Alternative Design Approach Addressing High Shear Demands in Rock Sockets

It is a common strategy to “socket” drilled shafts into rock to develop lateral or axial capacity where overburden soils are shallow and/or relatively weak compared with the underlying rock formation. Methods of numerically modeling soil-structure interaction using discrete, nonlinear springs representing soil response as a function of pile discplacement (p-y methods) demonstrate shear forces near the top of the rock sockets that are significantly larger than the applied forces to the drilled shaft. The amplification effect has been shown to decrease with decreasing rock quality. The ensuing shear forces can often significantly exceed the structural capacity of rock sockets as calculated using traditional sectional methods with practical reinforcing ratios. Considering the mechanics and geometric characteristics of load transfer through the rock socket into the supporting geomaterial, it is apparent these elements should be characterized as D-regions for which an STM approach is an appropriate tool for assessing the rock socket structural capacity. Such an approach has been demonstrated to yield drilled shaft and rock socket sections that are more economical and constructable.