Effect of gradation on confined compression and creep of calcareous sand and the coefficient of earth pressure at rest

In the study, lateral compression tests and multi-level creep tests were conducted on calcareous sands with different gradations using a tailor-made model box. The compression and creep deformation, particle breakage, internal stress evolution and the variation of the coefficient of earth pressure at rest K0 under different stress levels for calcareous sands were investigated. It reveals that, under the same loading conditions, the compression deformation, creep deformation, creep rate and K0 decrease as the coefficient of uniformity Cu of the calcareous sands increases. This can be attributed to the rearrangement of particle positions and particle breakage. As Cu increases, the content of fine particles increases, filling the voids between the relatively large particle skeletons. This can enhance the particle interlocking and suppress the particle rearrangement and breakage, which in turn leads to reduced deformation and K0. As the vertical stress increases, significant particle breakage occurs, resulting in an increasing lateral deformation of the sample, which induces increased lateral stress and a corresponding elevation in K0. Additionally, particle breakage alters the contacts between particles, intensifying stress redistribution. Consequently, the distribution of vertical and lateral stresses within calcareous sand transitions from a Weibull distribution to a Gaussian distribution.