The San Francisco-Oakland Bay Bridge has been replaced by an adjacent $6.4 billion structure that claims the title of world’s widest bridge.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.
A Sandvik Ranger DX800 drill rig was selected for the challenging job. When in place, drilling took place 10 hours a day, five days a week. What made the drilling especially tricky, aside from environmental considerations, was the relatively thinness of the walls. Drilling a hole 2.75 inches in diameter for up to 86 feet with little to no deviation is not a simple task.
“The operator is given great visibility of the hole they’re drilling. Rod-changing is done with the left hand, and joy-stick drilling and boom control with the right. All pressure gauges are in the operator’s line of sight as they look at a hole,” says Sandvik Construction Area Sales Manager Avery Martin. “All in all, the cabin is designed so an operator can focus 100% on drilling. From a hydraulic point of view, one feature that makes the job easier for the operator is the Rock Pilot+ control system. It measures the hardness of the material and adjusts accordingly in order to get a straight hole.”
Three 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 to 3 feet. Another was its ability to revolve its superstructure up to 180 degrees and drill multiple holes from the same location. Those features minimize set-up time and, consequently, increase drilling time.
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, combined with Tully’s selected drill string and operator, the Ranger DX800 proved productive despite the irregular material and untrue structuring.
Eighty years after piers were constructed in San Francisco Bay to hold up the eastern span of the San Francisco-Oakland Bay Bridge, demolishing the reinforced concrete piers is the final step in the removal of the nearly 2-mile-long span
The contractor is tasked with drilling 159 holes in Pier E3, chosen to be the demonstration pier for explosives demolition. Cartridge charges will be placed in the holes at several levels and the pier imploded without negative impacts to marine life or environment. Environmental concerns are magnified because this is California’s first major blasting demolition in water. This means that the dust and slurry created by concrete dust emanating from the demolition cannot be allowed to degrade water quality.
In order to deal with this potential problem, a system of garbage cans were put 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 that no leaks or blown hoses occur as this could lead to contamination of the water.
Expertise proved vital as the structure’s vertical rebar and cross-ties tested both machine and operator, but were drilled through successfully. Other surmounted challenges included jagged surfaces on the tops of walls and soft spots in the concrete, both of which can send a drill bit skittering one way or the other.
The drilled pier is 80 feet wide by 130 feet long and stretches downward 289 feet from its cap, with the last 180 feet being 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 feet and 86 feet — in a pattern designed to neatly capture the exploded and inward-collapsing material at the bottom of the pier’s footprint. More than 558 individual electronic detonations will be separately initiated on the multiple decks, with an expected total time of 4.6 seconds.
The estimated time needed to actually destroy the pier after it has been drilled and laced with electronically sequenced explosives is less than six seconds. The blast was slated for November 2015. The month was selected because demolition during the period poses the least risk to San Francisco Bay’s fish and wildlife populations, including porpoises, sea lions and seals.
Sandvik is a high-tech and global engineering group offering advanced products and services that enhance customer productivity, profitability and safety. The group specializes in tools for the mining and construction industries, among other things. In 2014 the Group had about 47,000 employees and representation in approximately 130 countries. To learn more, go to www.sandvik.com.