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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.

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Clay soils and their related abnormal behavior such as excessive shrinkage, swelling, consolidation settlement and cracking on drying has been the subject of many investigations. Previous studies mainly evaluated the effects of additives such as lime, cement and sand on these characteristics. Initial results indicated that the soil characteristics were improved. However, reportedly in many cases, these additives resulted in a decrease in plasticity and increase in hydraulic conductivity. As a result, there has been a growing interest in soil/fiber reinforcement. The present investigation has focused on the impact of short random fiber inclusion on consolidation settlement, swelling, hydraulic conductivity, shrinkage limit and the development of desiccation cracks in compacted clays. To examine the possible improvements in the soil characteristics, samples consisting of 75% kaolinite and 25% montmorillonite were reinforced with 1, 2, 4 and 8 percent fibers as dry weight of soil with 5, 10 and 15mm lengths. Results indicated that consolidation settlements and swelling of fiber reinforced samples reduced substantially whereas hydraulic conductivities increased slightly by increasing fiber content and length. Shrinkage limits also showed an increase with increasing fiber content and length. This meant that samples experienced much less volumetric changes due to desiccation, and the extent of crack formation was significantly reduced.

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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.

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In saturated soils, heating induces thermal expansion of both grains and the pore fluid. Lower thermal expansion coefficient of aggregates results in the increase of pore pressure and reduction of the effective stress besides subsequent volume changes due to the dissipation of pore pressure and heat transfer. Dissipation of thermally induced pore pressure with time is a coupled thermo-hydro-mechanical (THM) phenomenon, involving gradients of pore pressure and temperature, hydraulic and thermal flows within the mass of soil and changes in the mechanical properties with temperature. The objective of this paper is presentation of a numerical method to determine the effect of temperature on consolidation of clays. In this regard, the finite element code, PISA is used for one dimensional THM analysis of porous media. The analysis performed using both linear elastic and elastoplastic Cam clay models. Modified Cam clay model was applied in elastoplastic analysis. Variation of temperature, displacements and pore pressure determined with time and compared with numerical solutions of other researchers. Also it was indicated that implementation of coupled THM analysis yields better results for displacements compared to the hydro mechanical (HM) one. Application of elastoplastic constitutive model instead of linear elastic one indicated that preconsolidation pressure has an important effect on results of analysis.

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In this technical note, a methodology is introduced for reliability calculation of consolidation settlement based on cone penetration test (CPT) data. The present study considers inherent soil variability which influences consolidation settlements results. To proceed reliability analysis, the measured data of a sample corrected cone tip resistance (􀝍􀯧) is detrended using a quadratic trend and the residuals are assumed to be lognormally distributed random field. Realizations of 􀝍􀯧 is generated by using spatial variability of residuals including standard deviation and the scale of fluctuation. The quadratic trend and the generated residuals are then combined to correlate shear and bulk modulus as input consolidation properties for coupled analysis and subsequently consolidation settlement was calculated by using finite difference method adopted in Monte Carlo simulations. The results of reliability analysis are presented describing the range of possible settlements by considering characteristics of uncertainties involved at the particular site. Number of realizations rendering settlements smaller than the allowable settlement must be such that guarantee proper performance or acceptable reliability index.

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In this study, a researching program is conducted by cyclic triaxial test to determine the post-cyclic behavior of Bushehr carbonate sand retrieved from the north of the Persian Gulf, under anisotropic consolidation at 200 kPa confining pressure. The article compares the post-cyclic monotonic strength and excess pore water pressures generated after the test with the pre-cyclic monotonic results. The results attest to the existence of a relationship between CSR (Cyclic Stress Ratio) and the frequency of failure cycles. The article also investigates the relationship between the amount of excess pore pressures generated during both the cyclic and post-cyclic loading, revealing an increase in the post-cyclic strength and stiffness of sand retrieved from Bushehr. Also the effect of multi stages cyclic loading, density, pore pressure and stain history in post cyclic strength and stiffness is evaluated. The increasing in post cyclic strength and stiffness depends on excess pore pressure generated during cyclic loading and stain history. This article also reveals that a distinct trend in the relation between post cyclic behavior and crushing value does not exist at lower confining pressure.