Massachusetts Rehab: Pipe Bursting Used to Replace Collapsed Sewer Line in Westborough
The Town of Westborough, Mass., with its total population of approximately 20,000 people, is located West of Boston and like many utilities has buried infrastructure made of varying sizes, types and conditions and accepts sewerage from nearby towns.
In March, a segment of an existing 15-in., RCP sanitary sewer collapsed, causing a costly emergency repair and bypass. During that time, excavation was necessary to expose and restore flow. As that emergency repair was being performed, it was determined that there would be a high probability of future failure, specifically the emergency repair crew had issues finding solid enough pipe to make terminating connections to. The RCP pipe segment on its upstream end has a sanitary sewer forced main coming from the nearby town of Hopkington, Mass. The sections of RCP had severe H2S degradation at the crown with hanging gaskets that were apparent during a CCTV inspection performed following NASSCO PACP standards. Pre-cleaning was limited as further pipe failures were a severe concern until the bypass was in place. The emergency by-pass system was installed and left in operation until a risk evaluation and construction plan could be implemented to replace or rehabilitate the failing pipe located under a heavily traveled local roadway serving residential and commercial areas of the City.
The Town of Westborough and engineering firm AECOM issued for public bid a pipeline replacement project specifying pipe bursting of the existing 15-in. RCP and installing a new 16-in., HDPE SDR 17 IPS pipe and in turn awarded the Flanders Road Sewer Rehabilitation project in May. Pipe bursting was specified in the contract documents due to the high traffic volume in the area, including a Cumberland Farms warehouse seeing dozens of freight shipments in and out daily. Maintaining access to this site was instrumental to the projects overall success. Also the commuter route being a highly traveled one during the morning and afternoon work commute drove the project toward a process that would allow for an expedited construction schedule to keep social disruption to a minimum.
A total of 1,025 ft of 15-in., RCP replacement was awarded to the general contractor. Ted Berry Co. Inc. was hired as a sub-contractor to perform the HDPE pipe fusion and pipe bursting installation.
Pipe bursting is the only trenchless rehabilitation or renewal method that allows an existing pipe to be replaced with a new pipe of the same or larger inner diameter and would be able to reduce the excavation on the project by nearly 90 percent, as well as dramatically reduce the construction schedule and possible damage to nearby wetlands areas and local business. The IPBA Classification systems takes into consideration factors that contribute to the complexity of an installation and recommends proven experience in projects of similar scope and class, due to the size of pipe and length of proposed installations the project was determined to be a Class B pipe burst. The consulting engineer required proof of experience of projects of similar size and nature, which Ted Berry Co. was easily able to satisfy.
Design considerations evolve from many factors including but not limited to ground conditions, groundwater conditions, degree of upsizing required, construction and depth of the existing pipeline, adjacent utilities, etc. Based on these and other logistical issues of the project the Ted Berry Co. team proposed a pipe bursting plan to the general contractor that would utilize the pneumatic pipe bursting process. Localized excavation would be required to allow the new HDPE pipe to enter the ground as the bursting head and pneumatic tool would be inserted into the existing pipe. These pits, as well as termination pits that would allow the bursting head to be retrieved at the completion of a burst section were strategically located to minimize disruption and could be used to install new manholes that were specified on the project that has a internal epoxy coating to protect against future corrosion, additionally the new HDPE pipe would protect the pipeline from future internal corrosion.
In the pneumatic system, the bursting tool is a soil displacement hammer driven by compressed air. An expander is fitted to either the front or near the rear of the pneumatic soil displacement hammer. The pneumatic hammer assembly is launched into the host pipe via an insertion pit. The tool is connected to a constant tension winch located at the receiving point. The constant tension of the winch keeps the tool and expander in contact with the unbroken section of pipe and centered within the host pipe and when combined with the percussive power of the hammer helps maintain the hammer and expander inside the existing pipe. It cracks and breaks the existing pipe, with each stroke. The expander combined with the percussive action push the fragments and the surrounding soil away providing space for the new pipe.
Bursting equipment utilized was a 20-Ton tracked dual capstan, constant tension, variable speed winch from TT technologies. A 14-in., Koloss Grundocrack hammer (92 in. long, 2,601 lbs, 220 strokes per minute at 706 cfm of air consumption) from TT did the lion’s share of the work coupled to a 900-cfm compressor.
Bursting operations lasted two weeks, completing the installation in three segments — 489 ft, 207 ft and a section crossing a boxed culvert of 129 ft. The tooling was arranged in a “rear-mount” configuration with the expander affixed to the rear flare of the Koloss. This configuration allows for the hammer body to act as a “pilot” to keep the bursting hammer centered in the host pipe while it was being burst. Additional blades were field-welded onto the rear-mounted expander to ensure clean cutting of the reinforcement wire in the RCP. The blades were also instrumental in cutting a 20-ft section of recently installed PVC that was placed on 3/13 during an emergency repair. Without blades, a segment of PVC in a section of RCP can sometimes want to “ride” the expander, with the blades the PVC cut easily and stayed in place. Recent repairs can at times be problematic while bursting if not properly compacted, as loose soil can encourage the repair to “telescope” into the next pipe segment instead of bursting.
The pipe bursting project went on schedule and was completed in its entirety in three weeks, including six new epoxy-coated manholes and numerous service laterals needing reconnection with Inserta-Tees. Additional pump station work and meter calibration was performed once the mainline pipe was completed.
The Ted Berry Co. Inc. is an industry leader in pipe bursting. No company in New England owns and operates as much static or pneumatic pipe bursting equipment as the Ted Berry Co. Inc., which is also actively involved in industry associations such as International Pipe Bursting Association and the Northeast Trenchless Association. The Ted Berry Co. Inc. also provides additional trenchless pipe rehabilitation and replacement, HDPE polyfusion services, internal pipeline cleaning, pigging, robotic CCTV inspection with a full staff of PACP operators, utility locating, hydro-excavation, industrial vacuuming and hydro-blasting services.
Shawn Ready is trenchless technologies service group manager and senior project manager at the Ted Berry Co., Livermore, Maine.