Experimental estimate of Nγ values and corresponding settlements for square footings on finite layer of sand

Abstract

Any structure constructed on the earth is supported by the underlying soil. Foundation is an interfacing element between superstructure and the underlying soil that transmits the loads supported by the foundation including its self weight. Foundation design requires evaluation of safe bearing capacity along with both immediate and long term settlements. Weak and compressible soils are subjected to problems related to bearing capacity and settlement. The conventional method of design of footing requires sufficient safety against failure and the settlement must be kept within the allowable limit. These requirements are dependent on the bearing capacity of soil. Thus, the estimation of load carrying capacity of footing is the most important step in the design of foundation. A number of theoretical approaches, in-situ tests and laboratory model tests are available to find out the bearing capacity of footings. The reliability of any theory can be demonstrated by comparing it with the experimental results. Results from laboratory model tests on square footings resting on sand are presented in this paper. The variation of bearing capacity of sand below a model plate footing of square shape with variation in size, depth and the effect of permissible settlement are evaluated. A steel tank of size <TEX>$900mm{\times}1200mm{\times}1000mm$</TEX> is used for conducting model tests. Bearing capacity factor <TEX>$N_{\gamma}$</TEX> is evaluated and is compared with Terzaghi, Meyerhof, Hansen and Vesic's <TEX>$N_{\gamma}$</TEX> values. From the experimental investigations it is found that, as the depth of sand cushion below the footing (<TEX>$D_{sc}$</TEX>) increases, ultimate bearing capacity and settlement values show an increasing trend up to a certain depth of sand cushion.