Enhanced in Situ Geotechnical Testing for Bridge Foundation Analysis

Geotechnical analyses of bridge foundations are complex because of the difficulties in addressing the highly nonlinear and anisotropic stress-strain-strength-time behavior of soils, from the nondestructive small-strain range region through to failure conditions. Often engineering practice overrelies on a single test value from soil borings [the standard penetration test (SPT) N-value] for the evaluation of all necessary geotechnical parameters, which is unrealistic. There exists, in fact, a variety of in situ measurement devices for the better definition of soil engineering properties, particularly hybrid devices such as the seismic piezocone and seismic flat dilatometer, as related to foundation applications. The importance of small-strain field stiffness measurements (i.e., shear wave velocity) is discussed and illustrated with two case studies involving the axial response of drilled shaft and driven pile foundations. The examples are reviewed within the context of elastic continuum theory but may be applied similarly for use in site-specific determinations of nonlinear spring constants and well-known t-z, p-y, or q-z curves, or all three.