Trenchless helps Virginia town avoid parking problems

Faced with replacing 500 feet of an outmoded, undersize, 8-inch sanitary sewer line with 10-inch pipe for increased carrying capacity in a heavily traveled commercial and residential a real Vienna, Va., turned to trenchless technology.

The existing sewer line, used to service about 300 residential units, ran beneath a commercial parking lot and connected to a 10-inch sanitary sewer located under a main arterial feeder for the area’s roadway system.

Originally, the plan was to open cut the parking lot to install replacement line. After investigation, however, it was determined that open excavation would pose a danger to existing building footers. Trenchless replacement also avoided disruption of parking and access to businesses located in the construction area.

The pipebursting method of rehabilitation was selected because it produces a larger line.

It also permitted upgrading to new continuous polyethylene piping that would improve flow characteristics and correct deficiencies such as cracked and deteriorated pipe and offset joints.

Miller Pipeline, Indianapolis, used a pipe splitter and hydraulically operated expansion head to break away the existing pipe, which is pushed into the surrounding soil. At the same time, new heavy-duty, high-density polyethylene pipe was pulled directly into the expanded annular space in a non-destructive process that eliminates shock damage to adjacent utilities. Additionally, the use of hydraulic power for installation equipment greatly reduces noise compared to traditional trenching or pneumatic-power pipebursting methods.

The corrosion-proof pipe was installed in continuous, fusion-welded sections, allowing placement in smooth, jointless lengths and eliminating the potential for future joint problems.

Because the main changed direction at a manhole, two entry excavations were required for insertion of a pipe splitter, expansion head and new pipe into the existing sewer line. Since the pipe to be replaced was a sanitary sewer line less than 14 inches in diameter, existing manholes were used as receiving areas for the pulling winch. Prior to installation, a closed circuit television camera was used to locate the three lateral lines that were connected to the existing line.

These laterals were excavated and disconnected just before installation of the new pipe and reconnected afterwards.

A total of 494 feet of pipe was installed in two pulls. One launch excavation was placed upstream and received through the manhole located where the line changed direction. The second excavation was placed just next to that manhole, and another manhole downstream was used as the second receiving area. A flow bypass line was used during installation of the new sewer.

Finally, the individual lateral connections were renewed and the installed line was inspected via television.