New power service through an occupied building

The job

An existing downtown building needed a new electrical service. A new cast-in-place transformer vault had to go in an interior courtyard, and the conduits had to get there from the alley: about eight feet deep along the building, then through the basement, climbing fast enough to stay clear of the column footings.

What made it hard

The courtyard is enclosed on every side by the building. There is no gate, no driveway and no opening a machine can pass through. We closed a downtown avenue, set up a crane in the street, and lifted the excavator over the four-story building and down into the courtyard.

Close to 700 yards of courtyard spoils left the site on conveyor belts through a ground-floor unit to a dump truck waiting in the alley. Inside the building we saw-cut the slab and hand dug a trench up to eleven feet deep, passing the dirt out through a window opening.

Rock went in the way the dirt came out. Our CAD Truck set up in the alley and placed the rock through the building and into the courtyard excavation.

The courtyard also held two large buried heating oil tanks. We decommissioned both, and exported roughly four dump truck loads of native soil that had been contaminated with heating oil.

The alley is paved in historic brick. We lifted the bricks, cleaned and palletized them, and delivered them back to the city before opening the trench.

What we brought to it

The general contractor came to us because nobody on the team could see how to build it. More than one person considered the work infeasible. They brought us a series of compounding problems and asked whether it could be done at all. We worked through several unconventional approaches and came back with the plan that let the project move forward.

• We reviewed the duct bank layout before the work started and told the team where the bends would not fit as drawn, with a proposed route that would.
• We recommended leaving an old side sewer in place rather than digging it out next to the foundation, and explained the risk to the building.
• The alley trench was shored, and covered with steel plates at the end of every day.
• The duct bank was encased and the trenches were backfilled with CDF.