Change of stabilised base course(C2)to crushed stone base(CRR)

[defg]

I'm currently supervison a road which formally was designed to be constructed with stabilised base course(C2).But due to unavailable suitable gravel materials to ssiut for this base course works prior to stabilisation,the Contractor requested to change the base course from stabilised layer to crushed stone base as the area is full of granite stones.The formally designed stabilised base thickness was 150mm thick.But the Client insisted the Contractor to use 200mmthick of crushed stones and to be compacted in two latyers,i.e 100mm thick then followed by another 100mm thick.Ifailed to understand this,which is more stronger stabilised base course(C2) of 150mm thick or crushed stone of similar thickness.Idon't understand why the contractor to use more thickness for crushed stone(200mm thick)instead of 150mmthick as per design!!!!

 

[Ron]

While stone might be or seem "stronger" as a particle, depending on its gradation, it might not be as stable as the stabilized base material. If the crushed stone does not have a uniform gradation to include some fines, then stability will suffer.

The reason for the two layers of compaction is to make sure that bridging doesn't occur and the lower section doesn't get compacted properly.