04-16-2010, 03:42 PM
I think what I would do is cut the bottom sheet rock on both sides below the roadbed. Then I would make a rectangular frame to bridge both holes, and use some aluminum angle screwed into the frame on each side to keep the frame from moving in either direction. That is undoubtedly NOT the way a pro carpenter would do it, but it seems like it would work, and once you put in the tunnel portals, the fix is hidden. The other method might be to make a "bridge" with plywood and the aluminum angle for the bottom of the holes. Then you install a tunnel liner from portal to portal to seal up the sides, but I'm not sure if a tunnel liner is as strong as the framing would be. By the way for that short distance to bridge the thickness of the wall, 1/8 inch luan door skin material would work fine.