WorldWide Drilling Resource

Blasting a Bridge to the Bottom of a Bay Takes Skill Adapted from a Case Study by Sandvik Construction Eighty years after piers were constructed in San Francisco Bay to hold up the eastern span of the San Francisco-Oakland Bay Bridge, a specialized contractor is blasting its sturdy footings. Demolishing the reinforced concrete piers is the final step in the removal of the nearly two-mile long span. To accomplish this complex task in an environmen- tally friendly way, a Ranger DX800 drill rig from Sandvik Construction has been working on-site. The San Francisco-Oakland Bay Bridge has already been replaced by an adjacent $6.4 billion structure which claims the title of world’s widest bridge. While the new bridge is impressive, so is the demolition job being undertaken by Florida contractor Contract Drilling & Blasting LLC. The company’s challenging task is to make a pier disappear cleanly beneath the bay bottom without disturbing the bay’s avian and marine life. The contractor is tasked with drilling 159 holes in Pier E3, chosen to be the demonstration pier for explosives demolition. Cartridge charges were placed in holes at several levels and the pier imploded without negative impacts to marine life or environment. Environmental concerns were magnified because this was California’s first major blasting demolition in water. This means the dust and slurry created by concrete dust from the demolition could not be allowed to degrade water quality. To deal with this potential issue, a system of garbage cans were placed around the drill, and all drilling residue and cuttings were collected and placed in a covered container exclusive for aggregates for hauling to shore. It was essential no leaks or blown hoses occur as this could lead to contamination of the water. The drilled pier is 80 feet wide by 130 feet long and stretches downward 289 feet from its cap, with the last 180 feet drilled into the muddy bottom of the bay. Beneath the pier’s cap is a supporting grid honeycombed with voids. Horizontal cross-sections periodically intersect with three-foot-thick reinforced concrete walls. Holes were drilled into each of the three-foot interior walls as well as in four-foot- thick exterior walls. The holes were drilled in two depths - 64 and 86 feet - in a pattern designed to capture the exploded and inward- collapsing material at the bottom of the pier’s footprint. More than 558 individual electronic detonations were initiated on the multiple decks. Blasting specialist for Contract Drilling & Blasting Ken Tully, was responsible for designing the blast, overseeing the drill operations, and conducting the blasting operations. He specifically chose a Sandvik Ranger DX800 drill rig for the challenging job. “I wanted this machine. I have used similar Sandvik equipment on other projects and was very satisfied. The accuracy and trueness of the holes was fantastic.” Tully has worked around Sandvik drilling rigs for 20 years and said he has al- ways been impressed with their productivity. He believes several features on the Ranger DX800 were critical on drilling Pier E3. One was the rig’s reach, which in the limited pier area can be very difficult and sometimes up to 2-3 feet. Another was its ability to revolve its superstructure up to 180 degrees and drill multiple holes from the same location. The other critical feature was Sandvik’s TIM5300 system, which measures depth and inclination to a high degree of accuracy. The enhanced drilling accuracy of the TIM5300 was needed because the pier’s three-foot-thick walls were poured in place, sometimes in multiple pours, and were not expected to always run true. Guided by the system, the Ranger DX800 proved produc- tive despite the irregular material and untrue structuring. “There were lots of surprises and adjustments to make, but we made them successfully,” said Tully. 44 JANUARY 2016 WorldWide Drilling Resource ®