A sinkhole is a depression formed as the underlying bedrock is dissolved by groundwater
(usually limestone). Sometimes, surface water entering a crevice in the bedrock may be the
cause. Thus, sinkholes may form in low-lying areas where water is ponding. A hole will form,
at the top of the underground cavern that is dissolved, and the earth above the hole will
collapse into the hole.
Thus, a sinkhole often appears as a column when looking down the hole. This is the "throat"
of the sinkhole above the collapsed roof of the cavern. While most people think of sinkholes
as being huge obvious holes that can be seen by the news helicopter, most are only a couple
feet across and deep. The method of repair involves plugging the throat with larger stones or
a lean concrete mixture called "flowable fill". Once the throat is plugged, the hole is filled
in with smaller stone and earth.
Below is a typical construction detail for repairing sinkholes. This information was taken
from the Cumberland County Cooperative Extension website
(http://cumberland.extension.psu.edu/NResources/sinkhole.htm). This is only meant as a guide,
and not all components included may be necessary. We have provided a list of contractors below
who may be able to help you in devising a solution to repair your sinkhole.
You may wish to contact your homeowner's insurance to see if you have a claim, especially if
the sinkhole appears near a foundation or structure. Sinkhole insurance is also available
through most homeowner's insurance providers.
Brian P. O'Neill, PE
A sinkhole is best repaired by excavating to rock then building an aggregate filter in the
Step 1. Excavate the sinkhole down to rock if possible.
Step 2. Put a layer of large stones in the hole (cabbage size).
Step 3. Put a layer of smaller stones on top (fist size).
Step 4. Put a layer of gravel on top of the small stones.
Step 5. Cover the gravel with a geotextile fabric. This prevents the next layer (sand) from
being lost through the gravel.
Step 6. Cover the geotextile fabric with a layer of coarse sand.
Step 7. Fill the remainder of the hole with soil. This can be layered to match the existing
Ideally each layer is six inches to two feet thick. When solid rock is encountered near the
surface drop off the bottom layers (that is start with a smaller stone size) or use thinner
layers. It is important that the bottom layer be larger than the solution channel opening in the
bedrock. The objective is to provide an open path for percolating water so that it cannot carry
away soil and cause another sinkhole. The repair, as described, also provides good filtration of
South Middleton Township does not endorse the following firms as being better or worse than other firms which are not listed. We know these contractors are experienced in the area of sinkhole repair. Other contractors in the area are listed in the telephone directory's yellow pages under "Excavating", or for engineering consultation under "Engineers - Geotechnical":
John W Gleim Jr Inc
625 Hamilton St, Carlisle, PA 17013
Phone: (717) 243-7160
John F Walter Excavating
1 Mill Rd, Newville, PA 17241
Phone: (717) 776-3148
Mc Coy Brothers Inc
1514 Commerce Ave, Carlisle, PA 17013
Phone: (717) 238-4356
Dillsburg Septic & Excavating
516 Range End Rd, Dillsburg, PA 17019
Phone: (717) 432-9704