- ENGINEERING INFO
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Planning for the future, Norwich Public Utilities (NPU) recently decided to build a new one million gallon, pre-stressed concrete water storage tank. The storage tank would be fed by an existing 3,500-foot, 30-inch transmission main coming directly from the Deep River Reservoir Water Treatment Plant. The 30-inch cast iron transmission main, installed in the late 1920s through a wetlands area, had been a reliable pipeline for close to 90 years until it finally began to show signs of deterioration from years of operation and challenging soil conditions.
Because the new tank would be fed by a single source, NPU contracted with Tata & Howard Engineering (T&H) to assess the cast iron water main and make recommendations on how to ensure reliability of the pipeline for the future. Installed in environmentally sensitive wetlands, digging and replacing the 30-inch cast iron main would have been very difficult to permit and install via traditional open-cut construction. T&H decided that trenchless repair was the most cost-effective and least intrusive approach to rehabilitate the main. After reviewing and considering various materials and installation techniques, T&H recommended sliplining the existing cast iron water main with 24-inch Fusible C-905® pipe to provide NPU the most cost-effective solution while still meeting the system flow requirements.
“Coordination and timing on the overall project proved to be very difficult. Fusion and sliplining the Fusible PVC® pipe was the smoothest operation of the entire project.” David Ebner, Heitkamp, Inc.
|Pipeline Details and Project Summary|
|Project:||Norwich Public Utilities Deep River Transmission Main Rehabilitation|
|Pipe Size:||24” DR25 Fusible C-905®|
|Owner:||Norwich Public Utilities|
|General Contractor:||Heitkamp, Inc.|
Fusible C-905® pipe was selected because it offered the most optimal combination of large internal diameter (ID) relative to outside diameter (OD), and high operating pressure rating compared with other thermoplastic pipe material options. The ID/OD relationship was necessary for NPU to meet the flow requirements from the Deep River Reservoir Water Treatment Plant.
Heitkamp, Inc. was selected as the contractor for the project based on its extensive experience with trenchless construction. Before decommissioning the 30-inch cast iron main, two large bypass lines were assembled, tied into the water treatment plant, and placed into operation.
Once the bypass lines were operational, Heitkamp began cleaning and video inspection of the cast iron main. In adherence with sliplining best practices, a 40-foot “proof” piece of Fusible C-905® pipe was pulled through the entire length of the transmission main prior to sliplining. Video inspection and pulling a proof piece provided assurance that the existing line had no obstructions or deflections that would prevent a successful slipline operation. Additionally, the proof piece was inspected for scratches or gouging and showed only superficial scratching.
Heitkamp contracted with Underground Solutions, Inc. to provide 3,500 LF of Fusible C-905® pipe and fusion services. Heitkamp was able to stage and prepare the fusion and installation operations very quickly and efficiently. Using a “fuse-and-pull” installation technique minimized the construction footprint and maximized production and efficiency. Beautiful New England fall weather provided perfect conditions for pipe fusing operations. The entire 3,500 LF of pipe was fused and installed in just 11 days.