The Impact of Using Recycled Plastic Fibres on the Geotechnical Properties of Soft Iraqi Soils

Soft clay may experience uncontrollable settlement and loss of critical bearing capacity due to the fact that clayey soils possess remarkable plasticity which increases moisture retention and causes decreases in strength, volume changes, and loss of compressive strength. Thus, these types of soils need to be improved before use in construction. A huge volume of waste results from daily human life, which leads to disposal problems and causes environmental contamination and health risks; thus, the usage of such industrial wastes as supporting construction materials could effectively contribute to environmental preservation and minimisation of these harmful effects. In this work, plastic fibre was used as the additive for the soft clayey soils of Baghdad, using different percentage concentrations of 1, 2 and 4% (the proportion of stabilising matter to soil net weight) of the dried soil. This work studied the properties of clayey soil with and without the additives. The studied soil properties were grain size distribution, Atterberg limits, unconfined compressive strength, compressibility, and California bearing ratio. From the laboratory tests results, the effect of plastic fibre content had a remarkable effect on the liquid content, plastic behaviours, and plasticity index. The liquid limits decrease as the percentage of plastic fibre increases while the plastic limit increases, this causes a great reduction in plasticity index. This decrement approached 50% with the addition of 4% plastic fibre to the clayey soil. Inclusion of different percentages of plastic fibre led to noticeable reductions in maximum dry unit weight up to approximately 11% by adding 4% plastic fibre, while the optimum moisture content reduction approached 7.5%. The effect of plastic fibre was also clearly shown on the unconfined compressive strength of soils; the increase in the unconfined compressive strength approached 180% with the addition of 4% plastic fibre. The ratio of compression index (cc) to recompression index (cr) reduced as the percentage of plastic fibre increased up to 2%, although it increased after this point. Finally, the California Bearing Ratio (CBR) increased as the plastic fibre content increased, with this increment approaching 210 % when adding 4% plastic fibre.