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Landslides in the thick loess of Northwest China: mechanisms and mitigation

An analysis has been carried out into the location, size and type of the landslides of the Greater Lanzhou region, Gansu Province, China, where there is thick loess. This exercise involved classic geological and geomorphological mapping, topographical survey including terrestrial photogrammetry, and creation of a Geographical Information System (GIS) using remote sensed imagery from the SPOT and LANDSAT/TM platforms. Particle size over 300 samples of Lanzhou loess was analyzed, a calcimeter was used to determined percentages of calcite and dolomite, and X-ray diffractometry (XRD) was employed to determine the clay mineralogy of the loess. Soil mechanical properties were determined using British Standard geomechanical tests (BS 1377), and the hydraulic conductivity of loess at several sites was determined using standard infiltrometers.

The distribution of landslides in loess terrain is not uniform and reflects important influences by rainfall type and distribution, subjacent bedrock slope and lithology, loess thickness, seismic shock, and human activity. Thus, the distribution is strongly clustered. The loess hydrological system is distinctive, the macrostructure (loess karst) being much more influential in destabilising slopes than the intact (micro) structure.

Loess is intermediate in many characteristics and, as such, is not catered for in established classifications of landslides (which are dominated by considerations of clayey or sandy materials). This being the case, the current models best explaining landsliding in loess emphasise bypass drainage, basal saturation, flowslide and spread type motion and failure under tension of the essentially dry slide mass. Human activity, especially in urban areas and along rail and road routes, materially increases the landslide hazard.

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Egham hill
United Kingdom
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