I live in a four-family building of townhomes, less than five years old.
The yard in front of the building has been sinking for some time, two or
three years. The sinking runs a line from one sewer clean-out valve at the
side of the building, down that side, turning a corner under the driveway
(which has cracked) into the yard to the next sewer cleanout valve, and out
from there. About three feet out from there is a small plum tree that his
now sitting in a sinkhole, it's probably 8 to 10" lower than the ground
around it. Besides this sinking, there is an area between that and the
homes, right in front of a decorative rockbed, which seems to be sinking in
the middle, forming almost a saucer-look to it. That part is almost exactly
behind the tree and about four or five feet back.
This has been noticed with concern by the lawn people, and most recently two
sewer companies who came to fix a backup, because they said it can be
indicative of a break in the sewer line. However, they dropped a camera
down the lines and found no breaks.
Both my neighbor and myself are getting concerned because it continues to
get worse. There are no basements, and when my carpet was pulled up
recently, I found a crack in the concrete extending from one end of the unit
to the other -- the builder tells me this is not a big deal, all concrete
buckles, and as long as the crack is going in one direction and not
spidering off, and as long as the crack is less than 1/4" wide and both
sides are level, it's nothing to be concerned about. The sidewalk has also
formed a horizontal crack, and the slabs are becoming quite uneven.
I realize that normal settling occurs after building, but this seems
extreme. Other than a sewer line break which has been ruled out, what could
cause ground sinking like this?