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Georgia bursts with opportunities

TRENCHLESS TECHNOLOGY

A MAJOR sewer and water system renewal scheme is under way in Dalton, 145km north of Atlanta in Georgia, USA.

In response to an Environmental Protection Agency order, the city has replaced its wastewater treatment facility and has let a $1.2M (£750,000) contract to replace 3.5km of crumbling clay sewers.

Dalton Utilities, which operates the local gas, water, electrical and wastewater services, estimates the sewer system to be nearly 60 years old.

Most of it is at the base of a hilly ridge, so rainwater runs almost directly into it. The cracking, collapsing pipe means the system has become vulnerable to this runoff.

'It was obvious that the infiltration and inflow was severe after a storm, ' said Steve Bratton, wastewater collection systems manager for Dalton Utilities.

'The line was full and had clear water running through it.

Increased flow at the sewage treatment facility is a strong indicator that the lines are in need of repair or replacement.' Directional drilling firm Southeast Pipeline Construction of Jasper, Georgia was contracted to carry out pipe bursting replacement work on about 30% of the project. Its work began in June 2001 and was due for completion as GE went to press.

The firm's Tim Logan explained that it had been looking for a good opportunity to enter the pipe-bursting market.

'The market potential is huge, ' he said. 'The City of Atlanta has been talking about a major 'rebuild', and the City of Macon has too. We hope bursting can in time make up about 45% of our business.'

Southeast Pipeline chose the Vermeer Air Impactor for the work. The pneumatic 300mm pipe burster can be used with Vermeer D24x40A and D33x44 Navigator horizontal directional drills, so the company did not have to buy new equipment or retrain its staff. The device bursts through the old or damaged pipe while simultaneously pulling a new pipe into the compacted borehole.

There is little or no need for launch or reception pits as the bursting head is attached to the drill rod at the surface and then retrieved through a manhole, which also reduces the amount of surface damage. In urban or other restricted environments, the new pipe can be fused during the pipe-bursting process to further reduce disruption.

The air impactor is attached to the drill stem via a ball joint and locking sleeve. Air is delivered through the drill stem during pullback, producing impacts to the front of the tool body, in the same way as pneumatic tools but at a much higher frequency.

The impactor's active head design isolates the drill stem and the drill from impact force, which is comparable to a 200mm pneumatic tool operating at the industry standard pressure of 110psi (7.6bar). The tool is capable of operating at nearly double this, with increased levels of impact force attained at higher pressure, which may increase productivity in difficult ground.

The contractor used the impactor with a Vermeer D33x44 Navigator rig on a 85m run. The first 58m consisted of 300mm clay pipe, and the final 27m was 250mm. Both were replaced with 300mm HDPE pipe. The pipe was burst at an average rate of 0.9m per minute, with the entire job taking only 1.5 hours.

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