A comparison of the bearing capacity of flat and conical circular foundations on sand

T. Orr, Trinity College Dublin, Ireland The authors have presented an interesting paper concerning a fundamental problem for geotechnical engineers: the bearing capacity of circular foundations on sand. In this paper the authors have included an equation for the factor Na in the bearing capacity equation for circular foundations on the ground surface, which has been determined from the results of centrifuge tests. The authors’ paper is particularly relevant at this time as the new European Standard for Geotechnical Design, EN 1997-1: Eurocode 7 Geotechnical Design (CEN, 2004) is due to be implemented in March 2010 by the national standards organisations in the member countries of the Comité Européen de Normalisation (CEN). EN 1997-1 provides the principles for geotechnical design as code text and some calculation models in informative annexes, that is not as mandatory code text. One of these calculation models is an analytical method for calculating the bearing capacity of a spread foundation. As no exact solution exists for Na, a number of equations have been proposed for Na since the bearing capacity equation was first introduced by Terzaghi (1943). The equation in EN 1997-1 for Na for a strip foundation with a rough base is