# Failure and Deformation Behavior of Underground Geo-Structures: Advances in Geomechanics
## 2 An Overview of Published Articles  
\"Influence of Preconditioning and Tunnel Support on Strain Burst Potential\" by [PERSON] et al. (contribution 1) addresses the significant challenge of strain burst hazard in deep underground environments. This study emphasizes the importance of assessing the probability of strain burst occurrence and implementing effective mitigation measures to ensure workplace safety. While various methods have been proposed to assess strain burst potential, uncertainties in rock mass properties and physical processes necessitate additional defense measures. This paper investigates the impact of shotcrete, rockbolts support, and destress blasting on strain burst potential using two-dimensional numerical models of circular tunnels. The results indicate that the implementation of mitigation measures reduces the occurrence of strain bursts, but the hazard level persists, especially in cases of serious overbreak hazards. The combination of support systems and destress blasting shows promise in mitigating strain burst events, but its effectiveness varies across different scenarios. \"Application of Image Processing in Evaluation of Hydraulic Fracturing with Liquid Nitrogen: A Case Study of Coal Samples from Karaganda Basin\" by [PERSON] et al. (contribution 2) investigates the microstructure and permeability evolution of coal following treatment with liquid nitrogen (LN2) for cryogenic fracturing compared to conventional hydraulic fracturing methods. This study utilizes high-resolution imaging techniques and image processing tools from the OpenCV Python library to analyze the 2D microstructure of bituminous coal samples before and after LN2 treatment. Digital images are processed to identify cracks and evaluate parameters such as crack density, total crack area, and average crack length. The results demonstrate a progressive increase in total crack area with longer freezing times and an increased number of freezing-thawing cycles. Crack density remains largely unaffected by freezing time alone but shows a significant increase after multiple freezing-thawing cycles. The study also highlights variations in crack density and number of cracks across different freezing times and cycles, with significant increases observed in certain treatment processes. Overall, the findings provide insights into the effectiveness of LN2 treatment for hydraulic fracturing in coal samples and demonstrate the utility of image processing techniques for analyzing microstructural changes in fractured materials. \"Interaction of Segmental Tunnel Linings and Dip-Slip Faults--Tabriz Subway Tunnels\" by [PERSON] et al. (contribution 3) addresses the behavior of segmental tunnel linings when intersecting with dip-slip faults, focusing on the Tabriz Subway Line 2 passing through the Baghmisheh Fault. Given the high costs of urban tunnel projects, understanding the performance of concrete structures under fault movement risks is crucial. This study employs advanced 3D numerical finite difference simulations with a plastic hardening constitutive model for soil to examine the behavior of straight and oblique segmented structures under large deformations. Fault-tunnel simulations are validated using centrifuge tests on segmental tunnels for normal faulting, showing a maximum difference of 15%. The results indicate that segmental structures outperform continuous structures during reverse fault movement, as they do not collapse but exhibit slight deformations. Among segmental structures, those with oblique joints demonstrate better behavior against faulting compared to those with straight joints. The findings suggest that utilizing oblique joints in segmental structures can enhance tunnel performance under fault movement conditions. \"Feasibility Study of Controlled-Source Electromagnetic Method for Monitoring Low-Enthalpy Geothermal Reservoirs\" by [PERSON] et al.