A stone wall that supports the Norfolk Southern rail line developed a cavity measuring 22 feet high and 48 feet wide. This wall needed reinforcement in order for the rail line it supported to continue operating. CGS proposed to fix and stabilize the retaining wall by using the processes of soil nail installation and shotcrete application.
To begin the stabilization and initiate verification testing, sacrificial soil nails were installed. An initial two-inch thick layer of shotcrete was applied to provide a working surface for the soil nail construction. A drainage board and weep hole assembly were spaced three feet on center to provide drainage for the newly shotcreted wall. Due to a large portion of the wall collapsing (15′ x 13′ x 3′), shotcrete was applied before the soil nail installation. We needed to build this failed section to match the grade of the section that had not fallen. Six rows of soil nails were installed in a top-down construction with each nail being either 14 feet or 30 feet in length. The top several rows were shortened to avoid hitting a fiber optic line. Once these rows were complete, reinforcing steel rebar whalers were installed and a final layer of eight-inch thick shotcrete was applied.
A total 586.5 cubic yards of grout and 102 soil nails were installed. CGS used neat cement with approximate 28-day strength between 4,000 and 5,000 psi.