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Replacing hard subgrade with another material like engineered backfill material

Replacing hard subgrade with another material like engineered backfill material

Replacing hard subgrade with another material like engineered backfill material

(OP)
I am working for the asphalt contractor and we have this argument with the owners representative about sub grade layer (layer A). The owners representative insist we must follow the design and disregard the actual site condition.

Below is the Asphalt Cross section as per design. The actual site condition, layer A and B is limestone.

Asphalt Road Cross Section Design:
F. 50mm thick - Bituminous Wear Course
E. RC2
D. 100mm thick - Bituminous Base Course
C. MC1
B. 200mm thick - Aggregate Base Course
A. 300mm thick - Sub Grade, CBR>80, MDD>95%

We agree on him to remove the limestone layers on Layer B to accommodate the 200mm Aggregate Base Course, however, we argue that the limestone at Layer A is sufficient enough as base for aggregate base course. The owners rep insist to remove and replace limestone with granular base course.

We find it unnecessary because limestone is a limestone. The properties has more than it requires. Its a hard rock. In fact it took us 3 weeks to remove the limestone at layer B. The road is 500m x 7m wide.

My question is, is it necessary to remove the limestone and replace it with 300mm - Engineered Backfill Material.

RE: Replacing hard subgrade with another material like engineered backfill material

There would be no strength advantage in removing hard limestone. Is it possible that pavement underdrainage is the issue? Insisting on a specified cross-section without reason is ignorant.

RE: Replacing hard subgrade with another material like engineered backfill material

"The owners representative insist we must follow the design and disregard the actual site condition."

Did the owner clarify what part of the design you are not following? Seems to me if the limestone meets the subgrade requirements listed above then you have met the design.

RE: Replacing hard subgrade with another material like engineered backfill material

Could it just be a contractual matter? Maybe the owners rep does not want to carry the risk of accepting a change to the design, even though you are confident the adjustment to the design is justified.

Or maybe the owners rep is the contractors buddy and is just helping the contractor get the full worth of work tongue

RE: Replacing hard subgrade with another material like engineered backfill material

Item B is "aggregate base course". Limerock is an aggregate base course....at least in my area (and a very good one). Agree with hokie66. Ignorance is a poor designer!

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