In March 2011, Pro-Pipe was contracted to participate in an unlined concrete sanitary sewer rehabilitation program for the wastewater collection utility authority for a city in New Mexico. This consisted of sliplining approximately 1,600 ft of 60-in. sanitary sewer and the cured-in-place (CIPP) of approximately 4,300 ft of 15- to 24-in. interceptor lines.

This project presented several challenges from the cleaning and preparation side of the sliplining process. The flows were not diverted and were between 60 and 80 percent full at the time of cleaning with 50 percent or more in debris volumes. To accomplish this, Pro-Pipe employed several techniques to assist in the cleaning and inspection side, which consisted of a 6-in. solids handling hydraulic submersible pump for material removal, sonar to identify where the debris volumes were and the amount along with conventional CCTV.

Pro-Pipe crews initiated cleaning on the upstream portion of the line and worked downstream. In order to do this, crews used access points that were to be used for insertion pits in the sliplining process, giving a large access point to the pipeline. The cones of the manholes were also removed to allow for access large enough to set the submersible pump in the manhole. The crews ran two nozzles designed for lines that have high flows and debris volumes with the twin Venturi nozzle along with a standard 14-tip bottom nozzle for removing silt and debris. Pro-Pipe used a step cleaning approach, working 50 to 100 ft at a time and progressing through the line in that fashion.

For the cleaning, crews operated a Vactor 2100 Series 80-gpm, 2,000 psi with a 15-yard debris tank and positive displacement vacuum system. Because of the depth of flow and debris volume, the truck was coupled with a Godwin 6-in. submersible solids handling hydraulic pump that was placed in the line and then pumped directly into the debris tank, by-passing the on-board vacuum system. During this process, it was also necessary to run a constant pump off of liquids through 6-in. discharge on the truck in order to keep the liquids off loaded and allow for room for the solids only. The tank was elevated, which resulted in the elimination of silt and sand to be discharged back into the system as it was deposited in the back of the truck and away from the pump off location. Utilizing this method, crews were very efficient at removing a tremendous amount of material per load and increasing productivity on the cleaning side.

It became immediately clear that the level of debris was substantial and flow velocities were slow, allowing for continuing settlement of material at all times. In addition to the silt and debris, hanging gaskets were dislodged and the reinforcing mesh was loose. The interior crown of the pipe had also degraded to the point of exposing the rebar, which was then falling into the flow. This created challenges, as the gaskets and mesh would have an impact on the solids pump when brought back through cleaning. It required constant monitoring and maintenance to free the pump’s impeller of the gaskets and mesh.

In addition to the initial cleaning, another pass was performed just prior to sliplining to ensure any material that had settled out between the time the initial cleaning was done until sliplining, would be removed.
For the CCTV portion, Pro-Pipe used a CUES OZII camera mounted on a boat platform, which was pulled through the line gaining inspection of the pipeline above the water line to identify areas that may present problems for the slip lining process such as hanging gaskets, broken pipe and to identify any pipe line alignment issues. To ensure crews were removing the debris necessary for the sliplining process, they used a Marine Electronics sonar unit, which was integrated into the CUES CCTV truck. This allowed the cleaning crews to identify the efficiency of the cleaning and aide in identifying areas where additional cleaning was necessary. This provided assurance to the slipline contractor that the line was ready for the sliplining process. Once the line was installed, two separate post-installation videos were performed — one prior to grouting and one after the grouting process had taken place. For this, a CUES OZII mounted on the boat was again used to obtain a visual inspection of the interior of the pipe.

The second portion of the project consisted of cleaning and video inspection of smaller diameter lines of 15 to 24 in. in preparation for the CIPP lining portion of the project process. This was a different process, as all cleaning could be completed while a full line bypass was running, eliminating the need for any additional pumps and utilizing the PD vacuum system. Again, a step cleaning method was used with the cleaning truck, working in conjunction with the CCTV truck with a tractor configuration guiding the cleaning crew through the line.

Once the line was clean, all lateral locations and clock positions were delivered to the lining contractor for reinstatement purposes along with video to allow for review prior to lining. Once the lining was completed, a second video was taken post installation to inspect the liner installation and confirm all laterals had been reinstated.

Dean Monk is a division manager at Pro-Pipe, which is headquartered in Mission Viejo, Calif.

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