| Project Background |
| A 25-acre site located in eastern
Pennsylvania was investigated by Geo-Graf in an attempt
to delineate the extents and causes of several large
sinkholes that had been posing serious safety hazards to
site personnel and equipment. Area history indicated that
mining operations were once conducted on the site in the
late 1800's. Thus, abandoned mine shafts could also be
associated with the problem areas. |
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| Geo-Graf Investigation |
| The nonintrusive delineation techniques used by
Geo-Graf included: Ground Penetrating Radar (GPR),
Electromagnetics (EM), Radio Frequency (RF) and Magnetic
(MAG) geophysical instruments. The problem areas were
investigated, specifically the area that once contained a
12' diameter sinkhole that had been filled, but was in
the process of reoccurring. Geo-Graf conducted GPR
profiles over and surrounding the potential sinkhole
area. A large-diameter storm sewer was detected extending
tangentially to the sinkhole's subsurface boundary.
Geo-Graf concluded that this sewer pipe was cracked and
was allowing washout of subsoil under high pipe flow
conditions. Thus, instead of constantly filling the
potential sinkhole area, Geo-Graf recommended repair of
the cracked pipe which will subsequently eliminate the
future reoccurrence of this hazardous sinkhole. |
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| GPR Data Profile |
| Please Wait as
the image below loads. It is actual radar data of a
sinkhole collected by Geo-Graf engineers utilizing a 120
MHz GPR antenna |
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| Above: A GPR data profile over the
subsiding area. The air void interface as shown is
detectable via GPR since the radar impulse signal will
travel faster through air than through typical subsoil
conditions. Thus, a subsurface air void-subsoil interface
is created and can be delineated as shown. A storm sewer
was detected extending tangentially to the sinkhole area,
providing an avenue for subsoil washout. 120 MHz GPR
antenna system, edited from a 60ns range. |
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