Allowed Base course and subbase course material for island road

[Promdi86]

Hi guys!

I am currently working on a project in an island in the Pacific where it is proposed that the Base course and Subbase course would consist 2inch to 4inch crushed stones mixed with coral sand and followed by PCCP (basically it means base and subbase course will be one and the same). Has this been done before? If yes, what tests have been done and standards used for this? If not, can anyone give me tips on how to do this? Thank you so much

 

[Ron]

What type of traffic? You don't give a thickness of the PCCP, but it would appear that your pavement section is for highly loaded pavement.

Usually, unless you have extraordinary loading or if you have poor subgrade soils, you don't need a subbase course for PCCP (I noticed that you use the term "base"....that's usually not used with PCCP.)

If you have reasonably stable sands and can confine the pavement edges, then for most traffic loadings the PCCP can be placed directly on the compacted sand subgrade. If unstable, do as proposed, making sure that the subbase is free draining.

 

[Promdi86]

Thank you for replying Ron. The subgrade soil is very poor, with groundwater table about 2-4feet from the natural grade line. We still don't know the ratio of grsvel to sand would be appropriate. Is there a way to use ASTM standards on this one?

 

[Ron]

Promdi86...you can use any standards allowable in your area. Nothing wrong with using ASTM standards for this, as long as those are generally applicable for your area by code or accepted practice.

Please give a bit more information on your subgrade soils...what type are they (sand, silt,clay,gravel, etc.), what character (calcareous, quartzite, basalt, etc.), organic?

Have you run a CBR or other stability tests on the subgrade soils? If so, what values are you getting?

Try to keep the groundwater level to about 18" below the bottom of whatever base material you decide to use if a flexible pavement. It can be a bit higher in a rigid pavement, but you have to be careful about pumping and loss of slab support.