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Seismic strength reduction in dry cemented sands?

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ckissick

Geotechnical
Jul 12, 2006
26
I'm doing slope stability analyses on a small slope. It's under a building and never gets wet. No groundwater. The soil is slightly cemented silty sand, phi=45, c=600. The FSs are very high, as I knew they would be, but the County wants me to do the analyses, anyway.

The static FS is 6.5. The seismic FS is 3.3, with c=600. I was wondering if I should reduce c due to cyclic loading. Are there any papers on the subject of cyclic loading on weakly cemented, dry sands? I believe Nick Sitar at Cal wrote on this topic, but can't find the papers.

Just for fun, I ran the seismic analysis with c=50, and got a FS of 1.1. But I think c should be much closer to the static value of 600.
 
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Both the phi and c values seem very high for a slightly cemented silty sand. As a starting point, I would try using 80% of the static strength. Try looking at the publication "recommended procedures for implementation of DMG special publication 117". For this type of material, I would use the peak shear strength from a remolded sample (sample remolded to the in situ moisture and density).
 
I meant to say peak "drained" or "effective stress" strength. The sample should be saturated during the test.
 
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