# Failure and Deformation Behavior of Underground Geo-Structures: Advances in Geomechanics
## 2 An Overview of Published Articles
\"Sensitivity Analysis of Wellbore Mud Pressure towards Anisotropic Shale Properties, Pore Fluid Pressure and Far Field Stresses\" by [PERSON] et al. (contribution 9) investigates the mud pressure required to maintain the stability of wellbores drilled in transversely isotropic shale. This is accomplished through sensitivity analyses conducted using both analytical and numerical modeling techniques, specifically employing the FDM (Finite Difference Method). The anisotropic strength of the Tournemire shale is interpreted using two distinct criteria: the Weakness Plane Model (WPM) and the modified Hoek-Brown criterion (HBm). The sensitivity analyses are performed on synthetic case studies, revealing varying trends in mud pressure predictions between the two criteria. Notably, the WPM and HBm may predict different mud pressures in certain scenarios, with some cases showing higher pressures with the WPM and vice versa. The HBm predictions are found to be more sensitive to changes in the anisotropy of far field stresses across all inclinations of the weakness planes. Conversely, the WPM occasionally predicts anomalously low mud pressures over a wide range of weak plane inclinations. Furthermore, the frictional component of strength exhibits a decrease with increasing pore fluid pressure for both criteria. However, the mud pressure predicted by the WPM demonstrates greater sensitivity to changes in frictional strength compared to the HBm. Given the change in trends observed with variations in the input data, caution is advised in the selection of the strength criterion. The paper suggests a simple solution for predicting safe and reliable mud pressure with a minimal number of laboratory tests, aiming to provide practical guidance for engineering applications in shale drilling scenarios. \"Application of a Finite-Discrete Element Method Code for Modelling Rock Spalling in Tunnels: The Case of the Lyon-Turin Base Tunnel\" by [PERSON] and [PERSON] (contribution 10) investigates brittle failure, or spalling, around excavations in hard rock masses with high in situ stresses. This phenomenon occurs due to the nucleation and growth of cracks induced by stress redistribution following excavation. Modeling this process is challenging, but the hybrid finite-discrete element method (FDEM) can capture emergent discontinuities associated with brittle fracturing processes by bridging the continuum and discontinuum domains. In this study, FDEM is applied using a commercial code to model brittle behavior around deep underground excavations, specifically focusing on the Torino-Lyon Base tunnel under three stress conditions. The results show that cracking occurs immediately after excavation, leading to extended spalling around the tunnel. This highlights the need for carefully designed support systems to prevent blocks from falling from the tunnel boundary. The findings are consistent with the previous literature, but this study reveals deeper spalling caused by gradual stress redistribution and shape changes. This emphasizes the importance of using a code capable of identifying crack propagation, opening, and the formation of loose blocks, which progressively alter the tunnel contour. Overall, this study demonstrates the applicability of FDEM in modeling brittle behavior around deep underground excavations and underscores the importance of accurately predicting spalling to ensure the safety and stability of tunneling operations. \"Improvements in Rock Mass Description for Stope Design by Geophysical and Geochemical Methods\" by [PERSON] et al. (contribution 11) delves into the critical aspect of stope design in mine planning, which aims to optimize ore recovery, minimize ore dilution, control production costs, and ensure safety. It presents the main findings of research aimed at introducing novel techniques for characterizing the ore body and surrounding rock mass before stope excavation. The research involves a comprehensive literature review and a survey of mining professionals to evaluate current stope design practices.