BEHAVIOUR OF FOOTINGS ON SAN REINFORCED WITH GEOSYNTHETICS

Abstract

The need to improve the bearin capacity and settlement characteristics of soils has led to the introduction of the concept of reinforced earth. A wide range of materials, both natural and manufactured ones, are available for use as soil reinforcement. Geogrids, a group under geosynthetics family form one such artificially manufactured materials, that are strong, nonbiodegradable, temperature resistant and chemical resistant. There is a growing need to develop the design and construction technique for these materials for use in regional soils. The present investigation deals with the laboratory studies on the behaviour of a square (20 cm x 20 cm) footing resting on a deep, homogeneous, medium-dense sand bed reinforced with geogrid mats. The parameters chosen for investigation are: the depth of the top layer of reinforcement below the base of the footing, the number of. layers of reinforcement,and the placement of the footing with respect to the ground level. Locally available Amanathgarh sand graded as SP according to IS 1498-1970 was used. Sand was deposited by rainfall technique to achieve a reproducible relative density of 60 per cent. The depth of the top layer of reinforcement below the base of the footing was taken as 0.25 B, 0.50 B and 0.75 B for each value of N, the number of reinforcement layers. iii The number of layers of reinforcement used were 1, 2 and 3., • The tests were performed for bOth surface footing (Dent)) and embedded footing CDem0.5 B3. On the basis of the load settlement diagrams obtained from the test data, certain conclusions have been drawn. It was observed that there is an optimum depth below the base of the footing. The first layer of reinforcement, when placed at this position, would result in a maximum mobilisation of its tensile strength. Increase in the number of- layers of reinforcement has led to an increase in the bearing capacity of the soil and decrease in settlement. The placement of footing has been observed to have a significant influence on the optimum depth of first layer of reinforcement, and also on the bearing capacity and settlement characteristics.