BEHAVIOUR OF RING FOOTINGS ON REINFORCED SAND UNDER VERTICAL AND LATERAL LOADS

Abstract

The ground improvement techniques are now sufficiently well developed to transform the weak soil into strata of desired strength and compressibility. The development of reinforced soil has provided Geotechnical Engineers a material, which can appropriately employed, and can offer substantial economy over conventional techniques. For costly structures such as high rise buildings, overhead tanks, sea ports and embankment construction, it is necessary to use artificially manufactured polymer reinforcing materials, which arc strung, non-degradable, temperature and chemical resistant. These materials include geotextiles, geogrids, geomembrances and geocommiles. There is growing need to develop design and construction techniques for use in regional soils. The present investigation has been carried out to study the behaviour of ring footings under central 'vertical loads and constant vertical and progressively increasing lateral load on dry sand reinforced with Tensar SS....20_geogrid. Three dimensional tests have been carried out on model footings with external diameter of 20 cm and ratio of internal diameter to external diameter of 0.0, 0.2, 0.4 and 0.6. In all experiments, model footings were placed on surface of sand bed. The values of constant vertical loads have been kept as 10 percent, 20 percent and 40 percent of the ultimate vertical load. Ratio of height of lateral load application to external diameter of footing have been kept as 0.5. For tests on reinforced sand, ratio of vertical spacing between reinforcement to external diameter of footing have been kept as 0.25. For central vertical load tests, length of reinforcement to external diameter of footing and number of reinforcement layers have been kept as 2,3 and 2,3,4 respectively. For constant vertical and progressively increasing ii lateral load tests length of reinforcement to external diameter of footing and number of reinforcement layers have been kept as 3 and 2,3 respectively. Tests were conducted on poorly graded dry_Amanathgarh_sand. Sand was deposited by rainfall technique to achieve a reproducible relative density of 68.85%. In all sixty four tests have been conducted, out of which four tests were conducted under central vertical load on unreinforced sand, twenty four tests were conducted under central vertical load on reinforced sand, twelve tests were conducted under constant vertical and progressively increasing lateral load on unreinforced sand and twenty four tests were conducted under constant vertical and progressively increasing lateral load on reinforced sand. The test data have been presented in the form of various plots. From the analysis of test data it has been concluded that (i) under central vertical load increase in the number of layers of reinforcement and increase in size of reinforcement has led to an increase in bearing capacity of soil and decrease it settlement, (ii) under central vertical load, bearing capacity ratio decreases as the annuli ratio 'n' increases, (iii) under constant vertical and progressively increasing lateral load. The lateral load capacity of ring footings on sand decreases with increase in annuli ratio 'n', (iv) For all values of 'n', the lateral load capacity of ring footings increases with increase in constant vertical load, (v) For same magnitude of lateral load, the lateral displacement and tilt decreases with increase in vertical load.