| Summary: | The effect of capillary water caused by heavy rainfall and groundwater level fluctuations can induce the erosion and collapse of island reef coral sand foundations. Here, the effects of water content (<i>ω</i>) on the shear strength parameters of coral gravelly sand are analyzed at the macro and micro scales by laboratory consolidated-drained triaxial compression and nuclear magnetic resonance tests. Furthermore, particle breakage characteristics of coral gravelly sand under the static load are discussed. With increasing <i>ω</i>, (1) the internal friction angle increases slightly (<1°) then decreases; (2) the apparent cohesion is more sensitive to the change in the <i>ω</i>; (3) with an increase from 5.4% to 21.3%, the bound water content remains almost unchanged; (4) the capillary water content is the main factor impacting the apparent cohesion; (5) the increase in free water content is the internal cause of the decreasing internal friction angle of coral gravelly sand with <i>ω</i> > 11.1%; and (6) the particle breakage increases, and there is an approximately linear relationship between the median particle diameter (<i>d<sub>50</sub></i>) and relative breakage index (<i>Br</i>). The established physical model can reflect the influence of water content and plastic work and describe the evolution law of particle breakage.
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