| Project Background |
| A proposed DoT road-widening project included the construction of a retaining wall along the eastern edge of a road. In order to estimate possible construction costs, it was necessary to determine the extent of subsurface support materials required. Random core-borings along the length of the impacted roadway was the current method of cost estimation. Geo-Graf advocated the application of Ground Penetrating Radar (GPR) as a nonintrusive geophysical technique to delineate the entire route of the highway project. This procedure also incorporated ground-truthing borings as required. |
| Geo-Graf Investigation |
| After review and processing of the GPR data, solid
rock was detected along the entire 330' length of the
roadway at depths ranging from just under the roadway to
approximately 8'. The first 130' section appeared to
contain rock oriented differently than that of the middle
section (130' - 240'), which appeared to contain a rock
outcrop that extended up near the road surface. The
northern edge of this outcrop (140') was sharply defined
by GPR, suggesting a possible fault at this location. Three boring locations, provided by the DoT, at 52', 141', and 236' located solid rock at depths of 8', 4', and 3' respectively. The GPR-estimated depths at these locations correlated closely. However, the GPR data showed that the placement of any boring in the 140' area could result in a wide range of depths, as this location is on the steep northern outcrop slope. The 236' area also appeared to be a transitional location. |
| GPR Data Profile |
| Please Wait as the image below loads. It is actual radar data of a near-surface rock outcrop collected by Geo-Graf engineers utilizing a 120 MHz GPR antenna. |
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| Above: A GPR data profile showing a near-surface rock outcropping along the proposed highway construction area. 120 MHz GPR antenna system. |
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