Construction
Construction
Cadent is an experienced and trusted operator of gas pipelines. We will bring our extensive expertise of constructing, operating and maintaining the existing gas network to this project.
The pipeline would be constructed predominantly using open trench techniques. Where it is not possible or practical to use open trench pipeline construction, trenchless crossing techniques will be used to cross existing infrastructure like roads, railways and waterways.
Once the Project has been constructed, the pipeline will be buried underground. Only the above ground infrastructure will remain visible at certain points along the route.
Open trenching
Open trench (or ‘open cut’) excavation is the most common method for installing underground pipelines, cables or other below ground infrastructure.
- Open trenching begins by marking out the total area within which construction work will take place.
- The area is surveyed and the appropriate environmental mitigations are installed around the working area to protect water ways, important environmental receptors and areas which require mitigations in how we construct the pipeline or HAGI.
- Topsoil is then carefully stripped and stored next to the pipeline route so it can be maintained. Meanwhile, the pipeline’s individual pipes are delivered in short lengths and placed on temporary supports. These short lengths of pipeline are welded together into longer sections called ‘strings’.
- Testing is completed on each weld and a full inspection report produced before the welds are coated.
- The pipeline trench is then dug, with excavated material stored separately from the already stripped topsoil.
- The pipeline ‘strings’ are then lowered into the trench using special vehicles called ‘side booms’ (pictured) or excavators and welded to the pipeline that’s already been laid.
- The trench is backfilled using the previously excavated material and the topsoil is replaced.
- The pipeline is then hydrotested (filled with water) to prove it is fit for operation. Rigorous checks are then undertaken prior to the pipeline being commissioned once the entire section is complete.
- Once the land above the pipeline has been fully reinstated it can be returned, as far as possible, to its previous use. We anticipate that open trenching will be the predominant technique we use to construct our underground pipeline.
- A short time after reinstatement it will not be possible to see where the pipeline was constructed, apart from pipeline marker posts installed at fence lines and boundaries to identify its presence.
Trenchless methods
(for roads, rivers, other utilities, and rail)
In some cases, for engineering and environmental reasons, open trench methods are not viable so trenchless methods will be considered.
We’ll need to use trenchless methods at various points along the pipeline route.
Auger boring
Auger boring can either be ‘cased’ or ‘uncased’. For cased auger boring, steel or concrete pipe sections are pushed along the crossing section and material is removed by the auger drill inserted into the pipe. Following installation of the casing pipe, the hydrogen pipe is inserted with insulators to insulate and centralise the pipe in the casing. For uncased auger boring the hydrogen pipe is inserted directly into the ground with no casing.
Direct pipe
Direct pipe can be applied to longer trenchless crossings. This technique is similar in its method and set up to micro-tunnelling (see below). However, the pipeline is installed directly into the ground behind the cutting / tunnelling machine, rather than the pipeline being installed inside another pipe tunnel.
Horizontal Directional Drilling (HDD)
HDD is typically used on long trenchless crossings. It requires an entry and exit pit on either side of the crossing. A hole is then drilled beneath the crossing and the hydrogen pipe pulled back through the drilled tunnel.
Micro-tunnelling
Micro-tunnelling is especially useful for laying pipelines beneath motorways, large roads, railway lines and other sensitive areas. A cutting tool / tunnelling machine provides the mechanical excavation, which is generally controlled remotely above ground. Individual tunnel pipes (not the hydrogen pipe) are installed behind the tunnel machine as it makes progress. Once the tunnel pipe is in place the hydrogen pipeline pipes are lowered into the tunnel where they follow the same strict quality inspections before being pushed into the tunnel pipe. This continues until the hydrogen pipe is fully inserted. Connecting sections of pipe are then installed to connect this tunnel section to the sections of pipeline either side. The tunnel is then filled with a grout between the outside of the hydrogen pipe and the inside of the tunnel pipe.
Work on roads
We will continue to survey the areas where construction may take place and work closely with local highway authorities to ensure that any roads we plan to use for construction are suitable and safe for all road users.
If the proposals are approved, we may carry out improvements to bring certain roads up to the required standard for construction traffic, for example small scale road widening. We may also use temporary traffic management measures, such as banksmen and temporary traffic lights.
Keep in touch
Register for updates
If you want to know more about H2East Pipeline: Humber to Nottinghamshire then please contact us.
You can also register your contact details with us if you would like to be kept informed about our project.