Wales & West Utilities, together with its long term contracting partners, have successfully replaced 850 metres of large diameter (16”) gas main with new 355mm P.E on a major through road in Bristol. This large scale project was part of the national 30 year gas mains replacement programme, which will provide a safe and dependable gas network for the future. The Live Mains Insertion technique (LMI), developed by Steve Vick International, was chosen to complete the project.
The LMI technique is a safe, fast and efficient method of replacing old cast iron mains with new P.E pipe – without interrupting customers’ gas supplies. The major benefits provided by LMI meant the technique was the obvious choice for Wales & West Utilities contract partner Morrison Utility Services, who sub-contracted Thompson Utilities to undertake this central Bristol scheme.
Wales & West Utilities Technical Engineering Manager, Paul Breakey confirmed that; “An overall saving of £60,000 was made by using LMI as an alternative to conventional replacement methods.’
The project took place on busy Whiteladies road, so minimising disruption for businesses, including the BBC broadcasting studios, was crucial. Accordingly consumers were provided with an uninterrupted gas supply throughout the insertion programme. This was delivered via the annular space between the old cast iron main and the new P.E pipe.
Traffic management was also an important consideration. Only one insertion pit was needed for all three pushes, which dramatically reduced the traffic management needed and therefore traffic hold-ups. This also reduced reinstatement costs and environmental impact.
Irrespective of the challenging location, the project was completed ahead of programme in just six weeks and within budget. Onsite support and consumables were provided by Steve Vick International.
Live Mains Insertion
Live Mains Insertion is similar to normal insertion of polyethylene pipe (PE) into an old cast iron main with one important difference. By using a special gland box and a live head on the PE, the old main is kept live throughout the insertion process and the new PE is gassed up to maintain supplies to customers.
Once insertion is complete, the main is kept live to supply customers with gas via the annular space until it is operationally convenient to transfer the services to the new PE main.
A further benefit of live mains insertion over dead is that only one excavation needs to be open during the insertion process, reducing traffic management requirements. Operators consider this a major consideration with the cost implications of the new Traffic Management Act.
Whiteladies road gas mains replacement project – May 2015
Only one trench was needed for the insertion of 850m of P.E pipe – a major advantage given the considerable vehicular and pedestrian traffic on Whiteladies road. Once the trenches were prepared, a bypass was set up to maintain customer’s gas supplies. Whiteladies road is a busy destination with shops, restaurants and offices. Preserving the flow of gas to these premises was of vital importance to the success of the project.
The insertion was achieved in three separate pushes – 243m, 436m and 171m.
The project involved the connection of 45 services – and would be carried out at a later date to suit the contractor and gas consumers – an important benefit for city centre commercial customers.