Shear Strength Unsaturated Clay-Temporary Slope

[moe333]

Temporary slopes (stand-up time is several weeks) up to 20-30 feet high are proposed in unsaturated clay soils, with a moisture content of about 10-20%. Torvane/Pocket Pen. indicates Su of clay is stiff to very stiff. Phi=0 analysis is not really valid for unsaturated soil, and effective stress analysis using direct shear results run saturated is probably very conservative as it neglects negative pore pressures. Any suggestions in what shear strength to use for temporary slope stability analysis?

 

[GeoPaveTraffic]

Why not just use the values from the pocket pen and torvane tests. Additionally, you could run some unconfined compression and/or Q tests.

 

[DRC1]

If the clay is stiff, drainage will be slow. use undrained conditions for initial and drained conditions for final (in stiff clays, drained strengths can control. If you can do some testing it is better than pocket pens. 30 ft slope is prety high. If it goes, it can go quick. I like U-U with pore pressure measurements. If you can't find a local firm, check with your local university. When I was a grad student, we used to do a lot of soil testing for local firms.