The Actual Factor of Safety in Foundations

IN determining which branch of structural engineering should be treated in this paper, cognisance was taken of the fact that during the last few months, several requests have been made for information regarding roof trusses which have been fabricated and erected by means of welding. It seemed, therefore, that the subject would be of sufficient interest to members to be given here, especially as the introduction to welded construction might be made more easily by way of welding roof trusses, and by incorporating them into other forms of construction until experience of the process has been gained, when further portions or the whole structure, could be undertaken with confidence. C. Helsby

THE subject of this paper may be considered somewhat out of the ordinary for discussion by the members of the Institution of Structural Engineers. As, however it has an important bearing on the preparation of the foundations which support the structures designed and built by the members of this Institution, it will be seen that it is a matter of primary importance. Without the use of compressed air it is sometimes impossible to reach a sound foundation by ordinary excavation methods, or even by piling. The foundations of bridges crossing wide rivers and estuaries in deep water are generally built in caissons sunk under compressed air. Subaqueous tunnels in water-bearing strata are driven by shields with the aid of compressed air to balance the water pressure, and many harbour works are built by divers or by diving bells. Sir Henry Japp