November 26, 2007
Yawkey Center Construction Update
Workers install tiebacks in the construction area
There has been "tons" of progress in construction of the underground parking garage for the Yawkey Center for Cancer Care since the project began a year ago.
Nearly 12,000 tons of concrete and 700 tons of reinforcing steel were used in building the garage's "slurry walls," which extend up to 106 feet into the ground and form the sides of the structure. Since the completion of the slurry walls in mid-July, crews have dug and carted away more than 20,000 tons of dirt from the site, the first of 140,000 tons that must be removed in all, says Senior Project Manager Joe Bassi. By the time excavation is completed, some 4,100 truckloads of material will have been taken away.
As the digging continues, crews are installing the first of 286 tiebacks that will anchor the slurry walls and prevent them from bulging or giving way once all the dirt inside is removed. Tiebacks are 120- to 140-foot bundles of reinforced steel rods that anchor the slurry walls to bedrock through holes drilled at a 45-degree downward angle. Ten tiebacks have been installed so far, running under Jimmy Fund Way and the Mayer and Dana buildings, Bassi says.
When all the tiebacks are in place, their shafts would extend 5.5 miles if placed end to end, Bassi continues, and the 75 miles of steel cable within them will weigh 148 tons. Approximately 950 tons of grout will be poured into the shafts around the cables.
Meanwhile, along Brookline Avenue, workers have constructed a concrete platform for a plaza and outdoor seating area in front of the Yawkey building. The platform also serves as the roof of the building's mechanical room, where heating, cooling, and air-handling equipment will be housed.
Along Jimmy Fund Way, crews are building what will become a new patient drop-off area. And under Jimmy Fund Way, they have completed a tunnel from the Yawkey building to the L2 level of the Dana building. Though the tunnel is now in place, workers won't "punch through" to Dana for a couple of years, Bassi comments.
The project is right on schedule, reports Project Executive Thomas Herring, and has resulted in only three minor injuries to workers. The major wrinkle in the excavation work was the discovery in March of three underground gasoline tanks that had ruptured and spilled gas into the surrounding soil. Trucks carried the affected soil to a processing plant in New Hampshire for decontamination. In late September, crews unearthed an old heating oil tank that had also leaked, though not as badly as the gas tanks, Herring notes. The contaminated soil was trucked to a Massachusetts plant for processing. Clean soil from the site has been carried to construction sites for new subdivisions in Massachusetts and Rhode Island.
Construction has continued for more than 450 days without an accident requiring a worker to miss time on the job, Bassi notes. Since November of last year, more than 70,000 labor hours have gone into the project, the equivalent of one person working eight hours a day for 35 years.
One of the biggest challenges of the project has been the need to minimize settling of the ground under of the Medical Area Total Energy Plant (MATEP) next door as workers bore tieback shafts in that area, Herring remarks. Project engineers have worked closely with engineers at MATEP to mitigate such settling.
The onset of cold weather and possibly snow shouldn't slow down activity, Bassi says. Snow is simply plowed to an unused section of the site, and if cold weather causes water lines to freeze, crews arrive early to warm them up.
"We've got a great team, and we're progressing at a good pace," Herring says. "Everything is on or ahead of schedule."
