By C J Gravare, Goteborgs Betongpalar, G G Goble, Goble and Associates, Frank Rausche, University of Colorado and Garland Likins, Pile Dynamics
This paper was first publsihed in GE’s March 1980 issue
Piles are frequently the best solution to foundation problems. However, high safety factors are commonly employed to obtain a sufficient confidence leva’I in the foundation, given the uncertainties about hammer, soil and pile properties. By testing the integrity and bearing capacity of the pile, these uncertainties can be eliminated. This will give a more economical foundation design. Static load testing provides one method by which a pile’s integrity and bearing capacity can be verified. However, static load testing is time consuming and expensive, thus allowing for only a small number of tests on one site. To only a limited degree, therefore, can variability of soil, hammer and pile be taken into account by the static load test method.
Observations of ram stroke and pile set taken during pile driving have been used in a driving formula for quantitative analysis of ‘bearing capacity for at least the last century. Concurrent with the more recent development of automated computing capabilities for wave equation analyses”, electronic measurement techniques during pile driving were devised. Thus, the scope of pile driving observations dramatically widened and included accurate electronic measurements during the pile impact.
The Case method, named after Case Institute of Technology, Cleveland, Ohio, USA, consists of measuring pile top forces and accelerations. Field or laboratory processing then provides pile bearing capacity, pile stresses and hammer energies. In this article, the development of the Case method will be described. Its potentials will be discussed and an illustrative example will be given.