Dynamic response and failure mechanism of ocean coral reef limestone under high strain rate loading

As the primary bearing stratum of ocean coral reefs, coral reef limestone (CRL) is inevitably subjected to various dynamic external loads. A comprehensive understanding of the dynamic mechanical properties of CRL is crucial for ensuring the integral stability of coral reefs. In this study, a series of dynamic compression tests on the representative shallow CRL specimens were conducted using the Split Hopkinson Pressure Bar (SHPB) system. The dynamic mechanical characteristics of the CRL specimens were investigated in terms of the dynamic compressive strength, energy dissipation, fracturing process and fragmentation characteristics. A more significant rate-dependence in the compressive strength of CRL than other terrestrial rock materials was observed as the dynamic increase factor (DIF) tripled with the strain rate increasing from 98 s-1 to 246 s-1. This phenomenon was mainly attributed to the highly heterogeneous and complex pore structure within CRL. With the aid of the digital image correlation (DIC) technique, the progressive fracturing process of CRL were analyzed. Results showed that the enhancing effect of strain rate on strength promoted the emergence of more microcracks and accelerated the fracturing process of CRL. Moreover, the increasing strain rate intensified the degree of fragmentation. Statistical analysis of the fragments demonstrated that as the strain increased, CRL specimens produced more small-size fragments and had a higher fractal dimension of fragmentation. Thus, the failure of the CRL specimens at high strain rates consumed more energy, resulting in the absorbed energy density increasing from 0.13 J/cm3 to 0.24 J/cm3. These findings can provide guidance for protective designs in reef engineering.