The Last Blast

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Construction of the Albert Sherman Center moved into a new phase this September, with workers beginning to build up after months of digging down.

Friday, Aug. 27, marked the final blast at the building site, capping a three-month program to break up some 20,000 cubic feet of rock that needed to be removed. The following week, as excavation of the blasted rock continued on the lower portion of the site, the first load of structural concrete was poured to begin forming the retaining walls and foundation of the upper portion of the nine-story building.

“The last blast and first concrete pour are two significant milestones in this project,” said John Baker, associate vice chancellor for Facilities Management at the Medical School, who is overseeing the project. “The campus community was very patient and understanding during the blasting, and we came through it all with very minimal impact. The blasting team did a great job.”

For the next several weeks, excavation of blasted rock will continue and the bottom of the site will be inspected and prepared for foundation construction. While blasting is an engineered process designed to be as precise as possible, the variability of rock means some adjustments are usually needed to smooth out the base of a site after blasting.

“After an area is blasted and excavated, we go down to inspect,” said Matthew Grzywacz, field engineer for McPhail Associates, the geotechnical engineering firm that monitors the blasting, excavation and site conditions during construction. “The rock at the bottom needs to be at the right elevation, relatively flat and suitable for the footings that will hold up the building.”

Once the area is inspected, a large jack hammer attached to the end of a backhoe is used to chip the rock to the desired profile. Sometimes drilling rigs are used to drill multiple holes in the remnant rock to weaken it so the jack hammer can remove it— a process the workers call “Swiss-cheesing the rock.”

Once the excavated area meets McPhail’s criteria, installation of the footings and structural elements that will hold up the building can begin. In some areas, that means 50-foot-long steel shafts called rock anchors are drilled into the bedrock to anchor concrete footings for the building. In other areas, large concrete retaining walls, reinforced with steel bars, are poured to form part of the foundation of the building.

Meanwhile, outside of the green-fenced construction perimeter, work will continue for several weeks on the installation of utility lines and infrastructure needed to service the new building. “We are very pleased with the progress being made on the project,” Baker said.

Structural steel will begin to rise from the foundation in late fall. The building is scheduled to open in 2012 and will house several research centers including the Advanced Therapeutics Cluster (ATC), where teams will work to develop innovative therapies for a range of human diseases.