The functions of cofferdams are defined, and their types are divided into two main classifications: the first constructed of soil, concrete or timber, and the second depending primarily on steel sheet piling. These are further sub-divided and listed in two charts. The choice available to the designer is discussed in relation to the permanent structure to be built within the dam, the site conditions,the depth of the cofferdam and the nature of the ground.
For design purposes cofferdamas re divided into two categories, namely singleskin and doubleskin, the latter including cellular cofferdams. The basic principles are discussed and attention is drawn to certain aspects of the design of cofferdams in both categories. Graphs for use in the preparation of preliminary designs and estimates for cofferdams of conventional construction are given.
Finally, the mechanisms of failure of cofferdams are reviewed. Reference is made to the fact that they are generally derived from the inability of the ground inside the cofferdam to withstand the external forceasn d not fromth e structural failure of the materials used in the construction.
