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Title: Engineering properties of chalk in relation to coastal cliff instability
Author: Lawrence, James A.
Awarding Body: University of Brighton
Current Institution: University of Brighton
Date of Award: 2007
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Chalk forms many hundreds of kilometers of European coastal cliffs particularly in the UK, France and Denmark. This thesis is an outcome of the PROTECT (PRediction Of The Erosion of Cliffed Terrains) Project, a European 56' Framework funded programme undertaken by the University of Brighton, BGS (British Geological Survey), BRGM (Bureau de Recherche Geologiques et Miniirres) and GEUS (Geological Survey of Denmark and Greenland) to study coastal chalk cliff instability in the UK, France and Denmark. Chalk coastal cliffs of north-west Europe are continually subjected to changes in stress caused by internal and external factors. This leads to fresh geological properties, features and materials becoming an active part of the cliff instability regime. The methods, types, volumes and mechanisms of collapses have been investigated, characterised and found to be dependent on the chalk formation, rock mass properties cliff face orientation and cliff height. This knowledge has been used to investigate the possibility of providing better ways of predicting when, where and how cliff instability will occur. To better understand the mechanisms involved in cliff instability and help predict imminent failure research sites were selected in England, France and Denmark in areas where geological investigation was possible and the experimental methods of instrumentation could be undertaken and analysed to provide the most useful data. The research programme set out to investigate: (i) the temporal aspects of movements in the cliffs leading to collapse (ii) the failure mechanisms. This required integrating the detailed engineering geology with the results from the geophysical techniques and the rock mechanics testing (iii) An additional part of the investigation was interpreting the evolution of the landscapes and how this contributes to cliff instability. The principal factors identified here as contributing to cliff collapse are: (i) the influence of the fracture network (ii) the material properties (iii) different types of failure (iv) long term relaxation of fractures in the top 20-25m of the chalk causing this section to be more predisposed to weathering and instability, than the lower part of the cliff (v) the range of chalk strengths and a salt water weakening effect identified. The results indicate that each of the techniques studied (geological/geotechnical fieldwork, geophysical investigation, site instrumentation, topographical survey, cliff stability analysis, laboratory testing and numerical modelling) is suited to a particular type of geology, but not to all the geological situations investigated, and best result and interpretation are obtained when all the data available is combined in a holistic model. Hence, the detailed engineering geology is an essential prerequisite to the interpretation of results and the application of the techniques. Geological study through out north-west Europe indicates the transferability of these results to any chalk section so long as the detailed geology is understood. The research has proved capable of predicting a cliff collapse prior to the event occurring.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available