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Volume 3, Issue 1 (11-2009)

(Paper pages 543-562) When two solutions are mixed, concentrations in the mixture are volume-weighted averages of the two end-members, but the thermodynamic activities of the species controlling the water–mineral reactions are non-linear functions of the mixing ratio. Therefore, two end member solutions in equilibrium with carbonate phase could lead to a mixture undersaturated with respect to carbonate. A favorite place for this phenomenon is water table, where mixing of different waters is taking place. In this paper, Porosity change in freshwater lens of an island was calculated by coupling dissolution potential with a variable density flow and solute transport model. The effect of permeability enhancement on the rate of porosity change was evaluated. Dissolution due to this mixing takes place in water table and active edge of freshwater lens (40m from coastline). The results indicate an increase rate of 0.6×10-3 percent of porosity per year. Permeability enhancement increases the rate of dissolution and porosity change in fresh water lens.
N Shariatmadari, M.mehdi Yazdanpanah, Saeid Saeidijam,
Volume 8, Issue 3 (12-2014)

Saline sea water, groundwater into salt domes or municipal waste leachate can affect hydro-mechanical properties of bentonite as a sealing material in nuclear waste repositories or landfills. This paper investigated the effect of sodium chloride solution on Atterberg’s limit, swelling, consolidation and permeability of bentonite. Swelling and consolidation test had been done at 0.05, 0.1, 0.5 and 2 molar solution and pure water by oedometer apparatus in Iran University of Science and Technology. Considering the results, it can be seen that a little increase in concentration of the solution reduces swelling of bentonite. So that the swelling potential of bentonite reduced from about 82% to about 1.5% by increasing in concentration of the solution from pure water to 2 molar solution. Liquid limit and plastic index of bentonite were reduced by increasing concentration of the solution but plastic limit was not changed significantly. Meanwhile increased concentration of the solution will facilitate reaching equilibrium for swelling and consolidation of the samples which occur due to their enhanced permeability. Permeability of bentonite increased about 7 times by increasing in concentration of solution from pure water to 2 molar solutions. Also, the Compressibility of bentonite was reduced by increasing in concentration of sodium chloride in the solution.
Mh Ghobadi, R Babazadeh,
Volume 10, Issue 1 (8-2016)

Strength and durability of sandstones and their influences from natural conditions, are the most important factors which should be considered as engineering materials. In this study, the effect of freeze-thaw and salt crystallization phenomena on strength and durability of upper red formation sandstones collected from southern part of Qazvin province was investigated. Nine specimens of sandstones (specified by A, B, C, CG, S, S1, Tr, Min and Sh) were collected from different part of studied area, then their physical and mechanical characteristics were determined. In order to assessing the effect of freeze-thaw on physical and mechanical characteristics of sandstones, 60 cycles of freeze-thaw test was performed. Also in order to investigate the effect of salt crystallization on strength of studied sandstone, sodium sulphate crystallization test (100% weight solution of Na2SO4) was carried out in 20 cycles. Physical and mechanical characteristics of sandstones such as point load index, Brazilian tensile strength, wave velocity (Vp) and weight loss were computed after different cycles. To evaluate the effect of freeze-thaw and salt crystallization phenomena on durability of sandstones, slake durability test was conducted on specimens subjected to mentioned processes and changes occurred in slake durability index in 15 cycles were investigated. Based on results obtained from current study, it could be concluded that in comparison to freeze-thaw, salt crystallization can considerably reduce the strength and durability of sandstones and deteriorate them. Also it was found that index tests such as point load index, Brazilian tensile strength, wave velocity (Vp) and weight loss can predict the behavior of sandstones in different cycles of freeze-thaw and salt crystallization tests.

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