Using the Live Mains Insertion (LMI) method, tRIIO, a joint venture owned by Skanska UK and Morrison Utility Services working on behalf of Cadent, Britain’s largest gas distribution company, recently inserted a new 355mm PE gas main 740 metres into an 18” underground cast iron pipe in one push. This exceptionally long insertion, given the diameter of the PE, was carried out in minimum time with very little disruption to property owners and road users.
The gas mains replacement project in Hounslow, West London, was carried out for Cadent’ by KLT Construction. Steve Vick International (SVI) supplied the equipment and consumable products used in the LMI process as well as providing a Pipe Handler and a Macaw Pipe Cracker to maximise efficiency.
The project involved replacing an ageing low pressure cast iron gas main in Vicarage Farm Road, Hounslow, which is a busy road lined with houses and businesses and linking with the A4. tRIIO decided to attempt the 740 metre push in one go to reduce time and disruption; for this, KLT used a SVI Pipe Handler, fitted with 355mm shells. The handler was attached to a JCB for the first 400m and a 14 tonne excavator for the remaining pipe.
The Pipe Handler allowed the 6 and 12 metre sticks of 355mm diameter PE to be safely manoeuvred and inserted without difficulty by the excavator operator, speeding up the entire operation.
Once the PE was inserted, a SVI Contract Service team carried out two foam-offs enabling the new main to be tested and commissioned. Further foam offs were executed to allow services to be connected. At this stage, SVI’s Large MACAW Pipe Cracker was attached to the excavator and used to crack the cast iron main swiftly and safely to expose a section of the inserted PE.
The mains renewal was completed in around five days with only a partial road closure for foam offs, test and connection. Customers’ supplies were only interrupted once when services were connected to the new main. Phil Walden of tRIIO says, “It’s been a very successful project with customers, pedestrians and road users not realising that 740m of main had been replaced. “The local Authorities were impressed with the way this was done and had no problem with extending the original notice past the original end date as they could see we were working as a team.
Live insertion means customer supplies stay live
Live Mains Insertion is similar to normal insertion of new PE pipe into an old low pressure cast iron main with one major benefit. By using a special gland box through which the PE is pushed, the old main is kept live throughout the insertion process so that customers’ supplies are not interrupted. Gas is provided via the annular space until it is operationally convenient to transfer the services to the new PE main. Excavation is kept to an absolute minimum which benefits the contractor, the environment and road users.
Steve Vick International is a world leader in developing techniques for ‘live’ insertion of cast iron gas mains. Literally thousands of miles of gas mains around the world have been inserted live since the technique was introduced in the 1980s.
Safer pipe handling and cracking
SVI’s range of Pipe Handlers are designed attach to the quick hitch or bucket pins of an excavator to grip the PE, position it in the excavation and insert the pipe. The entire operation is controlled from the cab, avoiding the need for operatives to handle the pipe or enter the trench. There are five models in the range – suitable for use with excavators from 1.5 tonnes upwards – handling pipe diameters from 40mm right up to 630mm.
MACAW Pipe Crackers are excavator attachments which allow safe, effective cracking of redundant cast iron mains from 8 to 24” diameter. They replace the traditional methods of breaking out a cast iron main using handheld tools such as a sledge hammers or ‘Podger bars’, which present health and safety risks.
tRIIO is a joint venture partnership between Morrison Utility Services and Skanska Construction UK.