Long-term accumulated deformation and phase transformation of K0-consolidated calcareous sand under wave-induced cyclic loading

Accumulated deformation induced by cyclic wave loading is an important factor affecting the long-term serviceability of calcareous sand foundations beneath artificial-island revetments. However, the evolution and governing mechanisms of accumulated deformation in calcareous sand under engineering-relevant initial anisotropic stress conditions remain insufficiently understood. Accordingly, drained cyclic triaxial tests with constant confining pressure were conducted on K 0 -consolidated saturated calcareous sand. The effects of initial mean stress ( p 0 ), initial static stress ratio ( η c ), cyclic stress ratio ( ζ ), and relative density ( D r ) on the dynamic response characteristics were systematically studied, including the accumulated axial strain ( ε 1 acc ), accumulated axial strain rate ( ε ˙ 1 acc ), accumulated volumetric strain ( ε v acc ), accumulated volumetric strain at the phase transformation ( ε v,p acc ), accumulated deviatoric strain ( ε q acc ), and particle breakage. The test results indicate that: (1) With increasing ζ and η c , ε 1 acc increases significantly, whereas an increase in D r effectively suppresses its development; the influence of p 0 on ε 1 acc is relatively limited. (2) Both ε 1 acc and ε ˙ 1 acc exhibit an evolutionary characteristic of rapid development initially followed by gradual stabilization. (3) ε v acc undergoes three distinct stages: initial contraction, phase transformation, and stable dilation. An empirical formula linking ε v,p acc to ζ , p 0 , and the void ratio ( e ) was proposed. Furthermore, the phase transformation state line (PTSL) was established in the e -( p / p a ) 0.7 plane. Its position depends strongly on the initial void ratio ( e 0 ), and it lies below the critical state line (CSL). (4) ε q acc far exceeds ε v acc , reveals a deviatoric-strain-dominated mechanism of long-term deformation in calcareous sand subjected to one-way non-reversal cyclic wave stress paths. (5) Significant particle breakage did not occur under the simulated test conditions; instead, cyclic wave loading primarily induced inter-particle rearrangement and fabric adjustment. (6) Finally, an explicit prediction model for ε acc 1 was developed, whose predictions agree well with measured data.