Effect of groundwater and sea weathering cycles on the strength of chalk rock from unstable coastal cliffs of NW France

International audienceThe aim of this paper is to evaluate the role of groundwater and sea weathering on the strength of the chalk rocks exposed on the coastline of the English Channel in Normandy, NW France. We present a study of the rock strength variations of three representative chalk units (Lewes Chalk, Seaford Chalk and Newhaven Chalk) exposed at various locations on the coastal chalk cliffs. The combination of UCS tests and SEM observations have been used (1) on dry natural chalk samples, (2) on chalk samples at various moisture contents, (3) on dry chalk samples submitted to a 10-day cycle of alternating wetting and drying by distilled water and by sea water. Dry chalk samples show low UCS strength (3.46-4 MPa) indicative of very weak rocks. When chalk samples are submitted to progressive water wetting, they present a decrease of UCS strength and Young's modulus of 40% to 50%. This behaviour begins at low values of water content within the chalk, i.e., for a degree of water saturation ranging between 10% and 17%. When chalk samples are submitted to an artificial weathering cycle with distilled water, a decrease in strength is observed, whereas the Young's modulus increases. SEM observations indicate the occurrence of microcracks and particle aggregates in the sample. When chalk samples are submitted to an artificial weathering with sea water, the decrease of UCS strength and Young's modulus achieves a minimum. SEM observations indicate salt crystals within the chalk. On the coastal cliffs of NW France, weathering processes depend both on chalk lithology, which show a range of sensitivity to weathering and on the location of the chalk in the coastal area. Processes allied to the degree of weathering (e.g., salt crystallisation or fresh water disaggregation) differ in the chalk massif, on the cliff face and on the shore platform

The SIB Swiss Institute of Bioinformatics' resources: focus on curated databases

The SIB Swiss Institute of Bioinformatics (www.isb-sib.ch) provides world-class bioinformatics databases, software tools, services and training to the international life science community in academia and industry. These solutions allow life scientists to turn the exponentially growing amount of data into knowledge. Here, we provide an overview of SIB's resources and competence areas, with a strong focus on curated databases and SIB's most popular and widely used resources. In particular, SIB's Bioinformatics resource portal ExPASy features over 150 resources, including UniProtKB/Swiss-Prot, ENZYME, PROSITE, neXtProt, STRING, UniCarbKB, SugarBindDB, SwissRegulon, EPD, arrayMap, Bgee, SWISS-MODEL Repository, OMA, OrthoDB and other databases, which are briefly described in this article

Les plateformes rocheuses sous-marines de Normandie : un marqueur des paléo-rivages holocène et de l'accélération de l'érosion côtière des falaises de craie.

International audienc

Le risque naturel côtier sur la communauté d'agglomération du Havre (Haute-Normandie) (une évaluation des aléas)

LE HAVRE-BU Centrale (763512101) / SudocSudocFranceF

Coastal chalk cliff erosion: experimental investigation on the role of marine factors

International audienceIn this paper the marine factors of erosion contributing to the chalk cliffs located on either side of the English Channel are examined. From an analysis of the literature, the main physical phenomena determining the marine erosion of the shore platform and the foot of the cliff are considered. Field observations of the coastal chalk cliff show that the vertical erosion of the shore platform does not appear to be the main cause of cliff erosion, which is mainly governed by cliff collapse processes. To estimate the impact of waves on the base of the cliff, experiments were carried out in a wave flume. The pressure due to the waves and the dissipation of waves were measured for three simple configurations of the boundary conditions between the cliff and the sea. The pressure never exceeded the compressive strength of chalk rock. Nevertheless, pressure fluctuations due to periodic waves can induce a fatigue process within the fracture structures. The experimental results showed that the shingle by itself has a low effect on wave energy dissipation. The main effect of shingle is to reduce the water depth at the toe of the cliff. Furthermore, it is demonstrated that a lower water depth leads to a lower impact of the waves on the cliff

Cliff collapse hazards spatio-temporal modelling through GIS: From parameters determination to multi-scale approach

International audienc

Cliff Collapse Hazards Spatio-Temporal Modelling through GIS: from Parameters Determination to Multi-scale Approach

In this paper, we study the cliff collapses, using observations and in situ measures, along 120 km of the french chalk coastline in Upper-Normandy and Picardy. Cliff collapses occur inconsistently in time and space, in unpredictable way. A european scientific project ROCC (Risk Of Cliff Collapse) has been launched (1999-2002) in order to identify the critical parameters involved, to evaluate their impact and their interaction in mass movements. Cliff collapse process appears as a complex natural system, due to the large amount of parameters able to lead to a collapse. GIS approach has been used to allow an homogeneous cartography of each parameter reported on one layer each one, along a large surface of 120 km long coastline. The computation is decomposed in different steps which consist from the qualitative factors, to quantify them and to normalize them in space. On the basis of field measurements and data analysis, four types of geological information have been added to the GIS model and a first computation of hazard modelling has been proposed to design a collapse hazard sensitivity map, based on a elementary summation of the parameters. We now prospect to introduce a ruled-based systems, dealing with the complexity of the interaction of the local parameters. An interaction network must be defined to represent the spatial and semantic links between local parameters