Brought in to deal with 1,200m of steel gas main that was showing serious corrosion problems in Thalheim in east Germany, Dortmund contractor Speeck’s solution was a static burstlining unit.
Speeck was contracted by the Sudsachsen (South Saxony) Gas Company to replace the leaking 100mm diameter pipe which connects two separate villages.
An original tender specified open trenching. However, Speeck spelt out for the client a number of problems that could be expected using this method, including extensive and costly safety measures to be taken on the busy country road and costly shoring because of the nature of the soil.
Instead, the contractor suggested the Grundoburst 400 G unit which can replace a variety of pipe types from cast iron, to concrete, asbestos cement or clay. The unit pulls in new PVC or HD-PE pipes as it bursts its way through the old pipe.
The system comprises a robust cradle, a hydraulic power unit, so-called Quicklock rods and a variety of accessories. The rods are not threaded which saves time and the chance of thread damage. According to the maker experienced operators can carry out up to 150m or 200m of burst-lining per day.
But the pipe at Thalheim needed more than the static system, which is unsuitable for the tougher ductile iron and steel pipes found typically in gas and potable water applications. Addition of a 125mm roller blade unit attached to the rods when pulling pipes allowed the machine to split ductile iron and steel.
The machine cuts through the pipe using thrust forces up to 275kN. At minimum operating depth pull-back forces are up to 400kN.
The gas main had undergone settlement over the years and had been installed in slight bends. So the 1,200m total length was replaced in lengths of 100m, and a 80mm temporary bypass HDPE pipe put into operation. Fortunately there were no house connecting laterals and repair clamps were not likely to be found. Pits were reduced in number by using some to work in one direction first and then other with the rig turned 180°.
Preparations took about a week to create the required operating pits and carry out butt-fusion of the 125mm diameter safety line coated pipes, then Speeck’s team came in.
An extraordinary length of 380m of burst-lining was achieved on the first day and in a new record time of four operating days, the total of 1,200m of steel gas main was replaced.
The original tender specifications had included a total time requirement of four weeks for the pipe replacement project. Using this bursting rig and with a highly professional operating team the complete site with all auxiliary operations was terminated in just 18 days.
A challenge of a different sort faced Thrustbore Construction Company in the Saudi Arabian desert. Saudi’s variable sand, rock and often aggressive stony ground put the company’s newly-acquired directional drilling techniques through a severe test.
TCC, part of a construction group founded in 1953 by Sheikh Ali al Tamimi, added to its range of micro tunnelling, pipe jacking, auger boring, dewatering and sheet piling to win oil pipe work for the Saudi Arabian Oil Company (Saudi Aramco) which had approved TCC as one of its commercially registered contractors in 1998.
General manager of TCC Mustafa Kilic says he was also aware of the potential for pipe installations for the gas industry and for cable duct laying for the new network requirements of an integrated telephone and international communications system.
The company chose a Tracto-Technik Grundodrill 20S unit. First work was quite simple involving installation of two 4-way x 110mm cable ducts over a distance of 75m beneath a six-lane highway. But experience on this site at Half Moon Bay in Dhahran proved to be a useful insight into the ground conditions and bentonite mixing requirements.
The next job came after other construction companies had made abortive attempts to install 2 x 10″ steel casings at two separate locations beneath the main Dammam-Riyadh Highway. Soil conditions were described as shattered rock with a compressible strength of 60MPA that had so far beaten all other boring attempts.
TCC decided, in consultation with Tracto-Technik, that a Sharewell mud motor should be used for the job. Various 200mm to 350mm torque hole openers would be used with the thrust/pull back and torque, from the Grundodrill, which also has a copious mud flow capacity.
In fact during the mud drilling and subsequent hole opening stages, some 700 litre/minute of mud was recycled with a total bentonite consumption of 14 tonnes. To supply the required 280,000 litre of water, a convoy of water tankers had to be used on a round the clock basis to ensure continuous drilling.
The pilot bore was completed in a day. It dropped quite deep to clear a desalination water pipe on the nearside of the highway by at least 1m; achieved by boring at a depth of 7.5m. The extra depth meant extending the bore length from 240m to 270m.
Following the final hole opening, the steel liner had to be attached to the drill rig stems via a welded dome end cone attached to a 40t swivel to begin pipe installation.
However, after a steady final backreaming run of 141m, the steel pipe became jammed due to intrusion of loose rock into the preformed borehole. Several attempts to pull the jammed pipe back with a Caterpillar side boom failed.
The firm brought in its biggest pipehammer, a Grundoram Gigant from its Dammam depot to hammer the pipe from the end. This succeeded.
On completion the entire Grundodrill 20S, bentonite mixing system and recycling system was moved 40km down the highway and the second steel pipe was laid. On this occasion the bore distance was just a mere 192m and was completed in seven days.
TCC has since taken delivery of a second drill, a smaller type 10S.
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