Impact of stylolites on the mechanical strength of limestone

- New UCS data on microporous limestone
- Unique set of data on the impact of stylolite on UCS of carbonates
- New petrophysical data on stylolite-rich carbonates
- New microstructural observations on stylolites
- Stochastic modelling of stress-induced damage in stylolite-rich carbonates

We performed a series of uniaxial compression tests on samples of microporous carbonates from the Paris Basin (Bure, France). Sedimentary stylolites are pervasive in these formations. We show that the porosity in the vicinity of the stylolites is always higher than that of the host rock. As a result, our new mechanical data reveal that samples with a stylolite are always measurably weaker with respect to the adjacent stylolite-free material. However, when present, the orientation of the stylolite (with respect to the direction of loading) does not result in any mechanical anisotropy. Numerical simulations using a 2D finite element code suggest that the weakening induced by the presence of a stylolite is mostly due to the higher porosity and the higher level of heterogeneity in and around the stylolite, while the absence of mechanical anisotropy is due to the roughness of the stylolite. While the presence of stylolites weakens carbonate rocks, stylolites only act as planes of weakness when their thickness exceeds a certain threshold (about 5 mm).