Water canal landslide 2

[SA07]

Hi
A water canal supplying water for irrigation and a power plant is damaged by a landslide as attached picture.
There is a valley. At the bottom there is a river. There is a small dam across the river. The dam supplies the canal. At various parts, the canal is dug into the slope of the soil. At some parts, there is concrete canal.
Can you tell us what can be done to prevent such landslide? It is in Mauritius, a tropical country in Indian Ocean. There were mainly bamboo trees on the landslide. Thanks

 

[STrctPono]

I have a project very similar to this that is ongoing and is also in an isolated tropical location. Looks like the source of your landslide is not just loose debris being carried down the hill in heavy rain... you had a slope stability failure. You would need to either cut back that slope to a stable condition or mechanically stabilize it with tie-back anchors and shotcrete. I sure hope you have a geotechnical engineer on board for this project.

 

[geotechguy1]

Stability of steep tropical hill slopes is often governed by transient porewater / matric suction effects and vegetation.

There are many options:

Preventative:

[ul]
[li]Plant vegetation with deep roots (eg. Vetever grass or trees that have deep root systems[/li]
[li]Plant trees from the mid slope towards the toe but consider removing heavy trees at the crest. Trees with the right type of root system will essentially turn into a shallow pile retaining wall[/li]
[li]Implement engineering measures to reduce infiltration (and thus the destruction of matric suctions). In Hong Kong a material called chunam is used for this purpose but alternatively shotcrete or something similar. You can also achieve a similar effect with compacted low permeability material in the upper couple of meters or with a capillary. Doing this removes the option to have vegetation in place though [/li]
[li]Stabilisation of the toe - it sounds like the toe of the slope has been cut out which is bad news for slope stability - some form of stabilisation should be considered at the toe of the slope[/li]
[/ul]

Remediation options once the failure has already occurred include various types of pile retaining walls, shotcrete and anchors, etc.

Note that most of the preventative measures probably only work for shallow landslides. If you get a freak 1/10000 year rainstorm which causes the phreatic surface to rise all the way to grade all bets are off

 

[GeoEnvGuy]

It is upto the governments to address the issue of landslides, especially in undeveloped areas. This of course means identify areas of concern and prioritize with limited budgets and limited motivation to address potential issues.

 

[SA07]

This is a critical supply of water for our plant. We are in a drought period now. The flow from other sources of supply has decreased much. We cannot rely on the government. Also the canal is for our company.

 

[Lomarandil]

Stars for StrctPono and Geotechguy...

The optimum solution chosen will also depend on the length of canal affected. If it's only a short segment, it probably makes sense to just put the labor in and cut back the slope, then plant grasses and shrubs to stabilize. If this is a long segment with lots of landslide zones, you might consider a more technical solution like walls or shotcrete (in which case a geotechnical evaluation would be really necessary).

----
just call me Lo.

 

[SA07]

Thanks for the advice.
For the time being, we have install metal pipes suspended by chain fixed by concrete blocks higher up where the ground is horizontal over 40 m. We have put the water canal into service.