Technical Insights by Brian Lakin, PE
While our infrastructure continues to age and the cost of maintaining our assets skyrockets, it becomes imperative for owners and operators of our water, wastewater, and storm infrastructure to consider all available tools when determining how best to monitor the ongoing condition of their buried pipelines, tunnels, and facilities. It is also of the utmost importance that owners and operators understand the logistical and safety requirements necessary to complete a successful inspection program that yields results that are useful and contribute to the overall management of the asset.
Historically, an inspection has been conducted by a team of inspectors who are put into the tunnel or structure to directly observe existing conditions. The level of detail obtained from these inspection teams is tremendous. The trade-off to this, however, is multifaceted. Manual inspections require that safety precautions be taken, which can be quite extensive depending on the configuration of the facility to be inspected. Manual inspections also require that facilities be placed under restricted operation or removed from operation entirely. This can include the complete unwatering of a structure, which is time consuming and could require that backup systems be put into operation that are not typically used for extended time periods. It could also place unknown structural stress on a facility that isn’t normally unwatered, adding a degree of risk for an owner.
Inspections using remotely operated vehicles (ROVs) offer some attractive alternatives. ROVs are underwater vehicles that can be controlled from the surface through an attached cable (umbilical) and flown into a watered structure to take still photos, video, and sonar data. An ROV control station provides power and control to the ROV and stores this information, as well as other collected data on computers for later use and analysis. Multiple monitors are provided for both pilot and engineer to monitor the inspection in real-time. Safety requirements for ROV work are typically minimal. Mobilization and demobilization times are short when compared to manual inspections. That being said, ROV operations need to be carefully planned, and an understanding of the configuration of the target structure needs to be well understood prior to beginning any work so that one can plan for any operational constraints. This understanding will minimize the risk of the ROV or its umbilical getting caught on an obstruction within the structure.
A more relaxed definition of ROVs could include such developing technologies as aerial drones and self-guided robotics platforms, which are now becoming available. As with all technology, the capabilities of ROVs continue to grow. ROV data can now be used to create three-dimensional renderings of a tunnel or structure. These data can even be combined with photos to create composite depictions of a structure, which can then be compared to the results obtained from follow-up inspections. As the technology continues to change and computers get smaller and more powerful, the only restriction on what an ROV is capable of doing may be whether we can make a waterproof enclosure to house the equipment. Stay tuned for a future article on aerial inspections using drones.
McMillen Jacobs experts have completed many ROV inspections for municipal clients including the Great Hill Tunnel Rehabilitation Project in Connecticut. This project was the recipient of multiple engineering awards.