# A State-of-the-Art Review on the Study of the Diffusion Mechanism of Fissure Grouting
## 1 Introduction  
In recent years, with the improvement in the level of engineering and construction, research on the optimization of grouting methods and their effects has become increasingly urgent. Significant progress has been made within the theoretical and technical development of grouting in terms of the grouting mechanism, grouting methods and technology, grouting materials, experimental technology, and other aspects. It is widely acknowledged that cracks are formed in rocks due to geological processes. In engineering applications, fissure grouting stands out as the most effective approach for addressing crack damage in rock masses. Therefore, studying the diffusion behavior of slurry for repairing this type of ailment holds immense significance. In terms of the diffusion mechanism of fissure grouting, current research primarily focuses on simulations and experimental investigations to explore the impact of parameters such as grouting material injection path, injection time, grouting pressure, and grouting volume on the diffusion mechanism. Furthermore, there is a growing emphasis on studying fundamental physical and chemical properties in domestic research, including aspects like grouting material viscosity [1, 2, 3, 4], surface tension [5, 6], ionic concentration [7], pH [8, 9], etc. In engineering practice, the grouting process involves the complex distribution of rock fissure structures and various types of slurry flow, resulting in a highly intricate diffusionmode of slurry within rock fissures. To investigate the diffusion behavior of slurry in rock fissures, numerous scholars, both domestically and internationally, have conducted extensive studies on the diffusion mechanism of polymers. [PERSON] et al. [10] studied the flow of porous fissure media using an equivalent permeability tensor in the equivalent continuous medium model. This model accurately describes the slurry diffusion trend in rock fissures at a macroscopic level but not the diffusion process itself. [PERSON] et al. [11] investigated the diffusion mechanism of fissure grouting using a step-by-step calculation method and partially discovered the diffusion mechanism of dynamic fissure grouting. [PERSON] et al. [12] proposed a grouting-process modeling technique that incorporates fluid-structure coupling, generates more realistic values for fissure apertures based on aperture-trace length relationships, and establishes numerical models to simulate fluid dynamics as well as structural deformation within fissured rock masses. These aforementioned methods are theoretical approaches put forth by scholars; additionally, some researchers have conducted experiments to study the interaction between fissure media and grouting materials, yielding significant findings. [PERSON] et al. [13] developed a visual fissure constant-pressure grouting test system that includes pressure supply equipment, constant-pressure pumping equipment, fissure simulation equipment, and monitoring equipment. This system can create a specific fissure network, simulate the grouting flow process, and investigate the grout-water/gas displacement mechanism in fissured rock masses. [PERSON] et al. [14] presented a sequential diffusion coagulation (SDS) method that considers the spatiotemporal evolution of slurry viscosity. They examined the slurry diffusion process at different flow rates using the SDS technique and discussed the effects of flow rate on grouting pressure, counter-current diffusion distance, and diffusion behavior. The research demonstrated the usefulness and feasibility of investigating the slurry diffusion mechanisms of large fissures on an engineering scale. [PERSON] et al. [15] conducted a true triaxial mechanical state freeze-thaw rock mass fissure grouting experiment. They performed computed tomography (CT) and scanning electron microscopy (SEM) tests on the grouted specimens to investigate the grout diffusion mechanisms of different grouting materials in freeze-thaw rock masses.