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Power-law relationship between joint spacing and bed thickness in sedimentary rocks and implications for layered rock mechanics

2021; Elsevier BV; Volume: 150; Linguagem: Inglês

10.1016/j.jsg.2021.104413

1873-1201

Shaocheng Ji, Le Li, Denis Marcotte,

Seismic Imaging and Inversion Techniques

Fracture spacing (s) distribution and its dependence on bed thickness (t) are investigated for opening-mode joints in sandstone interlayered with shale in the Sainte-Anne des Monts area (the Gaspé Peninsula), Quebec, Canada. The s values of cross joints, which extend across intervals between long parallel systematic joints and abut these joints at about 90° angles, are consistently larger than those of systematic joints by a mean factor of 1.81. The s-t relationship follows a power law: s = mt1-1/k, where m equals half the ratio of layer tensile strength to interface shear stress, and k is the Weibull modulus. The m value is significantly larger for cross joints than systematic joints, indicating that the interfacial shear stress was direction-dependent during the deformation. The Weibull modulus of sandstone was larger during the formation of systematic joints than that of cross joints by a factor of ~1.2, indicating that the number and size of flaws in a unit of volume of the sandstone increased during progressive deformation. Furthermore, the compilation of s-t data from the literature yields: m = 2.53 ± 2.12 and k = 3.09 ± 1.24 for sandstones, and m = 3.53 ± 3.11 and k = 3.54 ± 1.33 for carbonates. The analysis also raises doubt about the existence of real joint saturation in sedimentary rocks.