July 11, 2008
Slurry wall construction: Building a foundation for the future

Now that the demolition of the Clinics, Tilton and Vincent Burnham Kennedy buildings has been completed and the site cleared, construction of the new clinical facility, the Building for the Third Century (B3C), begins a new phase. Onlookers can expect to observe the first step of the creation of the building's foundation — the construction of the slurry wall.

The slurry wall process results in the construction of a concrete wall perimeter that sets the stage for the excavation of the underground floors and essentially creates the basement walls of the new building. Already, construction crews have prepared the site for the slurry wall phase that begins this month and ends in December.

The first step includes the digging of 41 trenches each approximately 20-feet-wide, two-and-a-half-feet-thick and 100-feet-deep around the perimeter of the site. Approximately two to four digging operations will occur each day along the perimeter throughout the next months. In the center of the site, construction workers will be building steel cages to fit inside each trench.

Clamshell digger cranes will create the trenches, excavating the soil, which will be loaded onto trucks and taken away via Charles Road. Approximately 11,000 cubic yards of earth will be removed during the six months of slurry wall construction.

slurry wall construction

A finely tuned operation: The slurry wall process continues around the site perimeter in alternating sections until all wall sections are installed and a continuous concrete foundation wall is in place.

As each trench is dug, it is filled with slurry, a heavy liquid consisting of bentonite and resembling a thick brown milkshake. Filling the trench with slurry prevents the hole from collapsing during excavation. As the clamshell excavators pull out soil through the slurry, the soil becomes loose as it is loaded into trucks at the surface.

After the trenches are dug, large reinforced steel structures resembling cages will be hoisted by crane and vertically inserted into each slurry-filled trench. It is important to note that during this step traffic temporarily may be rerouted for a short time along the White Ramp and Fruit Street for safety purposes, and pedestrians may be redirected to alternate paths by MGH Police and Security. Once the cage is in place, concrete is placed into the trench, displacing the slurry. At the same time, the slurry is pumped out and reused for another panel. This process continues along the perimeter in alternating sections until all wall sections are installed. The concrete inside each trench "cures" or hardens over a period of several days.

Following the slurry wall construction phase, up-down construction will begin during the winter months. This involves the simultaneous digging of the four underground levels and the building of the structural steel frame for the 10 aboveground floors.

Vibrations and noise from ongoing construction may be noticeable throughout construction of the B3C, which is scheduled to be completed in in 2011. With the Thrive B3C Operations Committee and its Noise, Vibration and Particulate Subcommittee and contractors working together, individuals can be assured that all precautions are being taken and safety is paramount. MGH staff and employees are encouraged to report any construction-related concerns at any time to their supervisors or to the MGH Buildings and Grounds Call Center at (617) 726-2422. For more information about the B3C, visit www.massgeneral.org/building3c.

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