Phoenix Project #1916
Carved into the side of a hill more than 60 feet tall, a new academic building was envisioned at Worcester Polytechnical Institute (WPI)’s main campus. Phoenix was selected to design and install nearly 9,000 square feet of temporary support of excavation (“SOE”) to facilitate this new construction. While the bid documents called for the use of traditional pre-drilled soldier piles and timber lagging, concerns of subsurface obstructions as well as challenging site access made this method impractical. Instead, Phoenix developed an alternate design approach that helped mitigate the Owner’s obstruction risk and also maintain the project schedule, without compromising safety or quality.
Working in tandem with our client (Northeast Contractors, Inc. of Ludlow, MA), Phoenix first installed more than 70 drilled micropiles (DMPs) along the perimeter of two distinct SOE systems. As soon as the piles were installed, Northeast progressed the site excavation and Phoenix performed “contact lagging” between the piles to retain the soils. For this method, threaded bolts were welded to the face of each pile and steel plates were fastened to each bolt in order to secure the timber lagging boards in place. Due to the high grade of steel piles used (in excess of 100 ksi), extreme care and proper welding techniques were critical to ensure quality welds, especially in the cold winter temperatures.
With excavations ranging from less than 10 feet to nearly 30 feet in depth, Phoenix used several different design and construction methods (cantilevered, internally-braced, and externally-braced) to maximize the efficiency of the SOE in each case. The internal bracing system consisted of over 250 linear feet of continuous beam walers supported by pipe and beam struts, and external support was provided in two isolated areas utilizing temporary tiebacks.
Ultimately, Phoenix and its client were able to execute this challenging project – safely and on time. And in so doing, we were able to help the Project recover some unforeseen schedule setbacks incurred prior to the start of our work.