The fundamental purpose of this thesis is to employ the plastic theory in the design of a hypothetical steel sheet pile cofferdarm. Prior to undertaking this work, the author had had no previous experience with the plastic theory. Therefore, a portion of this thesis is devoted to the development of the fundamentals necessary for the actual design computations.

The theory of plastic analysis has been used as far back as the 1920's in Hungary for the structural design of apartment buildings. It is, however, only in recent years that the theory has been utilized to a significant degree in this country. Much progress has been made by J. F. Baker at Cambridge University, England and recently Lehigh University has been conducting many large scale tests of structural members and frames. It is primarily through these endeavors that the use of the plastic theory is being stimulated in the United States.

Very little work has been done to date in the application of the plastic theory to structures subjected to soil pressures, It seems, however, that structures such as designed in this thesis are ideally suited to be designed by the plastic theory.

The temporary nature of a cofferdam justifies the concept of designing for an ultimate load--deflections not being a consideration. Since the soil pressures are assumed to be triangular, there is very little possibility that the pressures would be greater than those assumed. It is, therefore, logical to design for the ultimate capacity of the structure, Nevertheless, a load factor is used to insure additional safety.

A solution to the problem of sheet pile penetration is presented in this thesis. As far as it is known, this is a new solution to the problem and would seem to be a significant contribution to the application of the plastic theory.