During the 1980s Round Rock had expanded its water infrastructure, installing over 160 kilometres of asbestos cement water lines and hundreds of kilometres of blue polybutyline service lines. Over the past five years Round Rock has been replacing the blue polybutyline service lines due to excessive line breaks.

During the course of replacing the water lines Round Rock Utility Engineer David Freireich said that they began to look at other issues in the water distribution system and decided to address the asbestos cement pipe water mains in older residential areas.

In 2007 Mr Freireich attended the Underground Construction Technology (UCT) conference in Houston to research pipe replacement techniques. “We are always looking for new and better ways to do things. I think UCT is where we first found out about the pre-chlorination process and wanted to learn more,” said Mr Freireich.

Replacing line in Round Rock

This was the first major water main replacement project in the town in over twenty years. The project involved upsizing over five kilometres of 6 inch and 8 inch asbestos cement pipe to 8 inch HDPE pipe in three older neighbourhoods affecting 415 homes.

The ground conditions consist of heavy clay and rocks that create a lot of heaving, shrinking and swelling of the soil. The contractors had a number of reservations about the rocky ground conditions. The whole line was under the footpath and the driveway.

Murphy Pipeline Contractors, of Jacksonville Florida, was the first contractor in the USA to begin using the pre-chlorinated pipe bursting process in 2000 and has replaced more than 46,500 metres to date. However this is the first time that the technique had been used in Texas.

Todd Grafenauer of Murphy Pipeline Contractor’s said “The main point that we emphasise to communities and engineers is that pre-chlorinated pipe bursting may not be the only solution to address the challenges of their ageing water infrastructure, as there are so many technologies available today.

“However, as communities are now discovering across North America, this process will play a substantial part in replacing more pipe every year in a more efficient, aesthetically pleasing and customer friendly way.”

The contractors estimated that the pre-chlorinated bursting method would be a 23 per cent cost saving over conventional methods such as open cut.

The HDPE pipe was prepared in a staging area near each neighbourhood. The process included butt-fusing the 12 metre sections with McElroy fusing equipment to form continuous 90 – 180 metre sections. The pipe was then pressure-tested, chlorinated, capped and sealed.

Murphy Pipeline Contractor’s increased their service crew to ensure they were only in front of a home for one day. President of Murphy Pipelines Andy Mayer said “Those open-cut boys can be in front of a house for weeks at a time.”

The interruption to water supply was limited to one day per home. Following written notification, the day prior to the burst Murphy Pipeline went door-to-door to inform residents of the temporary interruption.

The bursting crew excavated the launch and burst pits and decommissioned the old main. Once the pits were excavated, a HammerHead HB100 static bursting machine was set into place. Mr Mayer was the first contractor in the country to use the new 100 tonne HB 100 on a project and he helped design the machine. The Hammerhead HB100 is designed to replace potable water, sewer and gas lines as large as 16 inches and is compact enough to efficiently replace pipes as small as 3 inches.

Once the HB100 was set into place, the bursting crew began the rod payout procedure while the pre-chlorinated pipe was pulled into position near the launch pit. The bursting crew began by pulling back the pre-chlorinated pipe using a 10 inch bursting head and a ductile slitter to shatter the old cement line. By midday the new 8 inch HDPE main was in place. The service connection crew then began attaching the new service lines to the main using mechanical service saddle.

Mr Mayer said “Most communities believe that you have to fuse the service saddle to the main when using HDPE pipe. This is a misconception, we’re using a standard mechanical service saddle that you would use on PVC pipes, as well as DI fittings to make connections to valves, tee’s and crosses.”

A particular challenge of the project was the discovery that none of the original AC pipe was restrained. When the contractor attempted to re-energise the lines, they blew out joints further up the line. To overcome this they worked from valve to valve, capped off as they went and tied the whole system back together at the end of the project.

Future projects

Mr Freireich said that Round Rock is a different kind of city to most. “The city relies on the technical staff to make the decisions and has always been willing to try new products and processes.

“We foresee doing this over a period of several years,” said Me Freireich, “the town has also dedicating up to a million dollars a year to replace the AC pipe in areas that feature clay and rocky ground conditions.”

Mr Mayer concluded that pre-chlorinated pipe bursting is a great technology, “once communities fully understand they see how easy it is to install pipe and get customers back in service in a day.”