Assessment and Reuse of Old Foundations

Abstract

Little is known about the foundations beneath many historic buildings and bridges. For rehabilitation projects, it is important to know the nature of the foundation system and its condition. In replacement projects, cost savings and sometimes environmental benefits can be gained from the reuse of existing foundations in new structures. In large cities, almost any new construction involves the demolition of a previous structure, which poses the problem of what to do with the old foundations. Many are too deep to be removed economically, and some are almost certain to be in the way of proposed new foundations. It is therefore a great advantage if they can be incorporated into the new design, but to do this, the engineer must have accurate information about the foundation type and depth to estimate load-bearing capacity. The authors have worked on a number of projects in the last few years that have included increasing the load on or reusing existing foundations. Information about foundation type and depth has been gained from the use of specialized nondestructive tests. In many cases, the authors also had access to archive information that included soil borings in the vicinity to correlate with test data. The methods used to assess existing foundations and allow their inclusion in the design of new foundation systems are discussed, and case histories are given for concrete drilled shafts, timber piles, and steel sheet piles.