Bearing capacity of a sand bed overlying a ingle layer of jute cloth

Abstract

This study deals with the behaviour of reinforced sand beds in relation to bearing capacity of footing foundation resting on these. The sand beds consist of layer of sands of varying thickness,with horizontally placed jute cloth reinforcement inclusion. Model tests were conducted to investigate the bearing capacity, settlement and rotation of rough based strip, square and circular footings. Tests were carried out in a tank on beds of sand having relative densities varying from 73 to 88 percent. The triaxial angle of internal friction of the sand was approximately in the range of 34° to 390. The sand bed thickness was maintained to three times the least dimension of the footing. Strain controlled vertical loads were applied on the footing placed on the surface of sand bed. The effects of angle of internal friction of sand and the depth of reinforcement, on bearing capacity are studied. The results are established, discussed and compared with those predicted by the existing methods. It is observed that bearing capacity factors predicted by Terzaghi (1943), Meyerhof (1963), Hansen (1970) and Vesic (1973) are all conservative even if the plane strain angle of shearing resistance is considered in estimating the bearing capacity. The variation is within 32 per cent to 62 percent of the experimental results. The observed ultimate bearing capacity shows reasonable agreement with the predicted value given by Feda (1961), Abdul Baki and Beik (1970)_ and Quadir (1990). Statistical analysis of the experimental results yield good correlations between ~ and the bearing capacity factors. As such, these relations are proposed to estimate the bearing capacity of strip footing resting on Bangladeshi sands. The results also indicate that shape factors for square and circular footings vary with the angle of internal friction of soil. In general, shape factors found to have larger values than those suggested by Terzaghi (1943). The observed values of shape factors, for foundations in dense sand (~ = 39.2o)are found to agree with values predicted by Terzaghi (1943). For the case of reinforced sand bed, it is observed that the bearing capacity of the sand layer increases significantly while compared to an unreinforced bed. This is also found to be true if a particular settlement is considered for a comparison of bearing pressure. This increase of bearing capacity is found to be in the range of 160 percent to 270 percent. The reinforcement depth in the foundation sand bed has also a significant influence on bearing capacity. In general, the bearing capacity increases with the decrease of top layer thickness. The experimental values of bearing capacity are found to have good agreement with the predicted values of Binquet and Lee (1975b). For unreinforced bed, failure outcrop arises on all sides. It is at a distance of 2B to 3B from the edges of the footing. Nearly circular failure outcrop arises when the bed was loaded with circular footing. Failure of reinforced bed was either by tie pullout after overcoming frictional resistance or by shear failure above the reinforcement.