Nonlinearity of Soil Stress-strain Response from Laboratory Studies

Nonlinearity of clay soils based on the original data from laboratory studies is discussed. The presented new results of soil stiffness and damping ratio obtained in triaxial testing with small strain measurement using local Hall effect transducers, resonant column and torsional shear testing. Results of different tests are in good agreement demonstrating that threshold strain beyond which soil nonlinearity is triggered is about 0.02-0.03% and may be related to the displacement magnitude of the order of 0.01-0.03 mm which is comparable to predominant particle size in the soil. This idea can provide a basis to a new approach to understanding the nature and regularities of soil nonlinearity. It is also shown that damping is not only frequency dependent but is rather strain-controlled phenomenon.