That could be a sink hole forming. I had one in my parking lot - opened it
up and it was large enough to swallow a car. 110 tons of large stone and a
new blacktop job looked good until they dynamited for a sewer line across
the street. Now hole is back and the city has no liability - limestone
county sink holes form w/o notice. David and Goliath fight coming.

"effi" wrote in message
...
"Andy Hill" wrote in message
...
Got a strange one here. In the past year, one section of my ~13 year
old
concrete driveway (roughly 10' square) has developed a couple of cracks
and
settled 1/4" - 1/2" in the center relative to the edges. By itself,
that
wasn't enough to really bother me (other than a "that's weird"), but
this
weekend I noticed that section actually had a noticeable "drumming"
sound
compared to the other parts of the driveway when I dribbled a basketball
on it.
Not only did that make me lose concentration during a cutthroat game of
"HORSE",
it also made me start worrying a bit.

Anyhow, there must be a bit of a hollow under the driveway in that area.
No
water, sewer, or sprinkler lines in the vicinity, so I don't think it's
water
erosion. Not sure how to go about addressing the problem, 'tho. Just
get a
mud-jacker out and cross my fingers, or are there other things that need
to be
investigated first?

if by mud jacker you mean a company that will pump some kind of material
under your slab to relevel it, supposedly those technologies are
affordable
and feasible

don't just cross your fingers, have someone who knows what they're doing
look at your situation if you don't fully understand it