Bearing capacity of trip footing on sand

Abstract

A study on the behavior of a centrally loaded artificially prepared air dry sand layer is thesis. The study is concerned with the apparatus to study the bearing capacity constituted of selected sands of Bangladesh. strip footing reported in development of sand on an this of an layers A bearing capacity testing apparatus was designed and constructed in the laboratory. The apparatus mainly consist of a model tank of dimensions 57 cm x 85.5 cm x 60 cm, a sand spreader, a levelling apparatus, a strip footing and a loading rig having a capacity of 27 kN. Plane strain model tests were carried out using a rough based footing resting on dense, (Dr = 80%to92%), semi-infinite (H/B~3) layer of sand collected from different locations of Bangladesh. The mechanical sand spreader was used to form the sand bed. Strain controlled'loads were applied and the plane strain conditions were carefully maintained. The bearing capacity tests were carried out for surface (D/B=O) and shallow (D/B=0.5,1.0) depth footing using four selected soil samples having different angle of internal friction. The load, settlement and rotation measurement were taken using load and strain dial gauges. Basic computer programs were developed to analyze the data and present the results. The effects of angle of internal friction(~) and depth of surcharge on bearing capacity, angle of internal friction on bearing capacity factors Ny, Nq and Nyq are studied. The results are compared with those predicted by the existing methods. It is observed that for a surface strip footing the bearing capacity results are in good agreement with that given by the empirical relation of Feda (1961) and Abdul Baki and Beik (1970) whereas for a shallow depth footing the results are in satisfactory agreement (Varying from 68% to 102%) with the results of Abdul Baki and Beik (1970). It is further noticed that when the footing depth closes to the width of footing the bearing capacity predicted by Terzaghi has excellent agreement (within a range of 90% to 95%) with the experimental results particularly for higher values of ~.It is, however, observed that,in general,the predicted results are on the safe side in almost all the cases. The experimental results show that the predicted values of Ny by existing formulas are highly conservative,the exception being that of Feda (1961), which is on the unsafe side. Terzaghi's (1943) formula predicts bearing capacity factor for surcharge,Nq, very closely while D/B is approximately 0.5. The reasonable agreement for Nq was also observed while using the formulas of Meyerhof (1955) and Br. Hansen (1961). Statistical analysis of the experimental results yield good correlations between ~ and the bearing capacity factors. And as such, these relations are proposed to estimate the bearing capacity of strip footing resting on Bangladesh sands.