The bearing capacity of circular footings on sand with thin layer: An experimental study

Thin layers have substantial effects on the ultimate bearing capacity, despite their seeming insignificant. In this research, the effects of a thin layer on the ultimate bearing capacity of a circular footing on the sand bed are investigated by small-scale physical models. The investigations were carried out by varying the material type, thickness, and depth of the thin layer. The results indicate that the weak thin layer decreases both the ultimate bearing capacity and stiffness of the soil-footing system and the strong thin layer increases both the ultimate bearing capacity and the soil-footing system stiffness. The amount of this effect depends on the thickness, depth of deposition, and the material type of the thin layer. According to the results, the weak layer for the critical depth of 1B led to the most reduction in ultimate bearing capacity by 26% (from 183 kPa to 135 kPa), while no effects were observed at the depth of 2B. The strong layer is also for the state where this layer is just below the footing, had the highest increase in ultimate bearing capacity by 329% (from 183 kPa to 603 kPa), but at a depth of about 1.25B, it was ineffective.