A plumbing contractor hand tunneled 140LF of 4’x5′ tunnel under two apartment buildings near Boston, Massachusetts. In preparation for a renovation project, a structural inspection was performed. The structural inspection revealed the slab floors which were tunneled under were not designed as structural slabs. The structural engineer directed the property owner to immediately fill the tunnels to restore structural integrity.
The tunnel abandonment work had to be completed during the winter, and while one of the two affected buildings was occupied. The non-occupied building was also in the process of asbestos abatement and a full gut renovation.
Due to the plumbing run through the tunnels, an excavatable grout was required. Also, grout had to be low exotherm in order to not affect the new PVC plumbing.
CJGeo proposed polyurethane grouting for the tunnel abandonment. Polyurethane grouting can be performed in any weather, is low exotherm, and can be placed in very thick lifts. The specific grout chosen was a low exotherm bulk void filling polyurethane.
CJGeo mobilized a polyurethane grouting truck with more than 9000 pounds of polyurethane grout, due to the unknown exact volume of the tunnels. During a 8″ snowstorm, CJGeo abandoned both tunnels in a single day. The unoccupied building was grouted via holes drilled through the floor. The tunnel below the occupied building was free sprayed from inside the tunnel. All tunnels were kept under negative pressure ventilation in order to address installation odors.
CJGeo placed 4100 pounds of polyurethane grout into the two tunnels.