Investigating Coastal Stability

CC Ground Investigations Limited have recently been an integral part of the team delivering ground investigation data to investigate slope instability at Southend-on-Sea. Concept Engineering Consultants Ltd engaged CCGI to carryout multiple Geobor S rotary and cable percussion boreholes to investigate the ongoing cliff instability.

The Geological Setting

The British Geological Survey (BGS) indicated the site to be underlain by the London Clay Formation, with the majority of the site areas affected by landslides.

Why was a Ground Investigation Required?

Southend on Sea City Council had identified in their development plan the need to address the cliff instability, and for any instability to be investigated and addressed in any future developments. They summarise the issues as “The Thames Estuary frontage of the borough is backed by cliffs from the western boundary to Marine Parade in the east. The cliffs are often steeper than the natural stable gradient for the materials of which they are composed. As such there has been an on-going history of movement of the cliffs ranging from small scale slumping to major rotational and transitional movements, such as that seen below the Southend Bandstand in 2002. The cliffs, if not maintained, over a significant period of time, would naturally degrade to a stable profile which would continue to slump and move northwards. However, such a situation does not accord with the built environment of the borough and measures would need to be introduced to prevent and or reduce the movement or accommodate it. Before any significant works are to be undertaken it will be essential to monitor existing movement to identify the nature and extent of the problems that the cliffs present”.

The Solution

Southend on Sea City Council appointed Campbell Reith to provide consultancy services to address the issues of potential instability. Campbell Reith identified four high risk sites in the area and through open tender Concept Consultants were appointed as the main contractor for the ground investigation. Concept’s aim was to offer an integrated service to deliver a high-quality product, on time and on budget, upholding the values and principles of Southend-on-Sea City Council whilst also supporting and contributing to the local Community Engagement Plan and Local Area Engagement Plan.

To support Concept, CC Ground Investigation supplied two Geobor S rotary rigs and one cable percussion rig. The Geobor S rigs delivering boreholes to between 10 and 30m to identify shear surfaces and slip planes, and the cable percussion rig allowing targeted sampling using Class 1 UT100 samples. Installations for post investigation monitoring included vibrating wire piezometers , inclinometers or standpipes. A summary of the work is provided below:

Ground Investigation Summary:

No of Geobore S Rotary BoreholesNo of CP boreholesRotary Coring (M)CP Boring (m)No of inclinometers installedNo of Vibrating Wire Piezometers InstalledNo of Standpipes installed

CC Ground Investigations were delighted to be featured on the front page of Ground Engineering magazine in May 2023.

Further details of how CCGI carried out our part of the GI can be found on our case studies page.