Projects never before considered feasible are now part of a normal day in this industry, and to keep up with the demands of its clients UEA offers a variety of trenchless techniques in the various projects the company is involved in.

Federal Highway thrust boring

In February 2006, a B-Double fuel tanker drove into an embankment, rolled and emptied its load of fuel into the storm water drains running along the Federal Highway, 30 km north of Canberra.

The fuel ignited, causing serious damage to asbestos pipes, and potentially creating a huge environmental issue. While the majority of the pipes could be removed by conventional open trenching techniques, crossings of both the north and south bound carriageways had to be completed to remove 12 metres of 300 mm AC pipe under the north bound carriageway, 27 metres of 600 mm pipe under the south bound carriageway as well as 27 metres of 700 mm pipe under one of the exit roads. Under normal circumstances this would not be an issue but the asbestos regulations required UEA to ensure no dust or fibre particles entered the atmosphere.

To complete this work UEA decided to utilise its thrust boring equipment. On previous sewer contracts UEA had upsized existing mains using this type of boring equipment and installed a steel case into which a new carrier pipe was installed and grouted.

After further discussions with the concerned parties, including the RTA and EPA, it was decided to adopt this technique – the only constraint being that all excavated and augured material had to be removed, bagged and sealed before being sent to an approved asbestos tip site. All this work had to be undertaken by an approved asbestos removal company employed by the RTA.

The first bore was a 12 metre shot of 450 mm steel case, into which a 300 mm RCP would be installed. The launch pit (10 metres long x 3 metres wide) had to be totally encapsulated so the air quality could be monitored for asbestos particles. UEA used a water spray throughout the auger process to settle any dust. No asbestos was detected, which combined with the 45 degree heat was of some comfort to the removal crews!

All material was hand-shovelled into 44 gallon containers and sealed before removal from site. Drilling was completed within eight hours and the rig moved to the second site. UEA installed a 900 mm steel case while removing the existing 600 mm AC pipe. Due to the huge amount of material to be bagged, sealed and removed this bore (27 metres in total) took four days to complete before moving to the third site. This was a 700 mm AC pipe which required the manufacture of a new cutting head. UEA engaged its engineering division to manufacture the head at its new workshop in Goulburn. This bore also took four days in very high temperatures.

UEA was able to complete the works within a very tight time frame while meeting the stringent requirements of the EPA and RTA. For the duration of the works no asbestos dust entered the environment due to the diligence and expertise of the UEA crew. Combined with the ability to manufacture its own cutting heads and some lateral thinking, UEA was able to deliver a safe, cost effective removal process for the RTA.

Leura Bypass HDD

Barclay Mowlem had been contracted to install a tunnel as part of the Leura Bypass project in the Blue Mountains of NSW. The tunnel required lighting and fans, but conduits to supply the power were not available.

The integrity of the tunnel was a major issue - the sides were meshed and had been shot creted and the entry point for the conduits was eight metres below the finished surface - in solid sandstone. Trenching was therefore not an option.

UEA were contacted by Barclay Mowlem to investigate whether HDD was viable. The tight access made the bore near impossible for a conventional rock drill so UEA modified a 24 x 40 to undertake the work.

The client provided survey pegs every two metres along the bore path to monitor both line and level. The 24 x 40 was jacked up to the correct line and grade and using a Digitrak Eclipse Mark III the bore path was maintained for the duration of the pilot shot, enabling the exit point to be hit first time. The hole was reamed up to 450 mm diameter over a period of two days with a cherry picker used to change the reamers after each upsize was completed and the rods pushed back out to the face of the tunnel. Using the combination of the cherry picker, a franner crane and a 25 tonne excavator, the 4 x 140 mm PE electrical conduits were attached and pulled into place.

UEA’s lateral thinking when confronted with this unusual problem enabled a swift cost effective installation that ensured the integrity of the tunnel while minimising the disruption to the construction program.

Pipe bursting in Canberra

Like any other Australian city Canberra is growing. New sub-divisions are putting pressure on the old infrastructure, in particular the capacity of the sewer mains, and deterioration of the existing vitreous clay pipes has also led to extensive root ingress.

Replacing these assets without creating environmental issues posed a serious problem. Many of the surrounding trees have a significant heritage value and a number of the sewer lines are buried up to five metres deep backyards, with various access difficulties. Bearing these factors in mind, as well as surface structures placed on top of mains, and Canberra’s notorious ground conditions - dry, compacted clays that do not lend them selves to expansion easily - ActewAGL decided to adopt pipe bursting as its preferred option of rehabilitation.

ActewAGL has previously engaged UEA to undertake a significant portion of its sewer replacement program. The majority of the lines are 150 mm size for size replacements, with occasional upsizing project also completed. UEA employs a number of crews to undertake this work, combined with sub-contractors due to the scale of the program and tight timeframes.

A combination of pneumatic and hydraulic bursting techniques has been adopted, depending on individual site restrictions. Discussions with controlling authorities to determine the best approach are common place and no single technique offers the perfect answer to the renewal problem. UEA and its sub contractors use Tracto-Technik equipment in most cases as this has been found to be the most reliable and best performing equipment in the harsh ground conditions. In some cases the pipe turns to dust as expansion is limited.

Following CCTV and cleaning of the sewer lines, junction locations are marked out and excavated. ActewAGL require all junctions to be replaced, including the tie back to the property boundary - in some cases this can be up to 25 metres. Depending on depth, a launch and receipt pit are excavated. If the depth exceeds two metres, in most cases the TT 135 front mounted Grundo Crack is used to crack in to the manhole prepared by the operative. In all cases a polyethylene pipe is installed and junctions are electrofusion welded into place to ensure a completely sealed system that is guaranteed for 50 years with no annular gap or junction sealing issues. Once the pipe is installed all excavations are backfilled and restored with affected residents surprised at the minimal disruption caused. Over the past eight years over 40 km of sewer main has been replaced this way.

The diverse range of equipment and techniques offered by UEA has enabled ActewAGL to maintain its sewer system with minimal disruption to the customer, the environment and its network. Over the years UEA has used HDD, lining, thrust boring and various bursting techniques to provide cost effective solutions for the client.