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# shear strength of subbase under gravel road2

## shear strength of subbase under gravel road

(OP)
what is the best way to calculate the stress' on a subbase under a 3 layer gravel road bed, i.e., 6" of 3/4"-0, over 9" of 1-1/2" -0, over compacted subbgrade (60,000 lb load).  Is the 3 layer theory as stated in Yoder/ Witczak (principles of pavement design, 2nd edition) valid for this particular case?  Also, when I calculate the stress in the subbase, where would I find typical values of shear strength in various soil types for comparison? Can anyone tell me where I can find typical values for the modulus of elasticity for compacted granular backfill and or various compacted soil types?

### RE: shear strength of subbase under gravel road

2
The elastic layer process given in Yoder and Witczak is valid for your problem.  There's even "public domain" program that will easily compute these stresses for you (ELSYM 5).

I'm not sure why you want to check the shear stress in the subgrade under a pavement.  I assume you have your reasons, but it is not one of the controlling factors in a pavement analysis.  You need to look at vertical deformation at the top of the subgrade, as this parameter controls rutting, not the shear strength of the soil (though all are interrelated).  There are several correlation values for vertical deformation at the top of the subgrade.  Commonly used state Departments of Transportation values are Kentucky, California, etc.  Both Shell and Chevron have correlation values as well.

### RE: shear strength of subbase under gravel road

(OP)
Thanks for the info ... where might I find "ELSYM 5" on the net ...

### RE: shear strength of subbase under gravel road

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