Geotechnical thresholds in the Lanzhou loess of China

Failure of cementation bonds leading to soil structure collapse and slope failure is a major problem encountered in loess slopes in the Lanzhou region of China. Typical physical properties (low plasticity indices, short-range bonds. decrease in shear strength upon saturation) show little variation throughout the loess strata. However, important variations in the modes of failure and collapse potential exist which are related to varying thresholds of cementation bond failure and packing transformations. When geotechnical thresholds are exceeded, metastable loess can rapidly transform from an open to close particle packing; a phenomenon enhanced by leaching processes and degradation of cementation bonds. Geotechnical parameters from laboratory and in situ tests provide an insight into the variation of cementation bond 'condition' which, in turn, provides enhanced understanding of processes underlying slope instability development and the triggering of catastrophic mass movements in loess. (C) 2001 Published by Elsevier Science Ltd.