Classification and stability assessment for chalk cuttings: the Metropolitan Line case study

This paper describes the findings of an assessment related to the nature an d impact of slope instability for 20 km of chalk cuttings on the Metropolit an Line, and which forms an integral element of London Underground Ltd's Ea rth Structures Management Strategy. A desk study and detailed geomorphologi cal field mapping were utilized in order to develop a comprehensive classif ication scheme for the chalk cuttings. The classification depends primarily on cut-slope geometry and proportion of superficial deposits found in the slope. Restrictive thresholds were identified between classes that controll ed the type of instability hazards present. The relative risk to the track was assessed which enabled targeting of future remedial measures to the mos t appropriate locations and the development of a cost-effective maintenance strategy.