- Q.I need to pour a
thickened-edge slab foundation for a two-story garage
apartment across a recently dug 2-foot-wide utility
trench. The backfill over the trench has subsided, and
I'm concerned that the foundation may sag and crack at
that point. Can I add rebar to the slab to span this
area, or is it better to mechanically compact the
trench area?
A.Jay Meunier
responds: If you're in doubt but don't plan to
have an engineer's compaction test, you should
probably do both. Run over the trench area with a
plate compactor, preferably, or at minimum a
jumping jack, and top up any depression that's left
with the clean stone that you spread under the
slab. Then, for added insurance, add rebar to the
slab where it crosses the trench area. Use 1/2-inch
or 5/8-inch rod, placed perpendicular across the
trench and spaced 12 inches on-center. Cut the
rebar so you have at least 1 to 2 feet of length
over the undisturbed soil on both sides of the
utility trench.
Jay Meunier was formerly owner and operator
of a residential concrete business. He is now an
estimator for Pizzagalli Construction in
Burlington, Vt.