This paper presents a series of laboratory tests and evaluates the effect of polypropylene fiber inclusion on volume change behavior and soil-water characteristics of expansive soils. Specimens were statically compacted at maximum Proctor dry density and optimum moisture content with 0%, 0.5% and 1% polypropylene fiber inclusions by dry weight of the soil, and their volume change behavior was studied through swell-shrinkage and consolidation tests. The soil-water characteristic behavior, which is the most significant aspect of soils, was also obtained by a series of matric suction measurements using filter paper technique. It was concluded that polypropylene fiber inclusion is very effective in reducing the compression and swell indices and swell pressures as well as onedimensional swell amount in saturated condition. Upon desiccation, shrinkage of reinforced soil reduced considerably, as the shrinkage limit increased by more than 50%. Therefore, fiber reinforcement can effectively reduce swell-shrink movement of expansive soils.

Beach sands are composed of a variety of minerals including quartz and different carbonate minerals. Seawater in beach sand contains several ions such as sodium, magnesium, calcium, chloride, sulfate, and potassium. These variations in mineralogy and the presence of salts in beach sand may affect the treatment via enzyme-induced carbonate precipitation (EICP). In this study, set test tube experiments were conducted to evaluate the precipitation kinetics and mineral phase of the precipitates in the presence of zero, five, and ten percent seawater (v/v). The kinetics were studied by measuring electrical conductivity (EC), pH, ammonium concentration, and carbonate precipitation mass in EICP solution at different time intervals. A beach sand was also treated using EICP solution containing zero and ten percent seawater at one, two, and three cycles of treatment. Unconfined compressive strength (UCS), carbonate content, and mineralogy of the precipitates in the treated specimens were evaluated. The kinetics study showed that the rate of urea hydrolysis and the rate of precipitation for zero, five, and ten percent seawater were similar within the first 16 h of the reaction. After 16 h, it was observed that the rates dropped in the solution containing seawater, which might be attributed to the faster decay rate of urease enzyme when seawater is present. All the precipitates from the test tube experiments contained calcite and vaterite, with an increase in vaterite content by increasing the amount of seawater. The presence of ten percent seawater was found to not significantly affect the UCS, carbonate content, and mineralogy of the precipitates of the treated beach sand.

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Sand-Na-bentonite mixture is widely used as engineering barrier material which usually possesses hydraulic conductivity below the regulatory limit (10 -7 cm/s). However, in some areas natural Na-bentonite is not easily available, instead an abundantly prevailing local expansive soil can be an alternative. This study assesses the suitability of a local expansive soil mixed with zeolite, readily obtained from natural reserves in Turkey, to be proposed as a landfill liner in a semi-arid climate. The choice of zeolite is due to its already well understood high adsorption capacity for heavy metals as well as its pozzolanicity. The volume change, strength, and hydraulic conductivity characteristics were studied with the effect of durability through ageing. When expansive soil to zeolite ratio of 0.5 was used, the results indicated improved properties with curing. Swell potential was observed to decrease by 85% within 90-day curing period, while 30-34% reduction was noted in shrinkage and compressibility characteristics. The hydraulic conductivity was observed to remain below the regulatory limit under all confining pressure ranges studied, provided the curing time was at least 90 days.Moreover, the mixture attained improved strength characteristics with time, and proved to be sustainable over the period studied. Therefore, it was concluded that expansive soil mixed with zeolite could be a good alternative to sand-Na-bentonite, mainly in developing areas of growing population and environmental degradation.

Posidonia oceanica (PO) is the most plentiful seaweed of the Mediterranean Sea, which grows all along the coastal areas, forming widespread meadows. The leaf rejuvenation process of Posidonia oceanica typically occurs in fall when an increase in wave action causes the dead seaweeds to be transported and usually piled up along the coastal areas. This paper investigates the effect of PO ash stabilization on behaviour of an expansive clay. The ash was obtained by combustion of crushed PO pieces in a muffle furnace at 550 C. Atterberg limits, linear shrinkage, particle size distribution, one-dimensional swell, and unconfined compression tests have been carried out on natural soil as well as soil mixtures with 5% and 10% PO ash. There has been no significant improvement in the soil properties with 5% ash inclusion, whereas 10% ash has noticeably reduced the swell amount and increased the compressive strength. It is therefore concluded that there is a potential for the use of PO ash in geotechnical engineering applications.