The University of Southampton
University of Southampton Institutional Repository

A geomorphological and geotechnical investigation of the Roughlands Landslide Complex, Southwest Isle of Wight, UK

A geomorphological and geotechnical investigation of the Roughlands Landslide Complex, Southwest Isle of Wight, UK
A geomorphological and geotechnical investigation of the Roughlands Landslide Complex, Southwest Isle of Wight, UK
The Roughlands Landslide Complex, comprised of slumped blocks, minor scarps, debris slides and a wide graben, is one of the few contemporary landslides on the Isle of Wight to be without major geomorphological or geotechnical investigation. Furthermore, Roughlands poses a puzzle as to the origin and form of its basal shear surface. If compound coastal landslides in ancient marine sediments are typically controlled by a basal shear surface which is guided by a bedding parallel slide prone horizon, how is the shear surface accommodated into the ancient fluvial Wessex Formation, which is largely without such bedding features? The complex is hence subject to a thorough investigation. This includes a rigorous desk study, geomorphological survey, peg network monitoring campaign using DGPS, comprehensive geotechnical testing program, and the installation of two slip-indicators. Although largely stable during the summer, parts of the landslide complex are recorded moving at up to 6.5m yr-1 during the wet winter months, indicating a high sensitivity to groundwater variation. Following an appraisal of eight possible formation mechanisms, it is concluded that the basal shear surface which underlies the Roughlands Landslide Complex is most plausibly guided by the basal surface of a Cretaceous sheet flood deposit. Support for this comes from palaeo-environment interpretation, which reveals various mechanisms by which sheet floods could entrain swelling clays; the excessive recession at Roughlands in comparison to other parts of the southwest coastline, which indicates that geological dip (which varies about the Brighstone Anticline) is influential; the fossil record; relationships with newly recognized faults; and from field observations. Stability analyses find field mobilized shear strength is greater than laboratory determined residual shear strength, which may be in part due to entrained Cretaceous floodplain debris within the slide mass. The unpredictability of landslides on the Wessex Formation also identifies some geotechnical uncertainties which are a concern for all engineering works in ancient fluvial sediments.
Redshaw, Peter Graham
d78b6146-7ba9-4916-a148-934c63251871
Redshaw, Peter Graham
d78b6146-7ba9-4916-a148-934c63251871
Smethurst, Joel
8f30880b-af07-4cc5-a0fe-a73f3dc30ab5

(2015) A geomorphological and geotechnical investigation of the Roughlands Landslide Complex, Southwest Isle of Wight, UK. University of Southampton, Engineering and the Environment, Doctoral Thesis, 356pp.

Record type: Thesis (Doctoral)

Abstract

The Roughlands Landslide Complex, comprised of slumped blocks, minor scarps, debris slides and a wide graben, is one of the few contemporary landslides on the Isle of Wight to be without major geomorphological or geotechnical investigation. Furthermore, Roughlands poses a puzzle as to the origin and form of its basal shear surface. If compound coastal landslides in ancient marine sediments are typically controlled by a basal shear surface which is guided by a bedding parallel slide prone horizon, how is the shear surface accommodated into the ancient fluvial Wessex Formation, which is largely without such bedding features? The complex is hence subject to a thorough investigation. This includes a rigorous desk study, geomorphological survey, peg network monitoring campaign using DGPS, comprehensive geotechnical testing program, and the installation of two slip-indicators. Although largely stable during the summer, parts of the landslide complex are recorded moving at up to 6.5m yr-1 during the wet winter months, indicating a high sensitivity to groundwater variation. Following an appraisal of eight possible formation mechanisms, it is concluded that the basal shear surface which underlies the Roughlands Landslide Complex is most plausibly guided by the basal surface of a Cretaceous sheet flood deposit. Support for this comes from palaeo-environment interpretation, which reveals various mechanisms by which sheet floods could entrain swelling clays; the excessive recession at Roughlands in comparison to other parts of the southwest coastline, which indicates that geological dip (which varies about the Brighstone Anticline) is influential; the fossil record; relationships with newly recognized faults; and from field observations. Stability analyses find field mobilized shear strength is greater than laboratory determined residual shear strength, which may be in part due to entrained Cretaceous floodplain debris within the slide mass. The unpredictability of landslides on the Wessex Formation also identifies some geotechnical uncertainties which are a concern for all engineering works in ancient fluvial sediments.

PDF
REDSHAW 25124684 Thesis.pdf - Other
Download (23MB)

More information

Published date: June 2015
Organisations: University of Southampton, Infrastructure Group

Identifiers

Local EPrints ID: 386140
URI: http://eprints.soton.ac.uk/id/eprint/386140
PURE UUID: ecab9ffe-971f-4b01-b0f7-6c0a9eee3538

Catalogue record

Date deposited: 11 Feb 2016 14:43
Last modified: 17 Jul 2017 19:52

Export record

Download statistics

Downloads from ePrints over the past year. Other digital versions may also be available to download e.g. from the publisher's website.

View more statistics

Atom RSS 1.0 RSS 2.0

Contact ePrints Soton: eprints@soton.ac.uk

ePrints Soton supports OAI 2.0 with a base URL of http://eprints.soton.ac.uk/cgi/oai2

This repository has been built using EPrints software, developed at the University of Southampton, but available to everyone to use.

We use cookies to ensure that we give you the best experience on our website. If you continue without changing your settings, we will assume that you are happy to receive cookies on the University of Southampton website.

×