Stabilization of sand dune in seismic zones 2

[Atros]

Hello,

I want to hear your thought of doing a cut in a sand dune of 100 m height with natural slope of 2H:1V. We need to cut for a road about 8 m, and then use a 2V:1H slope. The soil is a SP-SM sand dune, very loose. What kind of stabilization system (ie. soil nailings) would you recommend?

Thanks friends!

 

[Mad Mike]

Soil nailing in very loose dune sands can be problematic...the sands don't stand unsupported in benches for the duration of construction and self-drilling soil nails are needed because conventional drill holes collapse.

Your proposed cut is a serious endeavour so I'd guess the best way forward would be a piled approach. I'd just add that with slopes of 1:2 (V:H), your sand dune is in a marginal state of stability. Heavy vibrations during construction will probably bring it down straight over the top of your cutting which would trigger the snowball effect...

All the best,
Mike

 

[Mad Mike]

Sorry, another consideration regarding dune slopes- when they exist in a marginally stable state, as yours does, there is a defined "zone of soil creep" which, for a 1:2 natural slope, would be effective in the upper ~6m of soil profile, measured perpendicular to slope. This sand mantle is subject to continual, on-going downslope movement.

Any shallowly-founded retaining structures supporting your cut would be globally unstable for the above reasons.

Cheers,
Mike

 

[dik]

1:2 or 1:3... I don't think the sand would be stable without a more shallow slope, and, even then would require a lot of maintenance.

Dik

 

[Atros]

Hi, thanks for your replies. Seismic refraction results: 30 m of sand with Vp < 450 m/s.

What kind of pile approach would you suggest?

 

[BigHarvey]

Have a look at Texsol

This material is a mixture of continuous thread and sand. It has an apparent cohesion of 0.1 MPa and a very high friction angle and can be used as a retaining structure almost vertical.

http://www.eiffageinfrastructures.com/texsol

 

[fattdad]

if it's an active dune, the existing safety factor is unity. Preliminary engineering should return a safety factor of 1.3 to 1.5. If federal money is involved, you then need to ask if the safety factor is only for the wall or is it for the wall/slope "system?" Nice thing about a dune is it's not saturated, so there's no liquefaction to worry about!

Folks use shear walls to stabilize against shaking. May work?

f-d

ípapß gordo ainÆt no madre flaca!

 

[Sjotroll]

You might do jet grouting or compaction grouting on a certain raster and at a certain angle like you would with nails or anchors to stabilize the slope. By grouting you can achieve higher strength, higher stiffness while also intersecting the slope and stabilizing it, while also stabilizing your cut. With compaction grouting you would also compact your loose sands to become very dense. For that you would have to specify the most appropriate type of suspension and many other parameters regarding the suspension and grouting procedure.