Overview

Design and planning new construction requires detailed understanding of the presence and location of potentially conflicting subsurface structures. This case study shows GPR used in the subsurface utility mapping and engineering (SUM/SUE) process for a new transit corridor.

Complex site with typical mark-out of buried infrastructure.

Problem

The objective is to identify the location of all buried infrastructure, survey in its position, create digital map layers and identify conflicts with new construction plans.

GPR solution

SUM/SUE projects exploit a range of technologies for locating and mapping.  Readily identified metal pipes and cables are normally identified using electromagnetic cable detectors.  GPR is commonly used to define concrete and plastic pipes, abandoned pipes and cables as well as old foundations, ducts and chambers.
 

GPR cross-section showing multiple pipes and cables.




Field operator using GPS to geo-reference located marks.

The ASCE 38-02 standard for SUE provides guidance on the mapping deliverable. Steps entail reviewing records, verifying and detecting on site and possible excavation to expose for full identification and characterization.

GPR identified features are normally marked out with paint or markers in the surface.  The georeferenced location of the detected targets are recorded and entered into a database of GIS systems to render multiple layer digital maps.
 

 Typical digital map showing results of field mapping.
 

Results & Benefits

Using GPR as part of the SUE process is very common.  The benefits of GPR include:

• Simple deployment on site
• Immediate response visual with good depth estimate
• Detects wide variety of buried obstructions
• No need to be able to hook-up to the target
• Complements use of EM induction, magnetics and vacuum excavation