Site Investigation

Throughout 2016 and 2017, detailed design works will take place along the onshore cable route. These works will involve some site investigation campaigns and we have provided more detail on what each campaign will involve below.

Some of the equipment involved is also shown at the bottom of this page.

Full information on these individual topics is available by clicking on each of the headings, below.

Archaeology evaluation and Trial Trenching

General overview 

An Archaeological Trial Trenching campaign will investigate the full route of the onshore cable corridor, including the fields adjacent to the landfall location and the onshore Substation and Intermediate Electrical Compound sites.

These works are required to ensure any important archaeological sites are identified and protected in accordance with planning policy and the commitments in the Triton Knoll Development Consent Order.

Trial Trenching is a trench digging technique used to establish the presence, condition and date of any archaeological remains which may be present.

The process usually follows non-intrusive investigations, such as assessments of aerial photography, desk-based assessments and / or geophysical surveys. In the case of Triton Knoll, geophysical surveys supported by investigations of existing data have determined the location and number of trenches required

Latest Update

Work got underway on Monday, July 31, 2017. If you would like to know more about these investigations, please see our Q&A document which should answer most queries.

If you have any further questions or issues you’d like to raise, or would like to know more, please contact us either by phone on 0845 026 0562 or by email .

Geophysical Surveys (Geophys)

General Overview

Geophysical surveys (or ‘geophys’ for short) may use a number of different methods and sensing instruments to collect information about the physical properties of land so that features in the subsurface can be identified. Readings are collected in a systematic fashion over a site, often covering large areas quickly.

Instruments can be handheld, pushed on a cart or pulled across the ground. The type of equipment is selected depending on the target object and site conditions. The results of surveys can be used to reveal water table depths, unexploded ordnance, underground services such as drainage pipes, or archaeological remains. Large areas can be covered in a single day using portable equipment.

These surveys are non-intrusive in that the surface of the land is undisturbed. However, crops growing above a certain height may interfere with the operation of the equipment.

Trial Excavations (Trial Pits)

General Overview

Trial pit or trial trench excavations are carried out in order to study or sample the composition or structure of the subsurface, such as for pre-construction assessments or for archaeological investigations.  Compared with light-cable percussion drilling or window sampling, this method of work is relatively quick but results in a greater surface area for reinstatement.

Trial pits are usually carried out when the ground is able to stand temporarily unsupported. Temporary shoring can be employed, for example where there is water present in the excavation or where in-situ testing is required.

Prior to commencing survey works the test location is hand dug to 1.2m to check for any buried services or other hazards. Following this a mechanical excavator is usually appropriate for excavating trial pits or trenches. Hand tools may be employed where underground services are known to exist.

Cone Penetration Testing (CPT)

General Overview

Cone Penetration Testing (CPT) Rig
Cone Penetration Testing (CPT) Rig

Site investigation using the cable percussive boring technique may be required in close proximity to where the cable route crosses obstacles such as main drains, river and roads and trenchless crossings are required.

The cone penetration test (CPT) is a common in situ testing method used to determine the geotechnical engineering properties of soils and assessing subsurface stratigraphy. The test is also called, Dutch Cone test. Due to its simplicity and efficiency, the cone penetration test is one of the most commonly accepted and used in-situ testing methods in geotechnical investigation worldwide.

Cable Percussive Boring (Bore Holes)

General Overview

Site investigation use the cable percussive boring technique may be required in close proximity to where the cable route crosses obstacles such as main drains, river and roads and trenchless crossings are required.

Light-cable percussion drilling uses a mobile rig with a winch of between one to two tonne capacity driven by a diesel engine and a tripod derrick of about 7m height. The derrick folds down so that the rig can be towed by a four-wheel drive vehicle. In areas where there is restricted headroom or access limitations a demountable or low-headroom drilling rig can be used. This rig is brought to site in sections on a trailer and the equipment is re-assembled on site. In areas where ground conditions are soft or wet, a tracked vehicle may be utilised to reduce ground pressure and impacts on soils.