Photoelastic Determination of Contact Stresses of Foundations

The contact stress distribution underneath foundations under operating loads is important for a realistic estimation of settlements. Theoretical and numerical models are difficult to apply due to the nonlinear properties of the subsoil. Previously conducted modeland full-scale tests on real sand gave varying and contradictory stress distributions. A series of model tests using a photoelastic model of a rigid foundation resting on sand were conducted at Queen's University Belfast, Northern Ireland, to determine contact stresses underneath a rigid foundation. Models were tested for centrally and eccentrically applied loads at different load levels. It was found that the stress distribution for central loading was bell shaped, with zero corner stresses for small and nonzero contact stresses for higher loads. For eccentrically loaded foundations, the stress distribution was again bell shaped, whereby the effective width of the foundation was reduced. The photoelastic method was found a valuable tool for analyzing this nonlinear contact problem.