Bottoms up

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 was preparing to blast its sturdy footings. Demolishing the reinforced concrete piers was the final step in the removal of the nearly 2-mile-long span.

The San Francisco-Oakland Bay Bridge has already has been replaced by an adjacent $6.4 billion structure that claims the title of world’s widest bridge.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. In order to accomplish this complex task in an environmentally friendly way, a Ranger DX800 drill rig from Sandvik Construction worked on-site with customer-focused and productive features.

The contractor was tasked with drilling 159 holes in Pier E3, chosen to be the demonstration pier for explosives demolition.

Cartridge charges were placed in the 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 that the dust and slurry created by concrete dust emanating from the demolition could not 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. Clearly, Contract Drilling & Blasting had a big job on its hands.

HAVING A BLAST

The job was, however, approached with confidence as the contractor has done similar work before, though perhaps not under such tight environmental restraints.

The company has developed a first-class reputation in its field and now travels the world undertaking specialized blasting and demolition projects. This includes the demolition of marine structures and bridge superstructures, as well as other underwater blasting projects.

Blasting specialist for the company, Ken Tully, has recently successfully demolished bridge piers in British Columbia that were diligently monitored for any negative environmental impact. He was the controlled blasting specialist for the E3 demolition project. Tully was responsible for designing the blast, overseeing the drill operations and conducting the blasting operations.

This emphasis on employee expertise on the project saw Danny Deskins drill the holes in the demonstration pier. Though Pier E3 was the first pier he worked on, Deskins is a 26-year veteran of precision drilling, and was able to meet the challenges head on. His expertise proved vital as the structure’s vertical rebar and cross-ties tested both machine and operator, but were drilled through successfully.

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 was a supporting grid honeycombed with voids. Horizontal cross-sections periodically intersect with 3-foot-thick reinforced concrete walls.

Holes were drilled into each of the 3-foot interior walls as well as in 4-foot-thick exterior walls. More than 558 individual electronic detonations were to be separately initiated on the multiple decks, with an expected total time of 4.6 seconds.

PRECISION DRILLING

In order to accomplish the demolition, a 37,000-pound drilling machine was crane-loaded onto a barge, floated to the pier, and offloaded atop it. When in place, Deskins drilled 10 hours a day, five days a week.

What made the drilling especially tricky, aside from environmental considerations, was the relatively thin 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 trick was getting to the bottom of the hole without going out one side of the wall,” Deskins says.

Tully 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.”

Aggregate Crusher Specialists (ACS), the Sandvik Drilling and Stationary Crushing and Screening equipment dealer for Nevada and California, supplied the machine for rental. ACS President Mike Murphy, says, “Time is of the essence in this industry; we strive to be able to supply the right equipment and the best service at the right time. Barry Wells, our drill specialist, was present on-site the first few days of the drill arriving to the pier and supplied the technical support during the project.”

Tully has worked around Sandvik drilling rigs for 20 years—including with predecessor Tamrock units—and says he always has been impressed with their productivity.

The blasting specialist believes several features on the Ranger DX800 were critical on drilling Pier E3. One was the rig’s reach, and 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.

Another critical feature was Sandvik’s TIM5300 system, which 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. “There were lots of surprises and adjustments to make, but we made them successfully,” says Tully. “This project was undertaken in a controlled drilling atmosphere rather than a production drilling atmosphere. I would rather take an hour on a single hole than quickly drill a bad one.”

Deskins calls the Ranger DX800 an operator-friendly machine. “You really need to be precise and pay attention to the hole you are drilling, but the cabin is comfortable and you don’t have to stretch a long way,” he describes. “The TIM5300 system will keep up with the penetration rate, which makes it quicker for me to go through from one hole to the next.”

He adds, “The pier environment is a small space; you can get lots of people on the pier around you but the cameras in the cabin allow me to see everything around me.”

Sandvik Construction Area Sales Manager Avery Martin elaborates. “The operator is given great visibility of the hole they’re drilling. Rod-changing is done with the left hand, and joystick drilling and boom control with the right,” he says. “All in all, the cabin is designed so an operator can focus 100 percent on drilling.”

The Rock Pilot+ control system feature of the machine measures the hardness of the material and adjusts accordingly in order to get a straight hole.

It took less than six seconds to actually destroy the pier after it was drilled and laced with electronically sequenced explosives.

Contract Drilling & Blasting set up the blast in Nov. 14, 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. Delicate tasks like this one are doable because drilling specialists and Sandvik continue to refine the machines that can do the job.

Giles Lambertson is a freelance writer who has been writing about the construction industry for nearly two decades. This article was submitted by Sweden-based Sandvik Construction, which has its United States head office in Smyrna, Georgia.