Photoelastic Analysis of a Cofferdam

Elastic stresses inside the soil mass of a cofferdam are determined using photoelastic technique. A cofferdam model was fabricated simulating the soil mass with gelatin and the steel sheet piles with urethane rubber. This model was tested in a state of plain strain, and, from the photoelastic data, elastic stresses within the fill material were found due to both gravity loading and water pressure. In the gravity loading case, normal stresses agree with the standard theory of soil mechanics for geostatic stresses. Water pressure introducing bending is found to affect the stresses appreciably causing a nonlinear distribution of stresses and pressure on the base of the cofferdam. Contrary to many theories, shear stresses are found to be higher near the sheet pile walls than the midplane. New failure surfaces, in accordance with the elastic stress state, are postulated.