Phoenix Project #2009
When a section of retaining wall along the MBTA commuter rail line supporting Route 129 was determined to be in a state of disrepair, Phoenix was contracted to install permanent soil nails and shotcrete to repair the wall.
Due to the close proximity to an active railroad corridor, all soil nail and shotcrete installations had to be performed during limited overnight shifts. In addition to the reduced work hours, every night-shift was further impacted by a single train rolling through. This required all equipment being removed from the tracks and moved out of the foul zone (the 4’ area on either side of the tracks).
While the limited and interrupted work window was a hindrance, an equally difficult challenge facing our work were the massive granite boulders that had been unknowingly placed behind the retaining during its original construction. At multiple nail locations, granite boulders had to be penetrated, with cores up to 4 feet in length retrieved while drilling.
Prior to shotcrete placement, Phoenix drilled hundreds of holes into the face of the existing retaining wall, and set hooked dowels and epoxy resin into each hole. These dowels were used to support welded wire fabric that provided the permanent reinforcement of shotcrete installation. Thereafter, a 4-inch thick layer of shotcrete was installed over the face of the existing wall.
After the shotcrete had been placed, soil nails were installed with a limited access track-mounted drill rig. In certain areas, the rig and crew had to be elevated using wooden and Styrofoam mats in order to reach the highest soil nails along the existing wall alignment. Following their installation, each soil nail was locked off against the new shotcrete facing using epoxied coated bearing plates and hex nuts.