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Hi, I am involved in a landfill closure project and just wondering what type of major geotechnical information/analysis may be required for this project.
The landfill is 5 m height with 1:2 slopes. So far, I am considering the following:
1. I expect that some kind of slope stability analysis will be required.
2. Also, I think that groundwater level information is important as well.
3. Check properties of soils underneath the landfill to address stability and settlement issues.

Any other items that I may need to consider?

RE: Landfill

Final cover material properties are critical as to how it "performs". For example, in Wisconsin some 20 years ago or so the Department engineer leaders handing them were going to show me how a closure they supervised that was doing so well, since I was consultant for a different landfill closure. It was to be an example to follow. The site was in an area where high plasticity clays were abundant. There was about 4 feet of this cover and the job was a few years old. A thick growth of weeds were covering the high plasticity clay area and as we walked over the site I noticed cracks. I had a folding ruler along and as the engineers who had bragged about their job watched, that ruler went all the down in the cracks to the garbage and trash. Needless to say there was not much bragging conversation in the car as we went home.
That so called covering job was totally worthless. The moral to this story is that the cover must be capable of going through wet and dry seasons without cracking and allowing infiltration of rain water, etc. You may have to put up with a little leakage of the cover, but certainly you don't want it full of deep cracks.

RE: Landfill

leachate collection system
landfill gas collection system
oh, and drainage

RE: Landfill

OG and cvg, thanks for your responses.

OG, how can we avoid cracking of covering materials? I think that you have to keep the moisture there (not let the cover to dry) otherwise cracks will appear. But not sure how can you keep the moisture...

cvg, yes, the designers are taking considerations about drainage, but not sure how much geotechnical input is needed for drainage design, as I think that drainage will be composed of man-made surface structures to divert the flow and no let it go thru the landfill soils...

RE: Landfill

Some things come to mind -- membrane roofing and ballistic vests/radial tires

This cover is not unlike the roofing material, in that it must survive weather and sun without leaking, and there really isn't much that works 100% forever. Ballistic vests and radial tires are typically multilayered constructs. So, maybe sort of layered structure with membrane roofing as one of the layers and some sort of aramid to minimize punctures?

TTFN (ta ta for now)
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RE: Landfill

Not only the design of the landfill cover is important, your Construction Quality Assurance/Control (CQA/CQC) Plan is very important. In this plan, you'll need to indicate how the cap will be constructed, the materials used, the testing methods for the different materials used, the frequency of the testing and the passing criteria.

For example, for a clay liner system, you'll have testing for the borrow source (i.e., the source of the clay) for x samples per day and per volume of material. At the site, you'll be limited to the size of the lifts (e.g., 9 inches placed with a maximum compaction size of 4 inches), the hydraulic conductivity (or permeability), dry density, etc. You'll have so many samples per lift.

RE: Landfill

The problem of high shrinkage is related to the property of a some clay minerals that have great volume change with moisture changes, such as montmorillonite and some other clays. If you can avoid these types of clay minerals, that is the best way. However, otherwise minimizing that mineral (clay content)and developing or finding a very well graded material, you can then go to compaction at a minimum density to get approval from a regulating agency, hopefully. Once they understand the clay mineral factor, maybe some relief of specs on clay content percentage may occur. Laboratory permeability tests are needed to prove these specs as suitable. Don't also forget the fact plant growth can take up a lot of the moisture, in addition to dry weather effects. If you need help on identifying clay minerals, soil scientists in university agricultural departments may help.

RE: Landfill

the drainage structures on a landfill are generally constructed in the cover layer. They will consist of earthen channels, riprap and other erosion protection. maybe some pipe down drains, but maybe not.

Not sure what you mean by man made materials.

most of the landfill / cover failures I have seen were related to the following:

clay cover increases the runoff to almost 100%
landfill settles to the point that drainage channels no longer have adequate slope. they have low spots (belly's) that collect water and do not drain. these spots get saturated, the water does not drain adequately and goes over the side and then runs down the face of the landfill. this causes erosion which pipes and headcuts to the top of the landfill, exposing waste. landfill cover material is brought in and packed in the erosion gulley. the next big rain it happens again.

So I don't know if this is related to geotechnical input or if this is strictly the civil engineer's problem, but settlement of the cover material and impact on drainage is a huge issue.

RE: Landfill

Thanks all for your input. Understood that drainage, cover material and QC are very important factors for landfill closure design. Also, do you know any good regulations or specs from any state that can I use as a reference? Thanks again!!

RE: Landfill

The State of Indiana rules are here. Specifically, 329 IAC 10-17-5 deals with the Soil component of the liner; construction and quality assurance/quality control requirements. Note: the rules dealing with constructing the subgrade of a landfill are the same as the final cover. You probably should check where you're putting the cap as they may have specific requirements for the CQA/CQC.

One thing I thought was odd was the slope of your cap of 1:2. Typically, the side slopes are 3 horizontal to 1 vertical. I've seen some a little steeper, but never 1 horizontal to 2 vertical. If that is your actual slope, you may have problems establishing vegetation on the cap as well as performing maintenance.

RE: Landfill

Thanks for the reference zelgar. I will take a look at the section you are referring to. You are right, for mowing maintenance I have normally seen 1:3 slopes. However, the available information that I got shows 1:2 slopes. I have not been at the job site yet, so just trying to check the site with Google Earth but it was too helpful. Again thanks for the info.

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