Landslides
Landslides are an extremely dangerous and
often overlooked side of geology. It is estimated that
around 25-50 people in the U.S. die from landslides every
year. They are very difficult to prevent and to analyze.
Landslide Factor of Safety
To describe the slope stability of a slope we use the
factor of safety, this is the ratio of the resisting
forces to the driving forces. When resisting forces are
greater than driving forces the result will be greater
than one, indicating that the slope will not fail. When
driving forces are greater the result is less than one,
meaning the slope will fail. The equation can be seen in
the figure below.
The strength of the rock or soil comes from
internal friction and cohesive strength. Cohesive strength
is measured in force per unit area. Rocks have a much
higher cohesive value than that of soil or silt. Internal
friction is represented by the internal angle of friction.
It is caused by grain size and properties, this ranges
from 0 to 45.