California city planned installation of a new water line with the alignment crossing several busy intersections. Extensive buried infrastructure existed beneath the intersections but the accuracy of existing as-built drawings was in question.
To verify the drawings and obtain the precise position and depth of these utilities to plan the water line route, the City used the SUE (Subsurface Utility Engineering) process. SUE is an ASCE standard practice designed for gathering accurate utility location information to reduce the risk of damages and minimize unplanned redesigns during construction.
SUE level B calls for use of geophysical methods to verify the horizontal and vertical positions of buried utilities. Knowing that ground penetrating radar (GPR) could locate metallic, non-metallic and abandoned utilities, the city’s project team contacted Sensors & Software for a product demonstration.
Using GPR, the City obtained the information needed to design their new water line installation to avoid existing utilities. This approach not only prevented possible costly damage to existing infrastructure, but it also allowed optimization of the new installation with minimized costs and surface disruptions.
An LMX200™ GPR system was used for this trial. The LMX200™ is a professional level GPR system that provides for both real-time and post-survey display and analysis of buried targets.
Operators can add interpretations to the LMX200™ screen in real-time, and download the data from the unit; using an integrated GPS (global positioning system), interpretations are quickly transferred to engineering reports and geo-referenced digital maps ready for integration into CAD and GIS systems. This seamless information flow makes the LMX200™ GPR system ideal for use in SUE; information collected in the field is used for design or updating existing drawings.
The city's project team collected test data in the middle of an intersection; this required traffic control for safe access to the area. Three parallel lines of data were collected in Line Scan mode starting from the same base line. GPR targets were marked out in real-time using field interpretations (color-coded dots placed at the apex of the hyperbolas (inverted V's) on the screen) with associated position and depth information.
Data were downloaded into the EKKO_Project™ software, Sensors & Software's unique PC software used to organize and process collected data, as well as generate reports, output data in various third party system file formats. Since a GPS system was integrated with the GPR, the MapView window of EKKO_Project™ displays the path travelled, as well as the field interpretations. This information can be overlaid on a site image to help provide the perspective of where the data were collected and correlated with ancillary site data and surface features; in this case a Google Earth™ image was used. Using MapView, the user can quickly see the spatial relationship of GPR targets and use the long linear character of pipe and cable features to help classify the target types. (Figure 2).
Using the LineView module in EKKO_Project™, multiple GPR lines are easily be viewed at the same time. In this case, line 2 and 3 were displayed horizontally to enable comparison of responses. This allows the user to confirm that hyperbolas at the adjacent positions have a similar shape and depth. Combined with the MapView image shown above, it is clear that all features show up on both lines and are indeed linear targets running through the intersection.
The interpretation information can also be viewed in Google Earth™, exported into CAD drawings or output directly from the GPR as a CSV file with complete depth and geo-referenced position information. Using EKKO_Project™, screen images were quickly captured and inserted into a PDF document called the GPR summary Report, allowing instant results to be shared from each intersection investigated.
This case example shows how GPR can be deployed rapidly and provide high quality data; following a standard workflow results in high quality, Level B SUE outcomes. Using GPR, the City obtained the information needed to design their new water line installation to avoid existing utilities. This approach not only prevented possible costly damage to existing infrastructure, but it also allowed optimization of the new installation with minimized costs and surface disruptions. Further, the digital records are available for future projects in the same area. Incorporating the LMX200™ to carry out SUE for the city’s water line installation provided many benefits and the approach will be an integral component of future City projects.
Click here to learn more about LMX200™ Ground Penetrating Radar.
