Micromechanics of inelastic compaction in two allochemical limestones

To investigate inelastic compaction in limestone we deformed in conventional triaxial configuration samples of two allochemical limestones: Indiana and Majella limestone with porosity of 14–16% and 30%, respectively. We described the microstructures associated with the damage evolution. Inelastic compaction in both limestones was associated with pore collapse that seemed to initiate from stress concentrations at the surface of a pore. Cataclasis appeared to develop preferentially around the macropores, in agreement with a recent study on a micritic limestone. Our new observations however showed that the spatial distribution of damage in the allochemical limestones can be complicated by its uneven partitioning among the allochems, micrite and sparite. In Indiana limestone, many allochems remain relatively intact even after the cement has undergone significant microcracking, with the implication that significant strength contrast exists between the allochems and cement. In Majella limestone, the asymmetry in damage intensity is not as pronounced, suggesting a less pronounced mechanical contrast between allochems and cement. In both limestones, significant mechanical twinning was observed in samples deformed to relatively high level of strain. We applied to our data a model, that treats a limestone as a dual porosity medium, with the total porosity partitioned between macroporosity and microporosity.