Evaluation of strength chacteristics of coconut coir mat reinforced lithomargic clay

Lithomargic clay is a commonly found below Laterite soil throughout the Konkan belt of South India. Being a soft soil, it is very problematic to work with; showing high strength in dry conditions but suffering a significant fall in strength under wet circumstances. A heavy rainfall condition in the Konkan belt makes the area highly prone to erosion, landslides and slope failures. Thus, this study aims to strengthen the available soil by using coconut coir mats as reinforcement. The strength characteristics of the soil reinforced with the coir mats at different positions were studied, by conducting direct shear and unconfined compressive strength tests, to attain ideal reinforcement positioning. Cashew Nut Shell Liquid Oil (CNSL), a commonly used industrial disinfectant was used to improve durability and attain better strength characteristics. It was observed that both the proposed reinforcements, i.e. coir mats and coir mats coated in CNSL oil increased the strength of the clay. With untreated coir mats as reinforcement, an increase of 88% was attained in the compressive strength with the mats positioned at one third from both the ends of the mould, parallel to the base and a tenfold increase in the cohesion of the soil when the mats were placed in three layers i.e. one third from both ends and the centre vertical to the plane of shear. A further increase of 1.76% and 6.92% was achieved in the compressive strength and the cohesion value respectively when the coir mats were coated with CNSL oil.