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How can we predict landslide susceptibility?

Each year, there are countless landslide hazards occurred around the world. The primary cause therefor is that the developer ignored the importance of carrying out landslide and landslide susceptibility surveys on the site or its surrounding areas during the planning or development stage. There are a number of factors that are often used to predict regional landslide susceptibility:

1. Slope gradient and earthquake activity

The steeper a natural slope is, the higher susceptibility for its materials to move downslope. As human construction and engineering often make a natural slope steeper, it is likely create sliding blocks if the slope is note appropriately protected. Therefore, before launching construction works, it is a must to carefully survey the slope materials because this type of slopes can easily collapse particularly when it is located in areas with frequent earthquake activities.

 

2. Geology and geological structure

Sites that have soluble rocks at toe or whose rocks can easily be softened by water have relatively higher landslide susceptibility. Such potential can be affected by the strata or joint of dip direction and be further expanded.

3. Accumulation of surface water

Water retained by slope materials can make the slope unstable. The problem is that we are unlikely to drill a hole only to confirm the site’s groundwater level. Therefore, spring water on the slope, continuous wet belt and puddles are valuable signatures, particularly when they are parallel with the slope edge. All of these are signs indicating a high-water content of the slope.

4. Topography and vegetation

A low land encircled by a semi-circle cliff can represent an old landslide. This can be ascertained if (1) the soil and rock materials of the low land form rugged hillocks due to fluid or sliding rock; (2) the vegetation of low land area is smaller or less comparing with surrounding areas. The said phenomenon indicate that there was a landslide at the site in the past and warns the constructors to carefully survey the geology of this site before launching the construction works.

5. Phenomena that can accelerate the creep or collapse of materials

The natural creep is extremely slow. However, if the materials are at the edge of collapse, the speed of creeping can largely increase. Such accelerated creeping process was observed in Italy’s Viont Reservoir before its collapse. Not only can the creeping speed be measured by instruments installed on the slope, but also the creeps can be examined from the ground surface phenomenon. For example, if the recently grown plants or newly established fences or utility poles tilt downslopes, or if there is any deformation or cracks on the road surface, it indicates a high-speed creeping process.

For more information, please go to the “Taiwan Geoscience Portal” website.