THE LOESS OF NORTH-CENTRAL CHINA - GEOTECHNICAL PROPERTIES AND THEIR RELATION TO SLOPE STABILITY

Loess is an aeolian deposit consisting of predominantly silt-sized qua rtz particles, and containing variable amounts of clay-sized minerals. Loess is generally classified as a water-softening material, because upon wetting the loess fabric rapidly weakens or collapses. The strain hardening of Malan loess and the brittle failure of Lishi and Wucheng loess are in strong contrast to the failure behaviour of these loess deposits in a remoulded state. From tests carried out on samples with varying moisture contents, using a modified Bromhead ring shear appara tus, it was found that the effective apparent cohesion gradually incre ases and the effective internal friction angle decreases with an incre ase in moisture content. When the moisture content reaches a material- specific threshold, the effective cohesion decreases rapidly and the e ffective internal friction angle stabilises at a residual value. The f requent failure of loess slopes in the western part of the Chinese Loe ss Plateau is closely related to progressive weathering along zones in these slopes, which causes a dramatic decrease in strength from the p eak strength condition. Progressive weathering is common in the loess slopes in the western part of the Chinese Loess Plateau. During the pr ocess shear strength reduction along potential slip surfaces may be ac hieved by leaching of readily soluble salts, destruction of cementatio n bonds, and redistribution of particles. Localized collapse of the lo ess fabric causes internal deformation and consequently peak strength conditions are concentrated on a progressively smaller area of the fai lure plane. Therefore, the mode of failure of loess slopes is generall y determined by brittle failure of the undisturbed, and unweathered, c entral parts of the slopes. It is important that both the weathered an d unweathered strength of the loess materials in this area be establis hed in order to analyze the stability of existing loess slopes, many o f which are steep and lie directly above domestic and industrial urban areas.