Effect of Relative Density and Particle Morphology on the Bearing Capacity and Collapse Mechanism of Strip Footings in Sand

This paper presents the results of a series of load tests performed on a half-strip model footing (width $B=50\mathrm{mm}$) placed on the surface of samples prepared with one of two uniform silica sands [Ohio Gold Frac (OGF) sand and Ottawa 20–30 (OTC) sand] with different relative densities. The sand samples were air-pluviated inside a half-cylindrical calibration chamber equipped with imaging capabilities. Sequential, high-resolution images taken during the model footing load tests were analyzed using the digital image correlation (DIC) technique to obtain the displacement and strain fields in the sand domain. The effect of sand relative density on the footing load–settlement curves and bearing capacity factor $N_{\gamma }$ was investigated for both OGF and OTC sands. The results obtained from the model footing load tests show that, for a given relative density, the bearing capacity of the footing and the value of $N_{\gamma }$ decrease with increasing roundness of the sand particles; the effect of particle roundness on the value of $N_{\gamma }$ is more pronounced for dense sand than for loose sand. Different points on the footing load–settlement curve were identified to investigate the development of the collapse mechanism of the model footing. Plots of the maximum shear strain contours were shown to adequately capture shear localization in the sand domain during model footing loading. The thickness of the shear band was found to be on the order of $10D_{50}$ and $7D_{50}$ for the model footing tested on dense OGF and OTC sand samples, respectively.