THE INSTABILITY ANALYSIS OF CHALK CLIFFS OF THE BLANC NEZ CAPE (PAS-DE-CALAIS AREA)

Abstract eng:
The chalk cliffs of the Blanc Nez Cape located in the littoral fringe of the northern France, and on front of the Dover cliffs (England), are the seat of natural phenomena of erosion and collapses of various sizes. Several collapses were observed at the site of Escalles, and have destabilized the top of cliff by opening cracks there. Following an observation campaigns, an instrumentation was installed to measure the cracks opening. With these same devices, vertical displacements were evaluated. On other hand, the observations carried out on ground reveal a relationship between the cracks at the surface and the depth fracturing which is of tectonic origin. Our current study aims to check the various relationships between the surface movements and deep dynamics. So the acquisition of site data will enable us to elaborate an adequate collapse model which will take account simultaneously of ground conditions supporting the movements. We will present in this paper, the first results of the surface follow up reveal that relationships might exist between the variation of water table level and the fractures movements and between the latter and the quantity of rainfall. These relationships enable us to utter some assumptions to explain collapse occurrences.

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