Landslide debris barrier design - frestanding timber wall

[bayfisher]

We have considered a building platform near the base of a moderate to steep slope that has experienced past landslope instability. Soil instability is limited to silt/clay flows due to saturation.
Does anybody know of any literature with respect to determining landslide impact forces for a mobilised soilmass with respect to design of a freestanding timber wall built to take the impact of the slide and protect the structure directly downslope.
Also, does anybody know of any literature that considers how to derive the pressure applied to the wall with respect to its design under dynamic conditions.

 

[PEinc]

If you have a landslide condition, you need to hire a local geotechnical engineer who is experienced in performing slope stability analyses.

 

[bayfisher]

We are the local geotech engineer, and we have run slope stability analyses to determine the volume of the failure mass. I'm interested in determining the design of a freestanding retaining wall as an option to protect the building platform from the debris flow. Normally, we'd design an earthbund upslope of the platform to collect the materials, but on this site they are a little tight for available land area.

 

[PEinc]

Does your slope stability program allow you to add a stabilizing force to the slope so that the FS becomes acceptable?

 

[bayfisher]

Yes, we use SLIDE and US Army Corps methods to determine lateral forces required to prevent a mass from mobilising (or achieve a required FoS for a slope.
What I am trying to determine is design of a wall at the base of a slope to collect debris that has mobilised from the top of the slope. I am tring to determine the force that would be applied to the wall at the moment of impact as it would not just be something as simple as F = M x A.
Normally, for a wall design we adopt Pa = Ka x Gamma x Height^2 x (pole spacing) to determine loads on each pole - with the load applied at H/3. Obviously all of this changes with the nature of the load being applied by a debris flow.

 

[oldestguy]

I think there is a lot more to your problem than impact forces. If you can visualize say a snow avalanche and what it does, it would seem that more importantly you need to design a wall of sufficient height to hold a whole lot more material than just the thickness of the flow. How much volume of soil will finally stop at your wall? and what will its final stabilized shape look like? It won't look so neat if that wall is over-topped by a massive flow volume.

 

[bayfisher]

Thanks oldestguy. We have already determined runout angles based on the soils present at the site and we have indications of flow volumes. At the proposed wall position it wouldn't need to be any more than 2 metres high to collect the slump volume and prevent the soil mass impacting the proposed dwelling.
Slump volume is about 800 cubic metres (20 metres wide x 3 metres deep x 15 metres up slope), mobilised from say 30 to 50 metres upslope. We aren't talking massive volumes, just small scale landslips.

 

[GabionGuy]

I would suggest looking into gabions. There has been a substantial number of free standing rockfall and avalanche structures built around the world. The impact energy these structures can withstand is incredible (10000kJ+)