic salts, NaCl, CaCl2 and MgCl2 on some geotechnical properties of a common used clay

soil in impermeable bottom barrier in Kahrizak landfill, the main waste disposal center of the Tehran Metropolitan. Also the effect of

bentonite content by adding different percentage of this special clay mineral, 10 and 20 percent, on these properties was investigated.

Laboratory tests like liquid limit, compaction, 1D consolidation and free swell tests were performed for this purpose. Results indicated

that all of these salts could have a considerable effect on the geotechnical properties of the mixtures. The main reason of such effects is

the changes which occur in diffuse double layer of clay particles.


N. Shariatmadari, S. Saeidijam,
Volume 10, Issue 2 (6-2012)
Abstract

Bentonite-sand mixture is one of the most important candidates for engineering buffer element in nuclear waste repositoriesso
the analysis of its thermo-hydro-mechanical behavior is important for design purposes.An innovative setup of classic oedometer
was used for swelling and compression study at high temperatures in this research. A fully calibration program was utilized to
include high temperature effects on measurements. This research shows that the elevation of temperature from 25 to 90◦C in
1:1bentonite-sand mixture in distilled water reduces free swelling potential and strain about 20 percent. The required time for
equalization of swelling is less in high temperature due to increasing in permeability. Also, the high temperature causes increasing
in compressibility rate and quantity for this buffer. For detection of this effect, XRD analysis showed that an increase in
temperature causes a decrease in basal spacing. So, the particles can come near to each other more than lower temperatures and
the amount of absorbed water in the microstructure of the clay is smaller.The effect of thermal history on behavior of bentonitesand
mixture has been showed and tried to clarify it. At similar stress-temperature states, thermal history causes different
deformation in samples. The highest temperature that bentonite has been experienced, controls its behavior in the next thermal
cycles.


M. Fadaee, M.k. Jafari, M. Kamalian, M. Moosavi, A. Shafiee,
Volume 11, Issue 2 (11-2013)
Abstract

During past earthquakes, many instances of building damage as a result of earthquake surface fault rupture have been observed.

The results of investigating a potential mitigation scheme are presented in this paper. Such plan provides a wall in the soil with

the aim of surface displacement localization in the narrow pre-determined location. This may reduce the risk of the future rupture

downstream the wall. To evaluate the efficiency of the method, this paper (i) provides validation through successful class “A”

predictions of 1g model tests for fault deviation by weak wall and (ii) conducts sensitivity analyses on fault position, fault offset

and wall shear strength. It is shown that wall can be designed to deviate rupture path even downstream of the wall can be

protected.


A. H. Eghbali, K. Fakharian,
Volume 12, Issue 1 (1-2014)
Abstract

Portland cement can be mixed with sand to improve its mechanical characteristics. Many studies are reported in literature on this topic, but the effect of principal stress rotation has not been investigated yet. Considering the inherent anisotropy of most sands, it is not clear whether the added cement shall contribute to equal increase in strength and stiffness at vertical and horizontal directions or not. Furthermore, it is not well understood how the cement as an additive in non-compacted (loose) sand compared to compacted (dense) sand without cement, contribute to improving the material behavior in undrained condition such as limiting the deformations and the liquefaction potential. In this research, undrained triaxial and simple shear tests under different stress paths are carried out on different mixtures of Portland cement (by adding 1.5, 3 and 5 percent) with clean sand to investigate the effect of principal stress rotations. The triaxial test results revealed that the cement mixture reduces the anisotropy, while it improves the mixture mechanical properties compared to compacted sand without cement. The results of the simple shear tests validated the triaxial test results and further clarified the effect of the  parameter or rotation of principal stresses on the behavior of cemented sand mixtures.

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