Failure of the St. Francis Dam

All reports as well as the press comments agree in the one outstanding conclusion that the failure was due to the foundation. There is, however, great diversity of opinion as to the principal delinquency of the foundation, and as to how it reacted upon the dam structure so as to produce initial failure. Moreover, some engineers of the highest standing attribute the disaster to the dam itself, its relatively weak concrete, its lack of water-tightness, the omission of contraction joints in first construction and the absence of a deep cut-off wall and of an efficient drainage system. Those who lay the blame on the foundation differ as to whether it was the saturation of the conglomerate, or the penetration of reservoir water in the parallel seams of the schist, or an upward slip of the conglomerate along the contact plane which was mainly responsible. With such lack of unanimity, it is evident that definite assurance on the part of any one is not helpful and that the problem must be treated with an open mind, regardless of previously held opinions. The following discussion is offered in an effort to reduce to some extent the field of speculation and controversy. The dam was built as a monolith of concrete which, when tested for crushing in 3-inch cubes gave a strength after three years of from 2200 to 1300 pounds. Such concrete cannot resist the tension which sets up on gradual dissipation of internal chemical heat, and numerous contraction cracks must have formed in the dam along planes of least resistance that is approaching the vertical and radial in the valley portion of the dam and inclined and radial in the abutments.