Geotechnical Resistances of Drilled Shafts in Triassic Basin Sedimentary Rocks

Load tests on drilled shaft foundations with rock sockets in sedimentary formations associated with various Triassic Basins in the Mid-Atlantic region show that some generalizations are possible for estimating geotechnical resistances. Axial load tests on drilled shafts in locations several hundred miles apart produce surprisingly similar results. The common feature is the geology: all of the load-tested rock sockets considered were constructed in sedimentary rock associated with one of the rift basins that developed in response to breaking apart of the supercontinent Pangaea that began during the late Triassic Period (about 220 million years ago) and coincided with opening of the Atlantic Ocean. More specifically, all of the tested rock sockets were in the ‘red bed’ facies of the rift basin sediments consisting of reddish-brown siltstone, sandstone, and shale. Each of the projects described herein and the associated load tests are described and used to illustrate fundamental principles of rock socket design and how load testing can be used as a design tool. The important role of quality construction, in combination with quality assurance through inspection and testing, is emphasized, especially as it relates to the evaluation of base resistance for rock socket design.