Experimental Study of the Horizontal Thin Layer Effect on the Bearing Capacity of Circular Footings Resting on Sand

In general, despite their seeming insignificance, there are some details in the ground that have significant effects on soil-foundation system behavior such as slip surfaces, shear bands, and thin layers (Valor et al. 2017). Terzaghi (1929) termed “these features minor geologic details and pointed out their enormous potential effects on the safety of dams”. In the literature review very little study has been performed on the effects of a thin layer (Valor et al. 2017, Ziccarelli et al. 2017, Oda and Win, 1990)In the present paper, the influences of the horizontal thin layer on the ultimate bearing capacity of the circular foundation resting on the sandy bed were studied by implicating a small-scale physical model for the soil-foundation system. The problem of the soil- circular footing system is schematically illustrated in Fig. 1. The problem is investigated under the axisymmetric condition, and the circular foundation is rigid. This foundation rests on the ground surface, on the other hand, the initial depth of embedment is nil. The studies were performed by the material type, thickness, and depth of the thin layer variation. For the bed sand, crushed uniform silica sand (SP) with medium density was used. For the thin layer, materials with different strength properties (strong and weak) in comparison with the sandy bed were used.For the weak layer, the clay powder with CL classification was used. Clay with a natural moisture content of 5.5% and a very low density of 12.1 kN/m3 was used consistently in all of the experiments.For the strong layer, a fine-grained asphalt mixture with an unconfined compressive strength of 1460 kPa and unit weight19.12 kN/m3 was used.