# Application of Microbially Induced CaCO\({}_{3}\) on the Reinforcement of Rock Discontinuity
## 1 Introduction  
The natural flaws found in rocks, such as bedding planes, fissures, and joints, play a significant role in influencing the chemical composition, seepage conditions, stress fields, and shear strength of rock masses [1; 2]. The stability of a rock mass is mainly controlled by its joints, and failure in this area can have catastrophic consequences [3]. Therefore, it is essential to focus on the treatment and reinforcement of rock joints to prevent disasters. Current leading prevention techniques include fully grouted rock bolts under aerodynamic effects [4; 5], inflatable and yielding bolt reinforcement [6], rock bolts reinforcement [7], new polymer reinforcement [8], silicate resin rock reinforcement [9], organomineral resin injection reinforcement of soft rock [10], tailing reinforcement by MICP [11], and gold mine tailing reinforcement [12]. The abovementioned strengthening techniques can enhance the shear strength parameters of rock masses to a specific level and reduce potential disasters. However, there are also some drawbacks, including poor durability, high energy consumption, high cost, and high pollution emissions [13]. To address these drawbacks and improve durability while reducing costs, it is crucial to develop and research a novel reinforcement technique forjointed rock masses that is environmentally friendly and economically feasible [14]. As a result, microbially induced calcium carbonate precipitation (MICP) technology has been utilized for soil and rock reinforcement due to its good injectivity, cost-effectiveness, and environmental friendliness [13; 15; 16]. MICP technology utilizes a microbial mineralization process to produce inorganic compounds that form cement-like gelling materials. These gelling materials strengthen jointed or broken rock masses [17]. The principle of the MICP method involves utilizing urease concealed by bacteria to produce carbonate particles in a non-acidic environment, which are then mixed with calcium ions to create crystals of cemented calcium carbonate [1; 18]. Following in-depth research into the MICP technique, it has made significant contributions in the field of soil and rock engineering, such as rough crack repair [19], earthquake liquefaction control [20], fresh river sand and silt reinforcement [21; 22], erosion protection of sandstone and sand [23; 24], and the improvement of the disintegration resistance and mechanical properties of residual soil [25]. Many studies, including papers and patents, have utilized MICP technology to repair concrete cracks of varying widths and shapes [26; 27; 28; 29; 30; 31; 32; 33]. The impermeability of the repaired cracks has been improved to different extents. The microbial grouting technique has also been used to improve the permeability constant of fractured limestone and phosphogysum material [17; 34]. In addition, the MICP technique can be used to repair cracked sandstone and granite [13; 35]. [PERSON] et al. [36] selected _Sporosarcina pasteurii_ to reduce the porosity of fractured yellow sandstone. [PERSON] et al. [37] investigated the influences of crack inclination angle, bacterial concentration, crack opening, and crack roughness on the fracture permeability of transparent rocks through four seepage experiments. The authors found that the permeability of the fracture filled with microbially induced CaCO rose as the crack inclination, opening, and roughness increased first and then decreased. [PERSON] et al. [38] found that the unconfined compressive strength (UCS) of a low-strength sandstone can be improved significantly with MICP, while this technique cannot effectively improve the mechanical properties of high-strength sandstone. These results provided a solid foundation for the reinforcement of fractured rocks by using the MICP technique. Furthermore, previous studies mostly improved the impermeability constant and unconfined compressive strength and reduced the porosity of different fractured rocks in natural environments.