Retaining Wall Subgrade Reinforcement

Scope of Work

To stabilize a deteriorated ledge cut beside Maine Central Railroad's active tracks. The rock reinforcement enabled the construction of a 30 + foot retaining wall atop of the ledge cut. The structure expanded the hospital densely build out campus for further development.

Challenges

The hospital buildings were situated as close as 20 feet off of the top of the rock slope and created one-sided equipment access to the 700-foot long retaining wall subgrade. The sound rock surface was to be prepared in stepped benches prior to vertical reinforcement using 1' and 1.75' 150 ksi galvanized dowels. The project was built from the far end back, requiring alternating rock step excavation with doweling and still maintaining equipment access on the tight sliver of land. The design of the reinforcement also required isolation of the dowel heads from the footings to avoid point loading. This was achieved by counter sinking the assemblies in 12' rock sockets. After the sockets were backfilled with cement grout, you never know they were there.

Outcome

With a good plan and versatile drilling equipment, a job everyone expected to be completed in 7 mobilizations (100 feet at a time for access) was completed in half the mobilizations, keeping all trades more efficient.