SETTLEMENT OF FOOTINGS ON CAPILLARY SAND BEDS

Abstract

The capillarity in sand and silty sand beds influence the load settlement behaviour of field load test plates significantly. This fact, if not appreciated in interpreting the results of load test may lead to estimation of allowable soil pressure on the unsafe side. Therefore in this dissertation an attempt is made to investigate the mechanism of capillarity in soils, its effect on the compressability and strength properties of soils and on the load-settlement behaviour of test plates and footings. The modes of occurrence of water in the soil, the capillary phenomena in the soil, the various zones of capillarity and the possible heights of capillary zone and its determination are discussed. In order to examine the effect of capillarity on load settlement behaviour, tests on 30cm x 30cm plate resting on capillary beds have been carried out. The results of these tests and the results of some tests on, 12 cm diameter, circular plate resting on capillary beds, carried out as a part of UGC career award scheme are presented and discussed. In order to suggest a suitable analytical procedure some of the methods of settlement computations are examined and a method which accounts for the increase in stiffness due to the capil-larity is adopted to predict analytically the load settlement behaviour of test plates resting on capillary bed. Results-ob-tained based on this analytical procedure and those obtained experimentally are compared. The results of the above analytical and experimental investiga-tions suggest that there is certain amount of cohesion with in the capillary zone, which should be taken into account in pre-dicting the behaviour of test plate/footing resting on capillary beds. It is also found that the capillarity reduces settlement significantly for an applied load intensity and enhances bearing capacity substantially.