Recently Ament Design was engaged by an educational institution to provide a topographic map of a concrete courtyard and adjoining walkway corridors. The resulting mapping was to be used for design of underground steam lines between two buildings on each side of the courtyard.
Standard topographic mapping provides horizontal and vertical locations of features on the surface and typically relies on surface utility infrastructure to map the approximate location of underground utilities. However, for this project, clash detection was very important to determine if the project was feasible. The courtyard / corridor contained water mains, electrical lines, gas mains and steamline tunnels, all of which needed to be verified with accurate elevations.
There are several different ways to verify depths of utilities. One involves core drilling the concrete and potholing the earthen areas to uncover the utilities. The downside of this activity is that it leaves multiple unwanted holes in the concrete with a muddy mess on the sidewalks and grassy areas. Ament was looking for the most cost efficient, least invasive manner to accurately locate the existing utilities.The client did not have as-built locations of the steam tunnels that were built as early as the 1940’s to the 1980’s, only a general idea of where they were, which would have also made drilling and potholing a more cumbersome process.
We were familiar with GPR (Ground Penetrating Radar) as a newer type of technology that allows a scan of the surface providing visual imaging of underground features. Depths of the objects can be marked on the surface along with the location of the object. The objects are marked and located via standard surveying equipment, then placed into a 3D CAD model.
Utilizing GPR, we were able to locate the top and edges of the tunnels. GPR also provided a depth to the top. The steamline tunnels are accessible in certain areas and with the assistance of the client’s facilities maintenance group, we were able to access the tunnel toperform additional measurements. These measurements provided checks against the data marked on the surface and allowed us to get an accurate depth of the tunnel as well.
In the end, Ament delivered a clash detection model that provided valuable information that was cost effective and non-destructive to the existing features in the courtyard. This is just one example of how GPR, combined with standard topographic methods, can be a cost-effective way of collecting subsurface data.