Placing Booms Tag Team Deep Shaft
It’s a sign of the times, as American cities look hard at infrastructure that is taxed beyond its design capacity. That is the case in Washington D.C. where heavy rains can overwhelm the sewer system causing flooding and overflow into neighboring rivers. Traylor Brothers, Evansville, IN, known for taking on challenging heavy civil projects, has embarked on a two-year contract in a joint-venture Traylor/Skanska/Jay Dee, to alleviate combined sewer overflows that pollute the nearby rivers. A 24,000-foot tunnel, with minimum diameter of 27-feet, is being bored under and adjacent to the Potomac and Anacostia rivers through soft ground utilizing a tunnel-boring machine. Brundage-Bone & Blanchet, LLC (BB&B), Laurel, MD is utilizing pumping and placing equipment to finish a massive vertical shaft that will consolidate dewatering equipment for the project. The 185-foot deep drop shaft is 139-feet in diameter requiring an innovative method of concrete placement that utilizes two separate placing booms with two different mounting methods.
“Because of the size of the shaft most people take a step back when they view it from the observation deck over the hole,” according to BB&B’s President Matt McDonald, “The job required pumping a mat or “plug” in the bottom and perimeter walls for this giant cylinder. Execution required volume and speed.” Brundage-Bone Blanchet in concert with Traylor Bros.’ personnel, designed a system of concrete placement that has two different boom mounting methods for the 13,000 cubic yard plug and 13,000 cubic yard walls. The gravity fed drop shaft will dewater and store overflow. It will feed a tunnel directly underneath it from two outlets. “Because the base would be poured in five-foot lifts, we needed a mounting system that would provide maximum coverage from two separate placing booms,” explains McDonald, “We decided on a wall mount system that was designed from our input and engineered and built by Traylor with help from Schwing.” The first mounting method had the two booms placed 180-degrees apart in the shaft. Separate pipelines feed each boom with pumps on street level.
The 4-section Roll and Fold booms with 113-feet of horizontal reach are detachable Schwing 39-meter units from BB&B’s extensive pumping fleet dispatched from yards in Maryland, Virginia and Pennsylvania. “These booms proved to be invaluable maneuvering around and under the platforms,” McDonald explains, “Other booms just don’t have the ability to work close to the turrets.” The booms detach from truck-mounted pump units and are flown to their perches by cranes on the surface. “Moving the booms off the trucks was made simple by the Schwing units’ quick detach system,” explains McDonald. “The booms can be removed and quickly pinned in place on the platforms. This is important as crane time is at a premium on a project like this.” Pipelines were run straight down the shaft to the base of the placing booms and turned 90-degrees twice to connect to the booms. This was done to slow down the velocity of the falling concrete before going into the tighter elbows on the boom. Additionally, spade valves were installed at each boom to prevent concrete from draining through the pipeline when pumping was halted. “Because the concrete was similar to a self-consolidating mix design, with a very high slump and very little water, we didn’t want to have issues with segregation from free-fall,” according to McDonald. Each lift consumed approximately 2,600 yards with pumping volume averaging 120-150 yards per hour limited only by ready-mix deliveries. The truck pumps on the surface were capable of up to 208 cubic yards per hour utilizing 2023-5 pump kits and the time proven Rock Valves.
Phase 2 of the concrete pumping involved wall pours to complete the shaft. Mounting the same booms to the top level of the massive base allowed the wall forms to be unhindered by the previous boom mounting brackets. Schwing octagonal masts were used for ease of set-up with only two embedded bolts anchoring each leg of the cross frame base and no counterweights on the booms. One six-meter mast section was used for each placing boom. A universal head section mounts to the mast and accepts all sizes of Schwing separate placing booms. A four-pin quick-connect system attaches the boom to the head section. Pipelines were routed through an adjacent drop shaft to a horizontal tunnel below the pour area and turned 90-degrees to connect to the booms. BB&B and Traylor crews were able to erect the two masts in the center of the shaft and quickly reroute and mount the pipelines, operator platforms and ladders to brackets welded to each mast section. If higher elevation is needed, mast sections can be combined by simply bolting them together.
With this method, the two booms continued wall pours simultaneously averaging approximately 60 yards per hour each to raise the four-foot thick walls 75-feet. “With 78-feet of vertical height left, we switched to boom pumps on the surface to fill the wall forms,” McDonald explains, “Our Schwing 52 and 55-meter pumps easily reached down to complete the job.” The entire pumping portion of the drop shaft project was completed over an eight-month period. Traylor Bros. expects to be completed with the tunneling by the end of the year.
Owner: District of Columbia Water and Sewer Authority, Washington D.C.
Tunnel Contractor: Traylor/Skanska/Jay Dee Joint Venture. Washington D.C.
Pumping Contractor: Brundage-Bone Blanchet LLC, Laurel, MD
Pumping Equipment: 2 Schwing KVM 39 X 2023-5 truck-mounted concrete pumps with detachable placing booms with octagonal mast system, 1 Schwing KVM 52 2525-6 and 1 KVM 55 2525-6 truck-mounted concrete pump with placing booms.