Capping Layer

[usas]

Hi, this is my first time wriing to the forum. Hope you can accomodate me. Can anyone help me regarding capping layer grading curve? I've been searching for the spec of this material which is usually used on railway embankment below the ballast layer. I'm considering whether this material would make an option as flexible surface for storage storage yard.
Rgrds & TQ.

 

[Dirtmaster]

this is a little out of my field but, As I understand capping layers, they (and there are several different types)
are not designed to be a "wearing course". They are intended
to strengthen the sub-grade before base material is placed.

i think that a layer of graded aggregate base (gab) would
make a better parking lot than a capping layer would.

Slope, traffic loading, turn radii, sub-grade stability all play a part in how much the surface will be rutted and erroded.

If your site is fairly firm (a CBR of 15% or so it may not need an underlayment or capping layer.

stripping of any organic topsoil should be performed and the sub strata tested for firmness (strength & Compaction).

If this parking lot represents a large investment, you should consult a geotechnical engineer.

 

[usas]

Thanks Dirtmaster,
Maybe be I should have explained more clearly. The site is on a well compacted fill and traffic is not a problem as paved road will be provided. The storage yard is about 40% of the project area. Of course top soil will be removed prior to anything and the ground will be levelled and compacted. The storage yard is to store fire wood, oil palm and cocunut husk.

I am considering whether capping material can provide an almost impermeable layer while at the same time economical solution when compared to gravel. I am looking for the grading curve for this capping material and would appreciate if anyone can give me or tell me where I can find them.

 

[BigH]

Usas - are you really looking for a grading curve - you've indicated that you want this to be almost impermeable. This implies you want a fine grained soil - and grading curves for fine grain soils are only approximations. Normally for capping layers of fine grained soils, etc., you would be implying Atterberg Limits - such as PI<15 or PI<12. You can check out TRRL's Overseas Research Note (ORN 3) - they have a good summary of various materials that would be used "in the tropics" but would still be applicable. Sorry, I don't have the URL - I've got the document.