The effects of sand grading on the bearing capacity of surface foundations

The bearing capacity of surface foundations in cohesionless soil has been studied extensively in the past decades. Experimental investigations have shown that particle size effects in the bearing capacity problem are associated not only with strength mobilization but also with the shear band thickness. Centrifuge testing can provide useful insights, especially when taking into consideration the scale effects, by using a modelling of models approach. This paper describes the results of a systematic study examining the effects of sand grading on the responses of surface footings. Four different sands, including two commercially sourced silica sands and two mixed silica sands, were deposited by air pluviation and tested under controlled conditions in the geotechnical centrifuge at Technical University of Denmark (DTU). To examine correlations often employed in the field between tip resistance (qc) of Cone Penetration Tests (CPTs) and footing bearing pressure (qf), a series of CPTs were conducted in samples prepared at similar conditions to the samples of the footing tests. The results indicate that the bearing capacity is controlled by a general shear failure mechanism and that further research is required to assess the range of applicability of direct relationships between bearing capacity and qc for surface footings