Road base construction 2

[N3M4N]

All,

while constructing a road are there any concern with construction of the roadbed from a geotechnical or pavement engineering perspective if the road was constructed as per below:

Asphalt 100mm (Density 2500 kg/m3)
Gran A 150 mm (Density 2200 kg/m3)
Gran B 200 mm (Density 1800 kg/m3)
Gran A 100 mm (Density 2200 kg/m3)
subgrade-sand (almost like beach sand)(Density 1700 kg/m3)

The question is whether sandwiching Gran B in between two layers of Gran A is problematic/concern or not?

 

[oldestguy]

It's a little uncommon here (USA)to use so many different layers, but the densities look good. A lot spends on sickness of layers and of course the traffic. Shear strength of the lighter material may be weaker than others and usually that's for the bottom layer.

 

[Ron]

Agree with OG....also, even though there is not a lot of difference between the gradation requirements of A and B, Granular B can have some coarser material. I don't like to see a finer material above a potentially coarser material in pavement construction. Unless there is a geotextile separator, there is a potential for finer material to migrate into the coarser material, thus causing a volume reduction (settlement).

 

[ACtrafficengr]

Is the lower layer of A meant as a filter layer to keep the subgrade sand from infiltrating your subbase? Would separation fabric be cheaper?

My glass has a v/c ratio of 0.5

Maybe the tyranny of Murphy is the penalty for hubris. -

http://xkcd.com/319/

 

[cvg]

without having the gradations of A and B and assuming as with most road base that the gran A and B are "well graded" mixtures, than I dont see migration being a high risk. but more information might prevent all the speculation...

 

[BigH]

OP is probably referring to Ontario's OPSS 1010 (I believe) . . . Not sure why you want to sandwich the Gran B UNLESS the lower Gran A is already in place. Normal pracice when I was in ON was to use Gran B as lowest, then Gran A and then the asphalt. Gran A is NOT free draining like everyone thinks.