Landslides can have devastating impacts. They can move and
destroy roads, rail, cars and even topple buildings. Having a good
understanding behind the causes of slope instability is critical for
engineering and can be a matter of life or death.
Collapse of a
hillside causing roads to break up and risking lives. (By photographer: Liz
Roll, uploaded by User Storm05 on en.wikipedia - This image is from the FEMA
Photo Library., Public Domain, https://commons.wikimedia.org/w/index.php?curid=1121971,
accessed 27/05/2020)
What pulls you towards the ground
when you are at the top of a slide? The answer is gravity. You have probably
noticed that when you wear different clothes you might go down the slide faster
or slower. This is because of friction.
Reducing friction will make you move faster down a slide. Land can move for the same reasons. When land
moves down slope it is known as a landslide.
Rough surfaces cannot
glide past each other as easily as smooth surfaces. (https://upload.wikimedia.org/wikipedia/commons/2/24/Friction_between_surfaces.jpg,
accessed 27/05/2020)
Landslides can be triggered by
earthquakes, volcanoes, heavy rain and even large vibrations from machinery or
building work.
This railway
clings to the mountainside. It is known as the Death Railway. (https://www.wallpaperflare.com/yellow-train-on-rails-by-a-mountainside-cliff-thailand-kanchanaburi-wallpaper-znhsm,
accessed 27/05/2020)
When engineers design roads and railway lines, they must
consider the terrain that they are passing through. Going up steep hills is
avoided and so paths are often cut out of the hillside to make routes that are easier
and safer for transport. It is vital
that engineers have a good understanding of the material which is being removed
from the hillside to ensure maximum slope stability and avoid landslides from
happening.
There are a few factors that can affect the maximum slope a
material can be stabilised at. How compact the material is will greatly alter
slope stability. A well compacted material, like rock, will generally be stable
and can be cut nearly vertical. However,
if a sediment is very loosely packed it will be unstable. The shape and size of
sediments can also greatly affect slope stability. Rough, uneven sediments will
have more frictional force between them, this holds them together more. Smaller particles are also likely to fit
together more tightly, as the smaller pore spaces allow in less fluid which can
act as a lubricant.
Investigate these concepts for yourself, try the angle of
repose activity in the Landslides STEM project, which has a corresponding video.
This retaining
wall was built to prevent a landslide over this former railway line. (https://www.geograph.org.uk/photo/5863731,
accessed 27/05/2020)
Engineers will conduct investigations to calculate the
safest angle to cut into a hillside. Reinforcements and structures may also be
added to the slope to improve safety, such as rock bolts and retaining walls.
- For more information on slope stability read this article: Factors That Control Slope Stability