CBR value 1

[shazi1]

For pavement design we have backfill material with ascending values of CBR, eg. subgrade CBR: 15 %, Aggregate Base 80%.
What will be effects if bottom layer has high CBR with respect to succeeding layer?
Also,I want to know what is significance of permeability of soil ??

 

[Ron]

shazi1....the result of a stiff layer below a less stiff layer is further compaction of the middle layer, with time and traffic. Rather than deflection attenuation as you go down the layers, you get less deflection transfer through the less stiff layer, resulting in more compaction. This results in higher stresses at the bottom of the first layer (thus earlier fatigue cracking).

 

[shazi1]

Thanks Ron, and regarding permeability of soil.. what are desired properties and significance for subgrade, subbase?