Landslides – Mitigation
Posted by Kshitija Nadgouda on June 17, 2006
Mitigation of a landslide means reducing the effects or the intensity of the landslide. Most methods of mitigation overlap with preventive measures so the subject matter in this post will overlap with the post on Landslides-Prevention. However, in my opinion, the importance of landslide mitigation calls for a separate post.
After a landslide occurs, the first task is to remove the mass of soil that has been displaced from its original position so that human life, if disrupted, can get back to normal. The next task is to determine the exact cause of the landslide in order to decide on the mitigation plan.
First rule of thumb for landslide mitigation is to stabilize the slope.
The slope can be stabilized by one or a combination of any or all of the following methods:
- Remove the landslide soil material and replace it will engineered fill
- Shear keys with drainage
- Removal of top
- Retaining Walls
- Steel nets
- Soil Nails
I discussed all these points in the previous post (Landslides-Prevention), but let us discuss them in detail here.
Remove and replace
This is a common technique specially used if the landslide area is small and if construction is ongoing in the area of the landslide.
Shear keys with drainage
Shear keys are typically used in conjunction with the “remove and replace” mitigation technique. Shear key also known as a keyway is a trench excavated into the competent soil material so that the new fill placed over the natural slope firmly keys into the existing soil. Placing a drainage pipe within a keyway futher improves the stability of the slope by reducing the effect of groundwater fluctuations.
In simple words, a buttress is a man-made mound or hill of soil (fill slope or berm) placed at the toe of the slope. The buttress increases the resisting forces and thus prevents material from moving towards the toe of the slope. In some cases, it may also be a metal or concrete beam providing additional support to a retaining wall constructed at the toe of a slope.
(Courtsey Kansas Geological Survey)
Removal of top
An extenstion of the same principle as the fill buttress, another method is to remove the soil from the top of slope, thereby reducing the forces driving the slide. This may reduce the total height of the slope and thus help in reducing the driving forces.
Constructing a retaining wall at the toe of the slope acts principally similar to constructing a buttress. The retaining wall may be one of various kinds: gravity wall, gabion wall, modular block walls, reinforced conctrete walls, etc.
Click to see a a larger image
(Courtsey City of Anaheim)
Steel nets or wire meshes
These are usually put up on slopes where danger exists of the continually sliding mass to obstruct everyday life. The most commong example is putting wire meshes on sliding slopes that exist along roads.
Soil Nails are typically steel bars inserted into the soil at close intervals to reinforce the existing slope. THe face is then typically sprayed with shotcrete.
Click to see a larger image
(Courtsey USACoE, Memphis District)
Copyright Kshitija Nadgouda.