Mapping the Urban Underground
Urban rights-of-way provide unique challenges for utility detection and mapping. Not knowing the location of buried utilities can cause project delays, cost increases and other problems that increase overall project risk.
Issues associated with underground utilities are rapidly worsening due to the increasing density of underground infrastructure in major urban areas, including:
- utilities at different depths, made of different materials, joined in different ways
- uncertainty that the records received by the municipality or utilities are accurate, up-to-date and detailed enough to assist in accurate positioning
- quantity of intersections, where utility density is even higher and it is necessary to have vertical offsets in order to thread through new utilities.
Solutions for Underground Utility Mapping
Technologies used for underground utility mapping challenges can vary, however to be effective they should all follow the process outlined in the ASCE 38-02 – Standard Guideline for the Collection and Depiction of Existing Underground Utility Data. Having well-trained and equipped technicians is key, as well as having a single entity responsible for marking all known utilities and identifying unknown utilities. Using geophysical technology specifically designed to more accurately capture data in a dense environment can also provide precise location information for underground infrastructure. For example, the use of Multi-Channel Ground Penetrating Radar (MCGPR) can confirm and assist in positioning marks in congested areas and depict non-utility trench walls, horizontal extent of duct banks, and other areas of constructability anomalies important for the challenging project.
The Las Vegas Boulevard Water Main Improvements Utility Investigation is a recent project where Cardno is currently following ASCE 38-02 using a variety of technologies to provide comprehensive investigation results. Cardno is providing SUE (Quality Level B and A) services including records research, EM designating, vault scanning, and MCGPR along a 5.7 section of Las Vegas Boulevard (Vegas Strip). The continual high vehicle and pedestrian traffic on this site required extensive planning and permitting to minimize disruption and ensure safety, while capturing the complexity of the underground utility data. Along with traditional SUE methods, MCGPR added valuable information to the data.
The Quality Level B investigation of the North phase of the project, using traditional pipe and cable locators, identified utilities running in different alignments than what was shown in existing records. MCGPR, which was effective to a depth of approximately six feet in clay soil, confirmed some of the alignments identified during designating, and also found other unknown structures, providing critical information to the project team. Test holes leading to Quality level A data are planned in the next phase of the investigation.
Underground utilities in urban centers are aging, in unknown locations and in unknown condition. Comprehensive ASCE 38-02 compliant SUE investigations can help engineers, designers, and contractors make informed decisions that reduce risk.