PROJECT OVERVIEW
Phoenix Project #2015
This project called for underpinning of an existing brick and mortar foundation that was part of a Historic Carriage House located at the Mary Baker Eddy House just outside of Boston, MA.
Phoenix was contacted by Consigli to develop a proposal to underpin the sensitive existing foundation. With safety being paramount, Phoenix worked with GZA GeoEnvironmental, Inc. to develop an alternate underpinning design concept to be used in lieu of traditional underpinning pits. This innovative foundation support system would transfer the load of the existing foundation into a micropile-supported grade beam system. In addition to providing safe support of the existing building and foundation to facilitate nearby new construction, it was also imperative that our final design considered the historic preservation of the building.
Once the foundation support system was approved, Phoenix first installed the drilled micropiles. They consisted of permanent flush-joint steel casing advanced to the top of bedrock, followed by an uncased rock socket. After GZA had installed numerous settlement monitoring points on the building, Phoenix was able to utilize a down-the-hole hammer system to install the micropiles into bedrock, resulting in significant cost and schedule savings to the project without risking damage to the existing building. The building was monitored in real time as piles were installed and no vibration thresholds were ever exceeded.
After pile installations were completed, Phoenix selectively cored holes through the building’s foundation, which were later reinforced to incorporate into the grade beams. Thereafter, soft excavation techniques were used to remove soil and parts of the foundation system to a prescribed subgrade elevation. After the excavation was completed, the concrete subcontractor formed, tied, and poured the new grade beam system over the drilled micropiles.
The forms were stripped after the new concrete had reached design strength, and the site was backfilled. The building was then restored to its original finish by others, leaving no visual markings of Phoenix’s foundation support system.
