How can landslides be surveyed？
The purpose of surveying landslides is to provide the most effective and economical data related to landslide prevention and mitigation planning. In other words, the landslide survey results enable us to know the “location of landslide, engineering to be adopted and estimated results”. Landslide surveys can be divided into “status survey” and “mechanism survey” according to their prioritization. The former one is to survey all types of landslide-induced ground surface phenomena or signs in landslide sites inferred based on their geological and topographical conditions; the latter one, on the other hand, requires the planning of emergency countermeasures. Therefore, the scope of general status surveys includes the sliding range, sliding direction and slippage, whereas the geological survey at the stage of field survey (on-site survey) is to survey the landslide topographic features and geological properties (ex. lithology, stratum, structure) according to the interpretation results of topographic map, geological map and aerial photos. The purposes thereof are to understand the landslide range, type and sliding direction; and to zone the landslides.
The mechanism survey, on the other hand, is to conduct a three-dimensional spatial survey on sliding blocks’ geological conditions, depth, sliding pattern, scale and hydrology. Although the landslide failure mechanism is rather complicated, it helps us to understand the dynamics of landslide triggering factor, grounder water; subsurface geology; state of weathering and metamorphism; depth of sliding block; and slope stability analysis required soil mechanics parameters. Therefore, with respect to determining the types and methods of prevention and mitigation engineering works, mechanism survey is an extremely important work. Besides, the survey accuracy can decide if the landslide prevention and mitigation engineering is succeeded or not. In general, mechanism survey items include geophysical exploration, core drilling, sliding surface survey, groundwater survey, soil characteristics survey and so on.
As landslide features can change according to the type thereof, the survey methods shall be selected and applied according to the landslide type to maximize their effectiveness.