Summary
Most unstable slopes in the London Clay of south Essex are situated in areas where the overlying Claygate Beds are present. The Claygate Beds contain layers of sand which discharge groundwater that softens the underlying London Clay, thereby inducing instability.
Plasticity indices are lowest in the upper part of the London Clay, in which most instability occurs.
Where the Claygate Beds are absent, slopes on the London Clay are locally stable at slightly steeper angles, or unstable as a result of oversteepening by rivers. In a few areas, slopes are unstable below hilltops capped by Bagshot Beds.
Résumé
Les pentes d’argile de Londres les plus instables dans l’Essex méridional sont situées dans les régions où les couches de Claygate sus-jacentes sont présentes. Les couches de Claygate comprennent des niveaux de sable qui drainent l’eau souter-raine; celle-ci amollit l’argile de Londres sous-jacente et provoque l’instabilité.
Les indices de plasticité sont les plus bas dans la partie supérieure de l’argile de Londres, où se trouve la plus grande instabilité.
Là où les couches de Claygate sont absentes, les pentes d’argile de Londres sont localement stables pour des angles légèrement plus escarpés, ou instables aux endroits où l’action des cours d’eau les a rendues trop escarpées. Dans quelques régions, les pentes sont instables lorsque le sommet des collines est constitué par les couches de Bagshot.
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Denness, B., Riddolls, B.W. The influence of geological factors on slope stability in the London clay of south Essex, England. Bulletin of the International Association of Engineering Geology 13, 37–40 (1976). https://doi.org/10.1007/BF02634756
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DOI: https://doi.org/10.1007/BF02634756