Volumetric Threshold Shear Strain for Cyclic Settlement

The volumetric cyclic threshold shear strain for cyclic settlement, γ\Dtv\N, is evaluated for seven different sands and clays at different degrees of saturation, \iS, from the results of 11 Norwegian Geotechnical Institute-type direct simple shear, multistage cyclic settlement tests. Each test included several cyclic strain-controlled stages at cyclic shear strain amplitudes, γ\dc, slightly smaller and slightly larger than γ\Dtv\N, such that γ\Dtv\N could be evaluated from each single test. At γ\dc γ\Dtv\N they did. The data show that γ\Dtv\N is larger for clays than for sands and that it generally increases with the soil’s plasticity index (PI). For example, γ\Dtv\N≈0.01–0.02% was obtained for sands and γ\Dtv\N≈0.04–0.09% was obtained for clays having PI≈30. A rather consistent γ\Dtv\N versus PI correlation for cyclic settlement is presented. No obvious trends were found between γ\Dtv\N and \iS and vertical stress.