Abstract:
Deep foundation design has traditionally relied on conservative assumptions when subsurface information is limited, particularly for drilled shafts bearing on or socketed into rock. In many projects, standard geotechnical explorations consisting primarily of auger borings with limited or no rock coring can result in relatively conservative bearing pressures and larger-than-necessary drilled shaft diameters. Recent advancements in subsurface characterization and load testing techniques provide opportunities to reduce uncertainty in rock mass conditions and optimize foundation design.
This presentation examines how enhanced geotechnical exploration and load testing methods can improve the design and constructability of rock-socketed drilled shafts. The discussion begins with an overview of conventional design approaches and the limitations associated with typical exploration programs when evaluating drilled shafts bearing on shallow bedrock. The presentation then highlights how modern exploration techniques—including extended rock coring programs, detailed rock core classification, and geophysical borehole logging—can provide significantly improved characterization of bedrock conditions and structural discontinuities.
A case study involving heavily loaded building foundations is presented to demonstrate the impact of these enhanced investigation techniques. The project incorporated extensive rock coring, laboratory testing of rock strength, geophysical borehole logging, and bi-directional load testing to verify foundation performance. The improved characterization of the rock mass increased confidence in the allowable bearing capacity of the rock socket and enabled a substantial increase in design end bearing pressure. As a result, drilled shaft diameters and associated construction quantities were reduced while maintaining the required foundation performance.
The presentation also evaluates the economic implications of enhanced exploration and testing programs by comparing the upfront investigation costs with the resulting construction savings. Lessons learned from the project highlight how targeted subsurface investigations and load testing programs can reduce design uncertainty, improve contractor bidding confidence, and lead to more efficient deep foundation solutions. These findings illustrate how advancements in subsurface characterization and testing can support a more data-driven and performance-based approach to drilled shaft design.