Observations during static and cyclic undrained loading of dense Aalborg University sand no. 1

Offshore structures are subjected to cyclic loading, which is one of the most important factors in the foundation design. Cyclic loading lead to complex soil response in undrained conditions. In this paper dense Aalborg University sand no. 1, ID = 90 %, is investigated performing a series of monotonic and cyclic triaxial tests. The post-cyclic strength is tested in the specimens that did not fail during the cyclic test.

Dense sand under undrained conditions is found to have more strength than in drained. An increase of 29 % in the shear strength of the soil due to cyclic loading is observed. Soil strength and stiffness are found to change depending on the type of loading applied.

Effective friction angle is found to be changing during various phases of loading. Linear Mohr Coulomb model could potentially be sufficient for modeling the full spectrum of dense sand behavior if extended with a changing friction angle following the examined patterns of response.

A total stress path based material model is presented in this paper.