Undrained Strength Characteristics of Fibre Reinforced Expansive Soils

Expansive soils are those whose volume changes take place while it comes in contact with water. It expands during rainy season due to intake of water and shrinks during summer season. Expansive soils owe their characteristics due to the presence of swelling clay minerals. Expansive soils cover nearly 20% of landmass in India and include almost the entire Deccan plateau, western Madhya Pradesh, parts of Gujarat, Uttar Pradesh, Andhra Pradesh, Karnataka and Maharashtra. The properties that describe the expansive behaviour of soils are free swell index, swell potential and swell pressure. This behaviour has an impounding effect on the bearing capacity and strength of foundation lying on such a soil. Some of the stabilization techniques which are currently being used are physical alternations, sand cushioning, belled piers, under reamed piers, granular pile anchors, chemical stabilization, and fibre reinforcement techniques. This paper focuses on improvement in the strength characteristics of stabilized Chittur soil. The commonly used stabilizer for expansive soils is lime. This paper looks upon alternative materials such as fly ash and polypropylene fibres in order to reduce the lime content. It was concluded from the trials that an optimum combination of 1.5% lime, 10% fly ash and 0.2% polypropylene fibres contribute to a 200% increase in the unconfined compressive strength of the Chittur soil.