An engineering geomorphological investigation of hillslope stability in the Peak District of Derbyshire

Large-scale civil engineering works, planning and land-management in areas known to have a landslide problem require regional landslide susceptibility evaluation. The Matrix Assessment Approach (MAP) is introduced as a technique for establishing an index of slope stability over large areas. The method allows the relative landslide susceptibility to be computed over large areas using a discrete combination of geological/geomorphological parameters. MAP was applied to a region in the Peak District, Derbyshire. The model identified key geological/geomorphological parameters involved in deep-seated failures, provided an effective means of classifying the stability of slopes over a large area and successfully indicated sites of previously unmapped landslides. The resultant regional landslide susceptibility index provides useful preliminary information for use at the pre-site/reconnaissance stages, of large-scale civil engineering works such as highway construction. Unlike deep-seated failures, shallow translational slides usually do not prevent the use of areas above and below the failure, however, they can cause considerable inconvenience and expense When remedial engineering works are necessary. An investigation was undertaken in order to establish the precise critical state of geomorphological factors involved in shallow translational landsliding in the Peak District. Back calculations based on the Infinite Slope Stability Model showed how the factor of safety against shallow translational sliding changed as one geomorphological parameter varied. The value of the factor of safety was very sensitive to changes in the values of effective cohesion and piezometric height, moderately sensitive to changes in the values of regolith depth and the angle of slope inclination and insensitive to changes in the values of angle of friction with respect to effective stresses and soil unit weight. The recognition of such meso/micro geomorphological thresholds is not only important for geomorphologists concerned with landform evolution, it is also fundamental to successful and safe engineering practices