Deep Foundation Challenges at the New Benicia-Martinez Bridge

The marine piers of the new Benicia-Martinez Bridge are supported on 8 or 9 Cast-in-Drilled-Hole (CIDH) concrete piles with 2.5 m diameter permanent steel casings and 2.2 m diameter rock sockets to a depth of approximately 75 m. A Menck MHU-500 hammer was used to drive the casings up to 15 m into bedrock. The noise generated in the surrounding water unexpectedly killed fish. To resolve the environmental problem an affordable bubble curtain system was developed to reduce the sound wave energy by as much as 90 percent. Although pile driving monitoring did not detect any overstressing at refusal, some of the steel casings were found to be damaged. The damaged portions of the casings were removed and rock socket lengths were revised accordingly. Major caving occurred at Pier 8 during drilling of the rock sockets. Consolidation grouting was applied in an attempt to improve rock stability and to dimmish caving potential. However, subsequent continuous coring around the caved shaft could not confirm the effectiveness of grouting. The rotator drilling method was selected to construct the rock sockets. A pile load test (Osterberg Method) was performed to confirm the geotechnical pile capacities of the rotator-drilled shafts.