Deep Foundation Design When You Can’t Dig a Hole?

Drilling investigations are often not feasible in remote areas and sensitive environments. In these situations, significant risk is placed on the designer and construction when there is limited direct subsurface investigation. Near surface geophysical survey is standard practice to identify subsurface features but has not been utilized for deep foundation design or constructability. This paper demonstrates the use of near surface geophysics to design and address constructability for laterally loaded deep foundations, illustrating its limitations and requirements. As presented herein, shear wave velocities measured by near surface refraction microtremor methods correlate well with pressuremeter modulus measurements and density analysis. The modulus and density of subsurface materials control foundation performance and affect drillability. In this paper, the designs of laterally loaded deep foundations from shear wave velocity are compared with designs using blow count correlations and with designs using pressuremeter measurements. Shear wave velocity correlated to known subsurface conditions is useful for sizing drillings, estimating drilling rates, and evaluating tooling needs. Correlations are presented here for the use of shear wave velocities for designing and constructing laterally loaded deep foundations based on research conducted in central Arizona. The application of these correlations has the potential to reduce risk associated with building deep foundations in locations where direct subsurface sampling is not feasible.