Energy-based ue - εvp coupled incremental model of saturated marine coral sand subjected to cyclic loading

Abstract

Evaluating the stability of coral islands and reefs in dynamic marine environments, such as waves, tsunamis, storm surges, and earthquakes, is a critical scientific issue in the field of marine geotechnical engineering. Nansha coral sand was used as the study object, and stress-controlled drained and undrained cyclic-loading tests were conducted. The undrained excess pore-water pressure and the drained cumulative volumetric strain of saturated coral sand were determined at various non-plastic fine contents (FC), relative density (D_r), and cyclic stress ratio (CSR). The results indicated that cumulative volumetric strain (ε_vp) developed in coral sand via two modes: cyclic stabilisation and cyclic creep. Analyses revealed that when the potential damage coefficient (DP) × CSR < 0.05, ε_vp remained in the cyclic stabilisation mode and when DP × CSR > 0.05, ε_vp transitioned into the cyclic creep mode. Utilising cumulative dissipation energy as a linking factor showed an arctangent function relationship between the excess pore water pressure ratio (R_u) and ε_vp values of saturated coral sand with different FC, D_r, and CSR. This relationship was applicable to both stress- and strain-controlled cyclic-loading tests. Parameters m and n of the R_u–ε_vp function model increased with an increasing CSR. Additionally, an increase in the D_r or FC resulted in a decrease in m and an increase in n. Multiple regression analysis further revealed that model parameters corrected for compactness and cyclic stress levels exhibited distinct trends as the void ratio (e) increased. Specifically, CSR^α × m^Dr decreased, and CSR^1-α × n^Dr increased. Both parameters displayed a single power function relationship with e. Based on these findings, a coupled incremental model for the cyclic pore pressure and volumetric strain of saturated coral sand, based on energy conversion, was developed.