Stability of Cellular Cofferdams Against Vertical Shear

The concept of failure of cellular cofferdams by sliding along vertical planes (vertical shear) is examined in detail. The Terzaghi and Krynine approaches to evaluating stability against vertical shear lead to conclusions that are shown to be contrary to engineering expectations and philosophically difficult to accept. No reasonable failure mechanism that permits sliding along vertical planes is uncovered in the examination. It is suggested that if a measure of stability against failure by vertical shear is desired then the cellular cofferdam should be assumed to fail in simple shear. Failure by simple shear implies a near-vertical faliure surface and a ratio of horizontal to vertical stress of unity. However, it is also suggested that it may be better to ignore vertical shear entirely and to validate, with a view to adopting, design procedures proposed by Hasen.