Long-term behaviour and degradation of calcareous sand under cyclic loading

Calcareous sand has been used as the main filling material in numerous reef constructions. Therefore, understanding its long-term dynamic engineering geological characteristics under cyclic applications of traffic or wave loading is crucial to the design and prediction of the serviceability of reef infrastructures. Considering this, seven monotonic triaxial tests and 33 high-cycle (25,000 cycles) drained triaxial tests were conducted on calcareous sand with various mean effective stresses (p') and cyclic stress ratios (sigma). The results show that the development of the accumulated axial strain (epsilon(acc)(1)) has a strong correlation with the positional relationship between the cyclic stress path and critical strength line (CSL) or static strength envelope (SSE) in the p'-q plane. The critical cyclic stress ratio.c, that represents the cyclic stress path reaching the CSL, is proposed. When sigma>sigma(c), the growth rate of epsilon(acc)(1) with. increases drastically. Moreover, when the cyclic stress path approaches the SSE, epsilon(acc)(1) enters an incremental collapse state. The increase in p' diminishes the dilatancy of the volumetric strain ev. However, this response of ev reverses from decreasing to increasing with increasing sigma. The resilient modulus (M-r) increases with the number of cycles (N) due to the initial densification. If epsilon(v) dilation occurs, M-r will decrease with N as particles lose contact. A single parameter for the cyclic stress path ratio (psi) considering the effects of p', xi, and SSE is proposed. Additionally, empirical formulas for calculating the ultimate epsilon(acc)(1) and M-r are established. Furthermore, particle degradation significantly worsens epsilon(acc)(1) and epsilon(v), but has a more profound effect on the compressibility of epsilon(v). This degradation is also detrimental to M-r. A certain deviation trend of the predicted values from the measured values is found to correspond with the relative particle breakage.