R Lancellotta

Monotonic and Cyclic Loading Behavior of Two Sands at Small Strains

The shear modulus of freshly deposited specimens of two different sands was measured in a resonant column (RC)-torsional shear (TOS) apparatus. The soil specimens studied included a calcareous, crushable, well-graded, coarse-to-medium sand containing about 2% fines (Quiou sand) and a silica, uniform, coarse-to-medium sand without fines (Ticino sand). A brief description of the apparatus, with particular attention to the facilities used for the monotonic loading condition, is given together with a concise literature review. The shear moduli of the two sands in cyclic dynamic tests (RC) were compared with those measured in static monotonic loading torsional shear tests. It is shown that at small strains of less than about 0.001%, the shear moduli of the Ticino sand obtained from the dynamic tests and the static monotonic loading tests are the same, which means that the behavior of the sand at these very small strain levels is strain-rate independent and recoverable, namely elastic. In the case of Quiou sand, the shear moduli at small strains obtained from the dynamic tests are 20% greater than those from the static monotonic loading tests. The authors believe this difference is due to the sand crushability. It is also shown that the strain level dependency of shear modulus at larger strain levels is smaller under cyclic loading conditions than in monotonic loading conditions. The effects of precompression and cyclic prestraining are also examined.