The installation of the replacement pipeline will follow good industry practice using established techniques. The most common technique will use open-cut trenches, but in some areas trenchless techniques will need to be used.
Due to the potential need to make small adjustments to the location of the pipeline to account for local ground conditions, it is not possible to determine in advance the precise position within the route where we will lay the pipeline. We will seek formal permission in our application for development consent to lay the pipeline within “Limits of Deviation”, which is effectively the same width as the working width of the route that we consulted on in autumn 2018.
In rural areas, it is likely that we will use open-cut trench installation. During installation, we will maintain access to public rights of way, protect livestock, and work with landowners to reduce or mitigate the impacts of installation on how they use the land, where possible. Roads in rural areas can be narrow and winding. We will carefully plan our vehicle movements and the transportation of materials to reduce the impact on local road users. Temporary road signs will also be installed to alert people to any road closures and other changes in the area.
In urban areas, we will use methods such as traffic management and trenchless installation to enable us to work within more constrained areas. We will work with local communities and authorities to agree how we can minimise the impacts on public access such as footpaths and public areas. Once installed, the replacement pipeline will be a quiet neighbour.
We will use trenchless crossings under motorways, A-roads and railway lines to reduce impacts on people’s journeys.
If we are successful in our application for development consent, we will work with the County Highways Authorities in Hampshire and Surrey in relation to appropriate traffic management plans. We will work with County Highways Authorities and local councils to communicate our plans ahead of installation to local communities.
On a temporary basis, we may need to use diversions and access roads, move pedestrian walkways and bus stops and, in some cases, close sections of road. Where we do need to close a road, this will be done for as short a time as possible to reduce impacts on local communities.
The most common technique for installation of the pipeline would be open-cut trenches, which are less than one metre wide. Although the pipeline is relatively small, with an internal diameter of about 30cm, the working width needed for safe installation using this technique is usually between 20 and 30 metres. The working width allows sufficient space for digging the trench, laying a pipe alongside the trench before installation, storing topsoil and sub-soil separately during installation and enabling access for construction vehicles. At times, we will need to use narrower working widths for short distances, for example in urban areas or where space is constrained.
At times, we will need to use trenchless techniques to install the pipeline, for example under railway lines, major roads and river beds. In these cases, we will use methods such as directional drilling or auger boring, which use a machine to drill or ‘bore’ a hole through the ground from one side of an obstruction, such as a railway line, to the other. Typically, a pit is dug at either end of the trenchless section from where the machinery can be located. Throughout the work, care is taken to prevent any movement of land. The replacement pipeline will not go under any existing homes, even where trenchless installation is used.
While trenchless techniques cause less disturbance at ground level, allowing roads and railways to remain open and rivers to continue flowing, more land may be temporarily required for pits for the drilling machinery relative to open-cut trench techniques. Depending on the length of the trenchless section, it may take longer to complete trenchless installation relative to an area where open-cut trench techniques are used. Furthermore, sections of the pipeline that are installed using trenchless crossings can largely be installed in a straight line. This means that only certain types of trenchless techniques can be used.