Mixed face road subgrade in bedrock 2

[jpoha]

I am working on a roadway project which will include cuts in bedrock on the order of 50 ft high in some areas. The bedrock is significantly jointed and groundwater is present in the bedrock.

I typically recommend pavement underdrains in such cases. However, for a "mixed face" condition, where half the road will be in a rock cut and half will be newly placed fill, should there be any special considerations for subbase materials or preparation of the rock and fill subgrades at the interface point? For instance, should extra bedrock be excavated to provide a smooth transition, rather than leaving a sharp drop off? Is this even a concern?

Also, are there any special drainage considerations? I would recommend an underdrain along the cut side. Should an underdrain be recommended along at the interface point, or at the bottom of the fill zone?

Any suggestions and/or experience would be appreciated.

 

[Focht3]

I'd undercut and provide a high quality underdrain system beneath the proposed pavement. Sharp transitions are a bad idea in general -



Please see FAQ731-376 for great suggestions on how to make the best use of Eng-Tips Fora.

 

[BigH]

Don't know where you are but maybe one of the Canucks can get ahold of the British Columbia Standard Drawings. If I remember correctly, they have detailed sections for what you are talking about.

I have seen in some sections where you actually undercut the bedrock (even if all bedrock) by 300mm or so and place granular layer (drainage) that can be in direct contact with a drainage layer/side under the fill or trench if all in rock. Then the road pavement can go on top. The granular filled undercut also gives some cushion.