Improved design for drilled shafts in rock

Drilled shafts are the foundation of choice for bridges where rock lies near the ground surface and when large loads have to be transferred to the ground. In such cases sockets are excavated into (or onto) the rock, and the sockets are concreted. The "rock socket" provides resistance to load through a combination of side and base resistance. However, excavation of drilled shafts in rock is time consuming and expensive relative to excavation of soil, which is an impediment to rapid construction. One such issue in construction of rock sockets is the identification of the top of a rock stratum when drilling through overburden using drilling slurry.;The major objective of this project was to improve the current TxDOT design method for drilled shafts socketed in rocks and identify the important parameters influencing the side and base resistance for variety of rock types. The parameters investigated were rock types and joints, drilling tools, and quality of construction. The verification was achieved with high-capacity load testing of rock sockets at selected sites, together with special borehole profiling and normal geotechnical testing of the rock. At one site, the rock socket was load-tested in conjunction with the overburden soil above it in order to address the issue of adding frictional resistance from overburden soil to the capacity of the rock socket. The information obtained in the field testing program was extended to conditions not tested through computer simulations, and final improved design recommendations for computation of side and base resistances for rock sockets in Texas rock formations was developed. In additions, a static rock penetrometer was developed to identify the top of a founding rock stratum while drilling with slurry.;Based on the literature reviews, field testing, and analysis, relationships between unconfined compressive strength of rock and unit side resistance and unit base resistance have been developed and related to the Texas cone penetrations. TxDOT design charts for drilled shafts socketed in rock have been updated.