RIFAS intrusive ground investigations

As with the non-intrusive surveys the majority of works will be carried out on private land, however there will be a requirement to carry out surveys in the public highway and Crosshouse car park. These works will help us to better understand the ground conditions in the local area and will enable us to further develop our proposals for the scheme.

What did the non-intrusive surveys show you?

In Autumn 2023 we undertook several non-intrusive Ground Penetrating Radar (GPR) surveys. These surveys used radar signals to detect anomalies underground including services and structures.

After reviewing the results of these GPR surveys we were able to identify more precise locations within the GPR survey areas where we would be able to undertake the intrusive surveys, whilst avoiding any such services or structures.

Ground Penetrating Radar

What will the intrusive surveys involve?

The intrusive surveys will involve use of Cone Penetration Tests (CPTs) and cable percussion boring.

Prior to CPT’s or boreholes being undertaken we will first hand dig inspection pits to locate any buried services and verify the findings of the non-intrusive survey works.

CPTs involve pushing a cone between 15-20m into the ground and measuring resistance to the cone. This will provide information on the soil and material below ground.

Boreholes of between 15 to 25m will be advanced using a cable percussion rig. Samples from these boreholes will be tested in a lab for their engineering properties and environmental purposes.

These surveys will enable us to gain the best possible information on local ground conditions, which in turn will influence the design of the flood defence.

Where will the intrusive surveys be taking place?

The intrusive ground investigation surveys will be undertaken on the same sites that the non-intrusive surveys were. As before this means they will mainly be undertaken on private land along the scheme frontage. Contact has been made with all landowners and leaseholders that will be directly affected.

There will also be surveys undertaken at Crosshouse car park and access to areas of the car park and slipways may be impacted for a short period.

Works compound location

To manage the works on a day-to-day basis we will have a compound set up at Crosshouse car park. This will mean there is less available parking spaces at this location, but the car park will still be open.

Who will carry out the surveys?

The works will be managed by VolkerStevin, supervising a subcontractor Socotec.

When will the surveys be taking place?

The ground investigations themselves will be taking place from Monday 8 January 2024 and are anticipated to be complete by early March 2024. Weekly monitoring of water samples across a selection of the borehole sites will then be required for a further four to five weeks once the ground investigations are complete.

Additional intrusive investigations may be required as the project progresses and more information will be made available on these in due course.

How will this impact me?

The majority of intrusive surveys are being carried out on private land and therefore it is anticipated there will be minimal disruption to the general public.

However, lane restrictions will be in place at four different points in the Northam and St Marys area from Monday 15 January, for approximately two weeks. These restrictions will take place between 8am and 6pm in order to enable our teams and their machinery to access some of the sites required for the ground investigations, more information on these restrictions can be found in the table below (Please note these dates are subject to change dependent on progress and favourable weather conditions).

Anticipated time period Restriction/closure details
Monday 15 January to Thursday 18 January and Wednesday 24 January to Friday 26 January Lane restriction in place on Belvidere Road between the roundabout with Britannia Road and the junction with Belvidere Terrace.
Monday 29 January Lane restriction in place on the Millbank Road/Belvidere Road.
Tuesday 30 January Lane restriction in place on the Belvidere Road at Rochester Street.
Friday 19 January and Monday 22 to Wednesday 24 January Lane restriction in place on Marine Parade between Melbourne Street and the roundabout of Chapel Road/Elm Street.

To minimise disruption to residents we are not intending to work after 6pm or across weekends; however, should we experience any delays then it may be necessary to work on Saturdays. We would like to take this opportunity to apologise in advance for any inconvenience or disruption this work may cause.

While the surveys are being carried out, it is anticipated that survey areas will be cordoned off, preventing access to anyone other than the Ground Investigation team. Prior to the start of the works, we may reserve the works area using ‘no-waiting’ cones; please do not park where you see these cones as we may need to remove vehicles which block access to our works.

Further Information

If you would like further information on the surveys or believe that you may be affected by the surveys but have yet to receive correspondence from the Project Team, please contact us at rifas@southampton.gov.uk.