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Love me tender

CONTRACTS

TEXAN UTILITY contractor LA Fuller & Sons took the plunge into directional drilling in a big way when it bid for the contract to replace most of the west Texas city of Plainview's ageing residential water pipes.

Although the firm has more than 20 years of experience in water utility work, the $4M (£2.5M) contract is its first using directional drilling. LA Fuller & Sons president J Mark Fuller said they had looked into trenchless technology before, but 'We were looking for a job that was large enough to justify the purchase of directional equipment.'

The firm chose a Ditch Witch JT2720 Mach 1 unit supported by a FM13 drilling fluid mixing system for the contract.

Most of the residential water mains in Plainview are two-inch (50mm) cast iron pipes which have become blocked from corrosion. Almost all must be replaced.

'The original plan was for most pipe to be installed by open-cut construction and to jack and bore pipe under driveways, ' said Plainview city engineer Sean Lanier.

'But after considering the extensive surface restoration that would be necessary, LA Fuller and Sons proposed using horizontal directional drilling.' More than 90% of the 62,500m of replacement PVC pipe is 102mm diameter and the rest is 150mm and 200mm diameter. The new route closely parallels the existing water mains and is installed block by block.

A pilot hole is bored through the clay and gravel ground using a 130mm Ditch Witch Tuff Bit. A backreamer is then fitted which pulls the pipe in behind it. Pipe is assembled in a string and pulled in; or where space is restricted, in 6m sections. Average daily drilling production is about 215m for the 102mm pipe.

'The only problems we have encountered are making tie-ins to our existing system, and that is because it is so old, ' said Lanier.

'Directional drilling has greatly reduced the impact of construction for the residents of Plainview. For the city, it has cut the amount of pavement replacement that would have been necessary if we were excavating to install the pipe.' Construction started in April and is due to take two years.

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