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Coastal cliff geohazards in weak rock: The UK Chalk cliffs of Sussex

By
R.N. Mortimore
R.N. Mortimore
1Applied Geology Research Unit, School of the Environment, University of Brighton, Brighton BN2 4GJ, UK
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J. Lawrence
J. Lawrence
1Applied Geology Research Unit, School of the Environment, University of Brighton, Brighton BN2 4GJ, UK
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D. Pope
D. Pope
1Applied Geology Research Unit, School of the Environment, University of Brighton, Brighton BN2 4GJ, UK
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A. Duperret
A. Duperret
2Laboratoire de Mécanique, Faculte des Sciences et Techniques, Université du Havre, 25 rue Phillipe Lebon, BP 540, 76058 Le Havre cedex, France
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A. Genter
A. Genter
3Bureau de Recherches Géologiques et Minieres (BRGM) BP 6009 - 45060 Orléans cedex, France
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Published:
January 01, 2004

Abstract

Geohazards related to chalk coastal cliffs from Eastbourne to Brighton, Sussex are described. An eight-fold hazard classification is introduced that recognizes the influence of chalk lithology, overlying sediments and weathering processes on location, magnitude and frequency of cliff collapses. Parts of the coast are characterized by cliffs of predominantly a single chalk formation (e.g. Seven Sisters) and other sections are more complex containing several Chalk formations (Beachy Head). Rock properties (intact dry density or porosity) and mass structure vary with each formation and control cliff failure mechanisms and scales of failures. The Holywell Nodular Chalk, New Pit Chalk and Newhaven Chalk formations are characterized by steeply inclined conjugate sets of joints which lead to predominantly plane and wedge failures. However, the dihedral angle of the shears, the fracture roughness and fill is different in each of these formations leading to different rock mass shear strengths. In contrast the Seaford and Culver Chalk formations are characterized by low-density chalks with predominantly clean, vertical joint sets, more closely spaced than in the other formations. Cliff failure types range from simple joint controlled conventional plane and wedge failures to complex cliff collapses and major rock falls (partial flow-slides) involving material failure as well as interaction with discontinuities. Other hazards, related to sediments capping the Chalk cliffs, include mud-slides and sandstone collapses at Newhaven, and progressive failure of Quaternary Head and other valley-fill deposits. Weathering, including the concentration of groundwater flow down dissolution pipes and primary discontinuities, is a major factor on rate

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Geological Society, London, Engineering Geology Special Publications

Coastal Chalk Cliff Instability

R. N. Mortimore
R. N. Mortimore
University of Brighton, UK
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A. Duperret
A. Duperret
Université du Havre, France
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Geological Society of London
Volume
20
ISBN electronic:
9781862393820
Publication date:
January 01, 2004

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