The Municipality of Maple Ridge in British Columbia, Canada, commissioned a spe-cialty contractor to build a 9 m (29.5 ft)diameter culvert, incorporated in a mechanically stabilized earth (MSE) wall, to provide a street crossing for a stream. The culvert had been partly sunk into the stream bed to adapt to the site conditions. The MSE walls were a maxi-mum 8 m (26.3 ft) high above the ground and 70 m (230 ft) long. Figure 1 shows part of the North Face of the MSE wall.
The fill used in the construction of the MSE wall contained a fraction of fine dredged river sand. After construction, fine particles of the sand dried out and started to migrate through the galvanized metal screen that comprised part of the MSE wall. This resulted in voids at the surface of the MSE walls. The voids were a concern as they constituted a potential cause for future settlement of the sidewalks and asphalt pavement constructed between the MSE walls. The specialty contractor decided to remedy this situation by arresting the migrating fill before it came to its natural equilibrium, by refilling the surface voids and applying a shotcrete lining.
The design engineer recommended filling the voids with shotcrete and stabilizing the surface of the MSE walls with a permanent shotcrete lin-ing. The specifications called for the following procedures: