Study on Parallel Bond and Smooth Joint Dual Model Parameter Calibration of Mechanical Properties of Shale Under Pressure

Employing a rational numerical model to characterize the compressive mechanical properties of shale is highly significant for large-scale shale-related engineering demonstrations. By analyzing the effects of the Parallel bond and Smooth joint model parameters on shale macroscopic mechanical properties, a rational Parallel bond and Smooth joint dual-model mesoscopic parameter calibration method is developed. The superiority of this calibration method in simulating the mechanical properties and failure modes of shale compression is verified by fitting the uniaxial compression test data of shale samples with various inclination angles. The results show that in the Parallel bond model, the mesoscopic particle’s and bond’s elastic modulus ( \(E^\ast\) $E^{*}$ , \(\overline{E}^\ast\) ${\overline{E}}^{*}$ ) have a greater influence on the macroscopic elastic modulus, the mesoscopic cohesion and tensile strength ( \(\overline{c}\) $\overline{c}$ , \(\overline{\sigma }_c\) ${\overline{\sigma }}_c$ ) have a greater influence on the peak intensity, and in the Smooth joint model, the tangential stiffness \(k_s\) $k_s$ and tensile strength \(\sigma_c\) ${\sigma }_c$ of the joint significantly influence the stress–strain curve pattern; compared with the single Parallel bond model, the Parallel bond and Smooth joint dual-model mesoscale parameters are used to calibrate the elastic modulus and peak strength of the sample, and the simulation results of compression failure modes are in good agreement with the test results. The fitting applicability of this calibration method to the degraded shale sample is weaker than that of the original sample, which is related to the uneven degradation distribution and the formation of extremely weak surfaces of shale.