WES Theoretical Manual, Part I: Introduction

The manual opens by explaining how a filled cell actually behaves. A good picture is a thin plastic bag filled with sand: push on it, and the only resistance comes from the shear strength of the sand. A sand-filled metal can is the wrong picture, because the can carries the load in its shell. A real cell lies between the two, but much closer to the bag.

It then reviews the history. The first steel sheet pile cellular cofferdam went up at Black Rock Harbor near Buffalo in 1908, and until Terzaghi's 1945 paper most cells were designed as gravity walls. Terzaghi pointed out the error, introduced the idea of checking shear on a vertical plane in the fill, and raised the possibilities of slip between fill and sheeting and of the inboard wall plunging into the foundation. Hansen, Ovesen, and Cummings proposed other failure modes, and notable cofferdam failures from underseepage and weak foundations added more.

Part I also explains the simplifications every analysis rests on, such as using an average vertical slice and an equivalent cofferdam, and where those simplifications are questionable. Read it first, because it tells you which of the later checks deserve the most confidence.