Classification of soils for use in Highway Construction 5

[doolittle2]

Hi
Can any of the rock hounds out there help me with this one, can an argillaceous rock be classified as Class 1 granular material for use in UK highway construction.
In it's as dug state this material is soft/medium rock known locally as shillet sic. but when crushed and exposed to rain becomes quite plastic and ruts under traffic.
When rubbed between the fingers leaves a talc like sheen on the skin.
Also when crushed does not se3em to contain any sands, gravels or other types of rock.
Thanks for reading this

Doolittle2

 

[soiledup]

It sounds to me like you are working in Cornwall. Shillet?! Thats a local term I'd recoginse anywhere!

I think you need some laboratory testing to classify the material accordingly. If you are in Cornwall, you could try a locally based geotechnial firm to see if thier labs will do materials testing like,,,,,mine!

 

[doolittle2]

Hi Soiledup

You sound one clued up s**tkicker, you're spot on, I am working in Cornwall (just) but my problem is with geo-tech opinion at the moment or, to be fair, my problem is with my head, which I cannot get to accept that whatever the in-situ or as dug state of a material is, if it turns to Kak after a bit of rain and construction traffic and feels as slippery as a you know what after a good session how can it be classed as granular which, as you know the Class 1s are.
Is it me, the spec or the classifiers who have it wrong.

doolittle2

 

[BigH]

Might this not be a good material to determine the durability via the Micro-Deval test? Rather than the LA Abrasion test, the Micro-Deval puts a sample of aggregate in a jar of small steel balls and water in order to determine the durability. You can google Micro-Deval Abrasion - British Columbia's Ministry of Transportation has a circular for its use - something like 25% degradation maximum for road base.

 

[jdonville]

doolittle2,

Sounds to me like it's best classified as an expansive shale. Tricky.

Jeff

 

[iandig]

Its not just limited to a Cornish sourced material, as you get exactly the same with many of the limestones quarried in Oxfordshire. Key criteria for this material is the moisture content range in which it needs to be placed at, plus the level of compaction. Unfortunately, once it gets wet, it rapidly degrades. The adoption of the 'Los Angeles Abrasion' test for many of the granular materials was done for this very reason when it replaced the previous 'durability/strength' test of 10% Fines Value. The LAA test is supposed to replicate the action of the compaction plant when the material is compacted, so my reccomendation would be to add in an extra requirement for the Class 1 granular material of this test [typically it would only be used for Class 6 Granular materials] with a nominal value of better than 50. This would require an amendment to the contract specification, but should eliminate the use of materials which are likley to degrade during placement and compaction. Not sure at this stage of the project of it will be of any help to you, but I hope so.

 

[soiledup]

Yeah, I appreciate this is tricky, but you need only look at local projects to determine its suitability. The Highways Agency (see A30 and A38) seem to have very little problems with it and I know that if this stuff is compacted properly in thin layers it can be very useful to re-use. It is like anything else on construction and should be subject to an insitu material testing program (CBR's, plates, Sand replacements for density with nuclear density gauge). Lab testing can only do so much, experience and good insitu testing can do the rest.

Good Luck - incidentially, 'only just in Cornwall'?? now I'm curious. Where are you working?

 

[SiteMonkey]

Hi doolittle2

As mentioned by soiledup you will need some PSDs to properly classify the material to the highway spec. Experience would suggest that the weathered shillet material usually falls into a Classes 2A-2D 'cohesive material'. I'd suggest PSDs and MCs/Atterbergs on the material to fully classify it for a method specification.

 

[doolittle2]

Hi Soiled Up and SiteMonkey

Thanks for the info re Highways Agency contracts and their use of this material I'll have to take a look see at those locations especially as one of them is only just in Cornwall.
Soiledup your advice on in-situ testing is valable as is yours
SiteMonkey on the need to accurately classify the material prior to use within the works my only query is, with variable material presumably the testing regime for classification should be an ongoing programme?

regards

Doolittle2