Behaviour of Square Footing on Cement Modified Fibre Reinforced Sand Layer Underlain by Soft Clayey Soil

Deep foundations are generally suggested when soil at the site is weak soft clayey soil. The cost of construction of deep foundations like piles and piers is generally very expensive. However, bearing capacity of weak foundation soil can be improved by various soil stabilization methods so that it becomes suitable for shallow foundation. In present investigation, a layer of sand modified with 5% cement and reinforced with 0.75% polypropylene fibre was placed on top of soft clayey soil. Optimum percentage of cement and fibre required was first determined from proctor compaction tests and direct shear tests. Three different percentages of cement as 2, 3.5 and 5% and four different percentages of fibre as 0.25, 0.5, 0.75 and 1% were used for the study. Laboratory modelling was carried out on steel tank with square concrete block of size 20 cm × 20 cm and thickness 4 cm used as footing. Loads were applied by hydraulic jack and recorded in proving ring. Two dial gauges were used in diagonally opposite direction to measure settlement. Load-settlement behaviour of footing was studied by varying the ratio of thickness of top sand layer (H) to the width of footing (B) (as H/B = 0, 0.5, 1, 1.5 and 2) for both unreinforced and cement modified fibre reinforced sand layer underlain by soft clay. Optimum H/B ratio for cement modified fibre reinforced sand layer was found to be 1. However, for unreinforced sand layer, the H/B ratio was found to be significantly higher.