The influence of foundation stiffness on the behaviour of surface strip foundations on sand

Abstract

The objective of this study was to determine whether the contact stress distribution underneath a strip footing on dense cohesionless sand can be predicted as a function of the properties of the footing and that of the underlying sand. Together, the footing and the underlying sand form a foundation system which can be classified in terms of relative stiffness. Centrifuge model tests were conducted on seven aluminium footings of various depths and hence stiffness, and one reinforced concrete footing, during which the qualitative variation in contact stress distribution underneath the footing was captured with the use of Tekscan™ pressure sensors. It was found that, as long as the relative stiffness of the foundation classifies as “stiff”, the contact stress distribution underneath the footing is approximately uniform. As the relative foundation stiffness is reduced, the contact stress underneath the footing edge as a percentage of the maximum stress occurring underneath the column, reduces. In the case of a semi-flexible footing tested, zero pressure was measured underneath the footing edge in response to loading of the footing. An expression is presented to allow the contact stress under the edge to be estimated as a function of the relative stiffness of the foundation. This allows the contact stress distribution underneath semi-stiff footings to be estimated. The stiffness of the model reinforced concrete footing tested reduced considerably due to cracking during loading. It is recommended that footings be provided with sufficient stiffness to classify as stiff. A modification of the benchmark value for the minimum relative stiffness classifying as stiff is proposed, based on the results of the centrifuge tests.