Liquefaction of sands during earthquakes The cyclic strain approach

The paper discusses a new method to evaluate the liquefaction potential of sands during earthquakes using the cyclic strain approach. This is an alternative to the customary cyclic stress approach to the problem. The new method is based on experimental and analytical results which show that cyclic shear strain is a better parameter than cyclic shear stress for defining the pore pressure buildup of saturated sands during undrained cyclic loading. Evidence is presented which demonstrates that sample fabric has significantly less effect on the results of strain-controlled than on those of stress-controlled laboratory tests. Furthermore, it is suggested that the influence of other factors which affect the results of stress-controlled tests is significantly reduced or disappears when strain-controlled tests are performed. A key factor in the proposed approach is the use of the threshold cyclic shear strain, γ t , which just generates an excess pore pressure. Some new theoretical and experimental evidence is presented to demonstrate the existence of the threshold, γ t ≃ 10 -2 %. This evidence also shows that the value of γ t is relatively insensitive to relative density and confining pressure.