Distribution of landslides and geotechnical properties within the Hampshire Basin

This paper outlines the sedimentary sequences and geotechnical properties of the Hampshire Basin, a basin of filled with 700 m of Palaeogene clays, silts, sands and limestones in southern England. The paper presents results so far of a study to synthesize relevant geological and geotechnical data and relate these to the nature of the landslides in this basin. The study has found that stratigraphic sequences and geotechnical properties vary considerably across the basin owing to basin morphology and depositional environments which are correspond to complex paleogeography and tectonic movements during the Tertiary. Over-consolidated clays with low residual shear strengths are extensive on moderately steep slopes and prone to landsliding, especially on over-steepened coastal sections. Landslides vary from mudflows through mudslides, rotational landslides and minor falls. Landslide characteristics are strongly influenced by lithology but gradient appears to be the controlling factor in many cases. The presences of weak strata (clays, lignite, laminated layers), the pre-existing shear surface, the lithological interface (sand overlying clay) play important roles to locally control the position of the shear surface and the type of movements. At a basin scale, inland landslides are associated with the development of drainage system during and since the Tertiary.