In 2015, the town of Southbury, CT needed repair services for four culverts ranging in size and shape. The worst culvert (displayed in the pictures) was originally a multi-plate CMP pipe arch. The bottom of the culvert was in such bad condition that you could stick your measuring tape down and not hit any earth subgrade for 16+ inches. In addition to invert degradation, there was noticeable shape movement as you looked along the bolt line in the ceiling.
The stream flow was eroding the surrounding fill and started to create potholes in the roadway above it. East Flat Hill road is a very steep, winding road and is a linking road between the center of town and the suburban area surrounding it. Shutting down the road would have required a large detour. Access was challenging.
In order to properly rehabilitate the structure, a solution called Tunnel Liner Plate was utilized. It can be brought into the host pipe in 1.5 foot sections and assembled within the host pipe. The annular space and the massive voids around the host pipe were then filled with lightweight cellular concrete.