The Cadillac of the drilling world going straight to the bottom of San Francisco Bay

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 preparing to blast its sturdy footings. Demolishing the reinforced concrete piers is the final step in the removal of the nearly 3km long span. In order to accomplish this complex task in an environmentally friendly way has seen a Ranger DX800 drill rig from Sandvik Construction impress with its customer focused and highly productive attributes.

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The San Francisco-Oakland Bay Bridge has already been replaced by an adjacent $6.4 billion structure that makes claim to the title of world's widest bridge. While the new bridge is impressive, so is the demolition job being undertaken by South Florida contractor Contract Drilling & Blasting LLC. The company's challenging task is effectively to make a pier disappear, cleanly, beneath the bay bottom, without disturbing the avian and marine life.

Explosive task

The drilled pier is approximately 25m wide by 40m long and stretches downward nearly100m from its cap, with the last 60m's 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 metre thick reinforced concrete walls. Holes would need to be drilled into each of the 1m interior walls as well as in 1.3m thick exterior walls. The holes were drilled in two depths — 20m and 28m — in a pattern designed to neatly capture the exploded and inward-collapsing material at the bottom of the pier's footprint. When ready for demolition, more than 558 individual electronic detonations will be separately initiated on the multiple decks, with an expected total time of 4.6 seconds.

Contract Drilling & Blasting LLC was tasked with drilling the 159 holes required in Pier E3, which was chosen to be the demonstration pier for explosives demolition. Cartridge charges are to be placed in the holes at several levels and the pier imploded without negative impacts to marine life or the environment. Environmental concerns are magnified because this is California's first major blasting demolition project in water. This means that the residue and slurry created by concrete dust cannot be allowed to degrade water quality.

In order to deal with this potential problem a system of containers were located around the drill, with all drilling residue and cuttings being collected and placed there for hauling to shore. Any aggregates were separated for reuse. During drilling it was essential that no leaks or blown hoses occur as this could lead to contamination of the water. This meant that Contract Drilling & Blasting had a big job on its hands.

Specialist expertise

The job however was approached with confidence as Contract Drilling & Blasting LLC has done similar work before, becoming renowned for its expertise in such work. 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. In fact blasting specialist for the company, Ken Tully, has recently successfully demolished bridge piers in British Columbia, Canada, which were diligently monitored for any negative environmental impact.

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, Danny 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. 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.

In order to accomplish the demolition a 15,000 kg. drill rig 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 thinness of the walls. Drilling a hole approximately 60mm in diameter for 90m's 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.

Focused drilling solution

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, the Sandvik Drilling and Stationary Crushing and Screening equipment dealer for Nevada and California, promptly supplied the machine for rental when Contract Drilling & Blasting needed it. ACS President, Mike Murphy, states: "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 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 a metre thick. 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 metre 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, who adds: "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."

Enhanced operator care

Deskins says he couldn't imagine having tackled the task with any other drill. He calls the Ranger DX800 an operator-friendly machine, stating: "The Cadillac of the drilling world. 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. 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. Electronically and hydraulically it is a great machine. Additionally, 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 has taken into consideration the comfort of the operator, which makes the job a lot easier for me."

Sandvik Construction Area Sales Manager Avery Martin says such compliments from operators are not rare. "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. 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." And as Deskins puts it: "Anything that is easier to run for the operator will increase your productivity."

The right team for the job

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. Contract Drilling & Blasting will be setting up the blast in 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. Delicate tasks like this one are doable because drilling specialists and Sandvik continue to refine the processes and equipment to do the job.