Strengthening soil with natural and synthetic fibres: insights from full-scale plate load tests

Mechanical stabilisation, chemical stabilisation, and the use of geosynthetics are the evolved methods to overcome the limitations of black cotton soil. However, fibre reinforcement has the distinct advantages over the other methods. The objective was to study the effect of coconut coir and polypropylene fibres on the bearing capacity of black cotton soil, and to find the optimum dose. Thirty-four unconfined compressive strength tests were performed on soil reinforced with 0, 0.2%, 0.4%, 0.6%, 0.8%, and 1.0% of coconut coir and 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, and 0.6% of polypropylene, randomly distributed fibres, on a weight basis, with the aspect ratios of 80, 100, and 120. The optimum dose observed was 0.8% and 0.4% reinforcement of coir and polypropylene, respectively, with an aspect ratio of 100. The plate load tests were conducted on the unreinforced and optimally reinforced soil. The ultimate load obtained was 40, 77, and 97 kN for unreinforced, coir-reinforced, and polypropylene-reinforced soil, respectively. The outcomes of the study support the use of coir-reinforced soil for temporary structures and polypropylene-reinforced soil for permanent structures.