# Model Test on Grouting Properties of Alluvial Filler Soil
## 1 Introduction  
The grouting technique is extensively applied in the fields of geotechnical reinforcement and waterproofing underground engineering. However, engineers are more likely to use empirical formulas when dealing with grouting problems due to a lack of understanding of the diffusion law of slurry and the strength characteristics of grouting soil. For economic consideration, it is significant to reveal the diffusion law of slurry and predict the increase in shear strength of grouting soil. The published literature has mainly studied the grouting mechanism and the slurry diffusion law by means of theoretical deduction [1; 2; 3; 4; 5; 6; 7], numerical simulation [8; 9; 10; 11; 12; 13], and model tests [14; 15; 16; 17; 18; 19; 20; 21]. In terms of theoretical research, [PERSON] et al. [22] presented a macroscopic model of cement grout flow in a porous medium based on the mass balance equations of the different components present in the grouted medium as well as on a general phenomenological filtration law. [PERSON]'s research focuses only on the situation of radial flow filtration. [PERSON] et al. [23] developed an analytical model to estimate the fracture grouting process in sand. The results provided a guideline for assessing the parameters that affect the fracture process. However, the assumption that the complex shape of a fracture in sand is simplified to a plane or a tube In terms of numerical simulation, a series of numerical simulations have been conducted to assess the capability of compensation grouting modeling [24]. Based on an orthogonal test, [PERSON] et al. [25] proposed a new model for grouting simulation. It also needs to be mentioned that numerical simulation methods can be time-consuming and usually require a larger number of input variables, some of which should be estimated or assumed if they are not available at hand. A distinct advantage of the model test methods lies in the fact that the test data can provide meaningful physical insight into the governing parameters and also offer direct design data for grouting engineers. Nevertheless, only a few studies have been conducted to study the law of grouting diffusion and diffusion radius by grouting model tests. For instance, [PERSON] et al. [26] carried out a small-scale model compaction grouting test and came to the conclusion that the shape of the injected grout bulb is a function of overburden pressure. [PERSON] et al. [27] conducted a grouting model test to study the slurry flow and transport with filtration in porous media, which was used to analyze large-scale grouting. In [PERSON]'s et al. [23] study, laboratory experiments were carried out to investigate the mechanisms present during compensation grouting in sand. The results show that more cement in the grout results in a thicker filter cake and, therefore, higher injection pressures and shorter and thicker fractures. In order to study the influence of pressure filtration on tip improvement and provide insight into the influence factors of pressure filtration, [PERSON] et al. [28] conducted a comprehensive series of laboratory model experiments. The test results indicate that the velocity of pressure filtration is determined by the velocity of water through clay. [PERSON] et al. [29] carried out a small-scale model compaction grouting test and obtained the conclusion that the curves of both injection pressures versus time and injection rate versus time showed a wavelike relationship. Up until now, the diffusion law of slurry and the characteristics of grouting soil have been studied by a single analytical or numerical method. While research on grouting model tests is relatively rare, In order to gain a deeper and more thorough understanding of the diffusion law of slurry and the characteristics of grouting soil, the grouting model test was carried out in this study to investigate the distribution and diffusion law of slurry in alluvial filler. The strength characteristics of grouted soil were first studied by a soil test and a dynamic penetration test.