Case history evaluation of the behavior of drilled shafts under axial and lateral loading. Final report

Drilled shafts are used frequently as the foundations for electrical transmission line structures. These structures are subjected to gravity dead loads, vertical live loads such as ice, and lateral wind loads. With these loads, foundation design is dominated by axial and lateral loading. This study is a critical evaluation of drilled shaft behavior under axial and lateral loading for undrained and drained conditions. A wide variety of field and laboratory load test data were used for this evaluation. The geotechnical and load test parameters were evaluated using updated methods that consider all appropriate corrections to standardize the data base to a consistent reference plane. In axial loading, both side and tip resistances were analyzed. The side resistance was evaluated using both the alpha and beta methods, and the tip resistance in compression was evaluated using bearing capacity theory. In lateral loading, different available analytical models for lateral capacity were compared with two interpreted capacities, the hyperbolic capacity and the lateral or moment limit, from the load test results. The relationships between the theoretical models and interpreted capacities were presented, including the lower and upper bound lateral capacity values. The effect of shaft rigidity on the lateral capacity also was evaluated,more » and the differences for rigid, intermediate, and flexible shafts were demonstrated. Specific design recommendations for drilled shafts were developed and are given with the appropriate statistics to describe the quality of the recommendations.« less