Low-strength soil grading 2

[DentonM]

Greetings,

What type of equipment is available for grading and earth moving of low strength soils?

I'm working on a site that has bauxite residue, which is over 50 yrs old. When the residue is originally placed, it is pumped and has the consistency of pudding. Typically, the residue has a dry crusty layer that can be scraped off and the low-strength residue is underneath. I think grading or excavating is done incrementally by taking off the crusty layer, waiting for it to dry, and then removing the second crusty layer.

Does anyone know of a better way?

Thanks, in advance, for your assistance.

Denton

 

[GeoPaveTraffic]

A drag line may be a better solution. With a drag line you should be able to remove all of the material at the same time. However, the mobilization costs of a drag line will be greater.

 

[SirAl]

How deep is the material?

 

[cvg]

The following thread in the Earthwork / Grading Engineering Forum addresses drying out and treating material to increase strength.

thread158-94844

 

[DentonM]

Thanks for the valuable post.

One of the things we are considering is the use of gypsum to stabilize (both pH and strength). The gypsum is available on site.

Does anyone know how the effectiveness of gypsum addition compares to lime in terms of stabilizing (not neutralizing)? Also, in my case, the pH is already around 10 or so and lime would not help reduce the pH.

Since my original post, I've found a company (Wilco) that has a specialized piece of equipment that can excavate slurries. The costs is about 3 times that of a convential method, though.

GeoPaveTraffic - Regarding the drag line, I will consider the applicability. I think that it may not work in this situation, b/c the residue may be too competent. I'm looking to grade about 220 acres, so the mob cost will most likely not be too high.

SirAl - I'm looking to cut up to 10 feet in some areas.

 

[cvg]

since the material was originally placed by pumping as a slurry, can you use the same method to remove it from the site?

 

[DentonM]

Pumping might be an option. I will check it out. Thanks.

 

[BigH]

In what fashion do you wish to move the material - that is, is it for site roads? for site buildings? - or are you wanting to remove all of it? If for site roads, you might, be able to use displacement techniques after you remove the crust - of course, this depends on the consistency of the slimes. I once displaced nearly 40 ft of bauxite tailings slimes. If for large areas in plan (as wide as long), then this wouldn't work.

 

[DentonM]

I'm not planning to remove any of the material. I'm planning to move the residue within the 220 acre site to improve drainage. I will most likely mix the residue with gypsum, but I plan to consider the utility of pumping the residue in some areas.