Strength and permeability of sand-bentonite mixtures are of main concern, particularly in liner design. This study presents the results obtained from an experimental investigation of strength and permittivity of compacted sand-bentonite mixtures in the presence of water-reducing admixture of lignosulfonate. For this, sand-bentonite mixtures containing 4, 8, 12, 16% of bentonite were subjected to standard Proctor tests, to obtain the optimum water content and maximum void ratio of the mixtures. Similar specimens were prepared by partially replacing 0.5, 1 and 2% of water in the mixture with lignosulfonate. Additional specimens containing 16% of bentonite were prepared with 5% deviation towards the wet and dry sides of optimum water content, which was partially replaced with lignosulfonate for evaluation of the effects of deviation from optimum moisture content during densification. It was observed that partial replacement of water with lignosulfonate slightly increases the strength and decreases the permittivity, and that this effect was more pronounced as the replacement level was increased. Additionally, test results reveal that lignosulfonate replacement was more effective on the dry side of optimum water content.

It is a well-identified fact that more elaborate laboratory studies should be carried out for evaluation of dynamic properties of different types of soils. Regardless of the mechanisms affecting the mechanical behaviour of the soils, past studies reveal that existence of fiber positively affects the strength of either cohesive or non-cohesive soils. A short literature survey provides numerous studies on the stress-strain behaviour of fine/coarse soils, reinforced by polypropylene fiber. On the other hand, studies concerning fiber reinforced soils subjected to dynamic loading are relatively rare. Therefore, in this research it was intended to investigate the effects of polypropylene fiber inclusion on the dynamic behavior of a clayey sand soil, within an experimental framework. In this scope, a number of cyclic triaxial compression tests were conducted to assess the effect of fiber presence. The effects of fiber length and content were experimentally evaluated. Hence, the variation of shear modulus ratio and damping ratio values by shear deformation was plotted to observe the effects of fiber length and inclusion level as well. The results are presented along with detailed evaluations.

No abstract

In construction of landfills, embankments and transportation structures, use of clay-sand mixtures are commonly preferred. To provide stability and enhance engineering properties, stabilization with chemical admixtures is a reasonable approach. Unfortunately, freeze-thaw effect is a significant problem controlling the mechanical behavior of soils in cold regions. Since past studies on strength behavior of clay-sand mixtures stabilized using fly ash or cement exposed to freeze-thaw action is limited, in this study, an experimental framework was used to investigate the effects of clay content, admixture type, number of freeze-thaw cycles on strength of clay-sand mixtures including pozzolanic cement or class C fly ash. Sand specimens including 4, 8, 12 and 16% bentonite by weight were stabilized with 3, 6, 9 % pozzolanic cement and 5, 10, 15 and 20 % class C fly ash by weight, specimens were prepared at optimum water content of mixtures. The specimens were then subjected to 1, 3 and 10 freeze-thaw cycles after 28 days of curing period. Freeze-thaw resistance of specimens was determined by carrying out unconfined compression tests. Experimental results revealed that, under certain curing conditions, cement and fly ash stabilization positively affects the strength of sand-bentonite mixtures and dominates the negative effects of freeze-thaw action. As expected, specimens stabilized with pozzolanic cement provided higher freeze-thaw resistance compared to those amended with fly ash. Besides, analysis of secant modulus values revealed that, cement stabilized specimens showed a more rigid behavior after freeze-thaw action.

Site response analyses and solution of dynamic soil-structure interaction problems need determination of variation of shear modulus and damping ratio with shear strain. Since many studies in literature concern evaluation of behavior of sands and silty sands, a series of cyclic triaxial tests were performed to determine the variation of shear modulus and damping ratio of a nonplastic silt with shear strain. Stress controlled cyclic triaxial tests on silt specimens of initial relative densities ranging among 30%, 50% and 70% were performed. Tests were carried out on identical samples under different CSR levels, and the confining pressure was selected as 100 kPa. Variation of shear modulus and damping ratio of silts with cyclic stress ratio amplitude, relative density and number of cycles were investigated. It was understood that soil relative density and cyclic stress ratio amplitude has a significant influence on shear modulus and damping ratio of silts. It was also observed that, as the cyclic stress ratio amplitude is increased, greater shear modulus and lower damping ratio values were obtained.