Q. What's a good way to set deck piers in shallow water?
A. Shane Bryant, P.E., an engineer in Tooele, Utah, responds: For a recent lakeside-deck project that involved placing 32 posts in 3 to 4 feet of water, we started by hand-digging out as much of the lake bed in the location of each footing as possible. Based on the 1,000-psf bearing capacity of the clay soil, we used lengths of 8-inch schedule-40 pipe as forms, driving them about 2 feet into the lake bed with a sledgehammer and a portable jackhammer and checking for plumb as we went with a torpedo level.
Once the pipe forms were in place, we used a torch to cut them off a few inches above the water level. Just before filling them with ready-mix delivered with a concrete pump, we suctioned out the water. Once the piers had cured, we used epoxy anchors to fasten galvanized post bases to their tops.
The remaining piers on shore were oversized to increase the deck's overall lateral stability.
