Shale and Weathered Rock Earth Pressures

[structgeotec]

I need a little guidance as to how to design a 12' cut on
shale with an RQD 7 and below 10' RQD is 45
I cant find to much literature as to designing retaining walls on rock
or shale.
Do I just assign a high Phi value like 45 to shale and a unit weight of 140 PCF
to make it work and find a Kp and Ka?

 

[PEinc]

RQD has nothing to do with the bedding angle of the rock. You need to consider if there is the possibility of a rock slide (wedge failure) into the excavated site. Rock slide pressure could be more than active earth pressure calculated with guesstimated "soil" properties. Rock mechanics and soil mechanics are different.
What you need could range from nothing to rock bolts to rock bolts with WWF to rock bolts with shotcrete. It all depends on the bedding, RQD, and weathering.

http://www.PeirceEngineering.com

 

[tsek]

Please provide rock core pictures. I can get you some loading.