Robots Going the Extra Mile in Deep Tunnel Sewer Inspection Technology
The Three-Ds of robotics are “Dirty, Dangerous and Dull,” meaning if something falls into these categories, it is typically a great application for robotics. Sewer infrastructure is obviously dirty, very dangerous and repeatedly dull, thus creating a perfect application for advanced robotics. In the case of a particular deep sewer tunnel in a major city sewer authority, a “Fourth-D” of robotics applies, “Difficult.”
When the Allegheny County Sanitary Authority (ALCOSAN) needed to inspect its deep tunnel system, difficult challenges were ahead in order to inspect the entire system. The ALCOSAN deep tunnel system (DTS) is a gravity sewer; however, during normal operations it runs in a constant surcharged state. The access shafts are exceptionally deep, some more than 100 ft spanning over two miles between some access shafts. To put that in perspective, that’s the equivalent of more than 43 football fields end to end.
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ALCOSAN, located in Pittsburgh, services 83 separate municipalities with a combined population of approximately 840,000 residents with plant treatment capability up to 250 MGD. The primary conveyance is through the 30 miles of the deep tunnel system that ALCOSAN operates. ALCOSAN is currently under a United States EPA mandated consent decree to reduce combined sewer overflows (CSOs) by 7 billion gallons by 2036. To reach this goal, the Authority will spend approximately $2 billion. Part of the consent decree is to better understand the conditions of the deep tunnel system.
The 30 miles of the DTS were constructed from 1956-1959 with diameters ranging from 24 to 126 in. using common methods for tunneling in coal mining.
There were numerous difficult challenges that needed to be overcome to inspect the DTS.
RedZone Robotics’ technology was used to inspect the DTS, inspecting many areas never seen since construction 60 years ago. Portions of the DTS were inspected over the past years, but with many gaps due to the previous limitations of the technology to be able to reach the mile-plus long distances and unique flow conditions and depth.
Most conventional inspection platforms are limited to less than 2,000 lf distances due to limitations on the tether and platform capabilities. ALCOSAN’s DTS access distances required technology to go six to ten times longer, in addition to the extreme depths and submerged state making it even more challenging. Sonar was the primary sensor used in the past and on this inspection, but the use of Multi-Sensor Inspection (MSI) technology was also used for the first time since the DTS was in operation.
Shawn McWilliams, ALCOSAN engineer and project manager noted, “Sonar was the primary sensor used since the DTS is mostly submerged, but the use of Multi-Sensor Inspection (MSI) technology-including Laser-was also used in certain areas, which gave ALCOSAN a chance to see and measure the conditions for the first time since the DTS has been in operation for over 60 years.”
RedZone technology was used to inspect the tunnel while in service, reaching in some cases more than 13,000 lf — nearly 2.5 miles — between access shafts while deploying to depth over 100 feet deep. Another restriction was scheduling and working around the Authority’s late night/early morning drawdown, which was also dependent on weather conditions.
“It’s definitely a unique and difficult system to inspect, and I have been involved in millions of feet of sewer inspections in hundreds of cities. ALCOSAN’s system operates with difficult and limited access and you need specialized robotic equipment to go the extended long distances,” says Redzone director of field operations Chuck Pulaski.
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RedZone engineers had to retrofit their MSI Profiler, a “drone-like” robotic technology, with on-board battery powered computer data collection pods that collect millions of data points in the field in an expedited manner that are then post-processed off-line with certified special reporting technicians to provide measurable data and reports to get the extended distances.
The data that was collected and processed established an updated baseline that ALCOSAN can use to determine the condition of the DTS, the amount of debris, and also the depth and locations of sediment so ALCOSAN can properly rank and prioritize the locations that may need future work or track changes over time. Sediment levels were recorded and adapted to a PACP-coding format to import directly into ALCOSAN’s InfoAsset Manager system.
The data collected and reported will help ALCOSAN better manage the EPA consent decree requirements and plan for the best use of resources based on facts and measurable data. The data will help ALCOSAN determine accurate sediment volumes and depths that will help in planning future cleaning and rehabilitation projects.
Additionally, the data will help in the next phase of where future access may be needed and what might be the best cleaning methods and technologies.
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The advancements on the robotic technology allowed ALCOSAN to get 95 percent coverage of the entire DTS and will help guide the direction of decision process.
ALCOSAN’s DTS changed the rules of pipeline robotics from 3Ds to the 4Ds and with the advancements of the technology, allowed what was before considered almost impossible to become deployable. A testimonial to robotics constantly pushing the limits and going beyond what it thought to be the limit and literally going the extra mile(s).
Sam Cancilla is vice president of business development at RedZone Robotics Inc.