Berth Deepening by Rock Blasting at the Howland Hook Marine Terminal, Staten Island, NY

Instrumentation of a marine terminal during close-in underwater blasting included in-rock and wharf-mounted geophones and water pressure sensors adjacent to piles. Limits placed on vibrations and pile cap shear strains were 25 in/s (635 mm/s) and 467 µ-strains (safety factor of 4). Pile cap and wharf deck strains were calculated from time-correlated displacement measurements during 42 blasts up to 9 ft (2.7 m) from the wharf. The highest ground velocity and acceleration adjacent to piles were 46 in/s (1,068 mm/s) and 95 g’s while the highest pile cap strain was 435 µ-strains. Peak frequencies averaged 200 Hz (0.005 s period). Peak concrete deck bending and tensile strains were 15.5 and 9.7 µ-strains, respectively. The wharf sustained no damage at these strains. Structure response spectra were computed for the largest expected earthquake and compared with a typical blast demonstrating that structure displacements and strains at the wharf natural period are lower for blasting.