Rock Mechanical Characterization of Epoxy-Based Grouted Sandstone

ABSTRACT: Studies have attempted to understand how cement grout penetrates and hydraulically seals fractured rocks. However, due to the characteristic limitations of grout, such as poor dispersion and bonding properties prompt the need for alternative grouting technologies in rock engineering. Furthermore, understanding how grout materials seal fractures and react to in-situ stress is currently insufficient. In this work, we explored the potential of epoxy-based material as a grout for fractured sandstone rocks and assessed its potential in modifying the overall rock strength. The epoxy-based cementitious material mixture was used for the pre-and post-grouting of fractured sandstones to evaluate the mechanical integrity through uniaxial compressive tests. In the results, the uniaxial compressive strength (UCS) of treated samples was altered with the grout material appearing to seal the rock fracture. The results also indicated that the grout treatment relatively increased the strength (UCS) of the grouted sandstone by (+2.4% UCS). Furthermore, imaging analyses suggest that the grout material can impact and alter the rock's microstructure and yield good material uniformity. This study provides a first leap in experimental investigations toward advancing eco-friendly reinforcement mechanisms of sealing fractured rocks and their impact on rock grouting. 1. INTRODUCTION Rock grouting is a geo-engineering technique that involves injecting grout materials into fractures, joints, and discontinuities in rocks to support reinforcement, reduce permeability and enhance stability (Liu and Sun, 2019; Liu et al., 2017). The grout can fill the fractures in rocks, causing the fractured rock to improve its bonding efficiency, thus enhancing the overall strength of the rock (Salimian et al., 2017; Oppong et al., 2023). Grouting can significantly strengthen rock fissures by reducing free void spaces and decreasing seepage in the grouted rocks (Li et al., 2020). It has also been proven to be an effective technique for preventing water inflows, which in turn helps to inhibit the weakening of fractured rock (Barton and Quadros, 2019; Zhou et al., 2023). This not only strengthens the rock's integrity but also ensures its reinforcement. Studies have demonstrated that grouting reinforcement can significantly improve the mechanical properties of fractured rocks, including strength and deformation resistance (Liu et al., 2017). Kikuchi et al. (1997) used an in-situ test to investigate the effects of grouting injection using a borehole expansion test, electromagnetic waves, and elasticity to predict the mechanical properties of sandstone and mudstone rocks containing weaknesses, and the findings revealed that grouting can significantly improve the strength of fractured rock. Zhao et al. (2016) examined the impact of grout infillings on enhancing the mechanical properties of pre-flawed rock, especially at lower inclination angles, and the study revealed that grout infillings can enhance the mechanical properties of pre-flawed rock and reduced the stress concentration by narrowing the micro-fracturing region. Sui et al. (2015) investigated the importance of grout penetration into connected fracture networks as a fundamental principle for achieving effective sealing efficiency and enhancing the structural integrity of fractured rocks. It was observed that the grout quickly propagated along the fracture boundaries and sealed the rock grains without spreading around the fractures upon solidification. However, due to the essential drawbacks of grout, such as poor dispersion resistance, bonding properties, mixture design and viscosity, injection pressure, yield stress, and in-situ stress an alternative technology for grouting fractured rocks is required (Mortazavi and Maadikhah, 2016).