Equipment Tag Team
Equipment Tag TeamConcrete pumps and belt conveyor take turns to raise challenging construction project
out of a 70-foot (21.34m) deep hole
STURTEVANT, WI (May 26, 2009) – Confronted with numerous job site obstacles, including no way to drive construction equipment into a 70-foot (21.34m) deep hole, contractors turned to the technological features of Putzmeister concrete pumps and unique characteristics of Telebelt® telescopic belt conveyors to place concrete and stone when building an underground parking structure.
The seven-level parking garage, constructed underneath the rising 14-story Yawkey Center for Cancer Care, is part of the new $250 million Dana-Farber patient care and clinical research facility being developed in Boston’s Longwood Medical Area.
The project broke ground in June 2007 under the direction of general contractor Walsh Brothers, Inc., of Boston, Massachusetts. Multiple concrete pumps and a belt conveyor went to great depths to place concrete and stone when raising the project out of its 70-foot (21.34m) deep and 180-foot (54.86m) by 200-foot (60.96m) wide hole.
J. Derenzo Company (Derenzo) of Brockton, Massachusetts, one of the East Coast’s most experienced site development specialists, performed the excavation and earth support. To place stone and pump a controlled low strength concrete called flowable fill into difficult-to-reach areas, the contractor relied upon the L. Guerini Group (Guerini) of Boston, Massachusetts, for its expertise as well as diverse product line of concrete line pumps, boom pumps and belt conveyors. The various equipment models, selected for their specific reach, setup and boom configuration capabilities, would take turns tackling different placing challenges during the excavation stage.
First On Site
The first concrete pump on site was a VS 2070 truck-mounted Thom-Katt® line pump. It pumped 300 cubic yards (229m³) of flowable fill during construction of an underground tunnel that would connect campus buildings. Strategically setup under a temporary bridge, the pump was relied upon for its 750-psi (52 bar) maximum pressure and up to 70 cubic yards an hour (54m³/hr) output to push the mix through delivery line exceeding 150 feet (45.72m).
Accessing Tough-to-Reach Spots
Months later, a truck-mounted 20Z-Meter concrete boom pump arrived on site to access a difficult-to-reach slab. The unit deployed its compact outriggers, only 11 feet two inches (3.40m) in the front and eight feet six inches (2.59m) in the rear, and set up on a specially constructed concrete platform that serves as a mechanical room’s roof. The 20Z then employed the flexibility of its unique four-section Z-Fold boom to reach down and extend through a narrow opening underneath the same platform the machine was set up on. By further maneuvering its versatile 63-foot ten-inch (19.46m) long boom, it provided the ideal boom configuration and precise reach needed to pump 40 cubic yards (31m³) of flowable fill as a base for the mechanical room’s slab.
“Without the boom pump, there was no other way to access this area,” says John Bowen, Derenzo’s project superintendent. “It was an unusual site to see the boom literally extended underneath itself to pump the 200-foot (60.96m) wide slab.”
Working on the Edge
The main feat of the excavation work was the removal of 120,000 cubic yards (91,747m³) of dirt to build a slurry wall foundation, which encased all sides of the structure and consumed 12,000 tons of concrete, 700 tons of reinforcing steel and 286 tie-backs. Upon completion of the slurry walls, the excavation crew was faced with a large hole that required flowable fill around caissons, piers and a storm water ejector pit as well as stone backfill for the entire base.
The task had to be accomplished without a driveway or path to the bottom of the hole for construction vehicle access. Further compounding the situation was a congested job site, tightly sandwiched between buildings on three sides and a busy street on the fourth, of which only two sides could be used to set up equipment.
To overcome these job site conditions, boom pumps and a belt conveyor teamed up to place concrete and materials from the edge of the deep cavity. Initially, a Putzmeister 43-meter boom pump, with its 99-foot one-inch (30.20m) reach depth, was called upon to extend its boom down into the hole’s base to place flowable fill around circular caissons. Set up within a confined area, the unit deployed its front and rear outriggers at a 28-foot (8.53m) spread, extended its long boom over the edge of the void and utilized its free flow hydraulics to efficiently place the lean mix with smoothness and precision.
Placing Stone with Safety and Speed
Next, stone needed placement at a one-foot (.30m) depth over the entire base. To accomplish this task with the greatest efficiency, Derenzo turned to the long-reach and high-volume capabilities of Guerini’s TB 110 telescopic belt conveyor. The belt conveyor extended its boom 106-feet one-inch (32.34m) horizontally to the middle of the hole. The unit quickly conveyed ¾-inch (19mm) stone, which was discharged into the conveyor’s low profile hopper.
“With the high outputs of the belt conveyor, we emptied a 22-ton truckload of stone in less than ten minutes, which kept the project moving at a fast pace,” says Bob Magliozzi, one of four family owners at Guerini, a highly experienced third-generation construction business established in 1917.
Other alternatives for placing stone on site were not feasible, as Magliozzi notes, “Backing up trucks to dump stone over the edge would have been dangerous, a scoop and cast method would have splattered a lot of stone, and there were job site restrictions as well as little room to stockpile stone at street level.”
“The owner was especially concerned about job site safety as well as controlling construction dust to keep it from bothering respiratory patients entering the medical center,” says Bowen. “Therefore, the Telebelt was the logical choice to safely place 2,000 tons of stone. To prevent dust, we sprayed water on the stone as it went into the hopper.”
“With the conveyor, we could place it directly from the truck to the bottom of the hole so we didn’t need to stockpile stone on the job site,” adds Bowen. “Plus, the machine’s long reach meant we could place it in the middle of the 200-foot (60.96m) hole instead of just at the edge. This helped cut our re-handling costs in half.”
Pumping Flowable Fill with Precision
The equipment tag team approach continued, as Guerini’s 36-meter boom pump was dispatched to place 200 cubic yards (153m³) of flowable fill around various piers before the conveyor returned to backfill more stone. The 36-Meter boom pump revisited the job site, using its compact outrigger spread to setup in a tight area and 79-foot eight inch (24.28m) reach depth to access a storm water ejector pit that required 80 cubic yards (61m³) of the lean mix.
Commenting on the capabilities of the different placing equipment and its various operators, Bowen says, “Guerini operators certainly know how to run their equipment. They quickly set up their machines and maneuver the booms exactly where needed. We’ve used their equipment in the past, and have never experienced a single breakdown.”
Adding to the excavation job’s on-time completion was the detailed coordination in scheduling dump trucks and ready mix trucks, which could not be staged near the busy job site for fear of clogging ambulance routes. Derenzo’s trucks hauled stone supplied from West Roxbury Crushed Stone Company of West Roxbury, Massachusetts; and Aggregate Industries, Inc. dispatched concrete from various Massachusetts-based plants within its Northeast Region Ready Mix Division.
Building a Solid Foundation
Once the excavation work was well underway, foundation work started under the direction of sub-contractor G&C Concrete Construction, Inc. (G&C) of Haverhill, Massachusetts. G&C employed the concrete pumping services of D&M Concrete Equipment, Inc. (D&M) of Fall River, Massachusetts, an authorized Putzmeister distributor. Established in 1974, D&M provided vast experience and the equipment needed for placing approximately 2,600 cubic yards (1,988m³) of concrete for walls, columns and various flatwork.
Numerous concrete pump models were utilized from the company’s fleet. This included a VS 1408 truck-mounted City Pump for pumping concrete through long delivery line that was routed inside an existing building during an overnight pour, a 47Z-meter utilized for its long 151 foot three inch (46.10m) vertical reach and a 36Z-meter boom pump, which handled the lion’s share of the pumping for the 36,000-square foot (3,345m²) foundation.
Excavation and foundation work finished in October 2008, and the building continues its construction upwards. When completed in 2011, the new center will bring Dana Farber's total space to approximately 1.85 million square feet (171,870m²).