Utility Tunnels Repaired with Fiber Reinforced Polymer (FRP)

Utility tunnels are concrete box girders that are widely used in major cities to house the various underground utility cables and pipes. Because they are always placed below grade, they are subject to moisture and in many cases the reinforcement in these structures corrodes. This could lead to potential failure and collapse of the tunnel.

The case presented here is such a tunnel located below the Arizona State Hospital grounds in Phoenix. In nearly all cases, the opening to the tunnel is very small, making it difficult to repair the structure with conventional approaches.

Carbon fabric was used to strengthen this structure. The fabric was saturated near the tunnel opening. Due to the extreme high temperatures in summer, the contractor provided a chilled room on the site to store the resins. A temporary canopy was also erected to shield the Saturation Machine and to prevent rapid setting of the saturating resin.

Saturated fabrics were passed into the tunnel through the manhole and were applied to all interior surfaces of the tunnel.

This slide shows the interior of the tunnel after the repair was completed. The pipes were temporarily covered with protective plastic sheets. The limited space inside the tunnel is clearly evident in this slide.

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