In order to solve the problem that shallow and small clearance tunnels are easy to cause city road to collapse and chapped, taking the Jinan Yuhan Road Tunnel under typical geological conditions as the research object, the stability criterion of the middle soil wall is determined using a mechanical model of the tunnel middle wall. A grouting test under different loads of undisturbed soil in the tunnel is designed, and numerical simulation of the grouting of the middle wall of different tunnel depths and spacing is performed. The results show that the stability of the middle wall of the shallow and small clearance tunnel is related to depth, spacing, and the physical-mechanical properties of soil. The physical-mechanical properties of soil change little after grouting reinforcement with the same final grouting pressure as the burial depth increases. The stability criterion curve of the middle wall of Yuhan Road Tunnel is obtained by the measurement results of grouting test samples, and the numerical simulation results obtained by the experimental parameters have a high degree of agreement with the theoretical curve. Based on the stability criterion curve, sectional grouting was performed in Yuhan Road Tunnel, and the soil around the tunnel was successfully reinforced.

Mud inrush disaster is a typical geological disaster during the construction of mountain tunnels, which may bring immense economic losses and is very harmful to the local environment. Permeation grouting is an important treatment method for mud inrush disaster, which has been wildly used in China. In this paper, a theoretical model of permeation diffusion of Bingham fluid considering gravity is presented. A set of visual permeation grouting experiment device was designed. The test results verify the new permeation diffusion model showing that the slurry is spherical diffusion, while the strip-shaped diffusion appears under the spherical diffusion. With the increase of grouting quantity, the spherical diffusion radius increases gradually. Meanwhile, both the number and radius of the stripshaped diffusion increases gradually. The regression analysis of grouting quantity of 30 typical test data shows that the degree of influence of the grouting quantity from big to small is: grouting pressure, permeability coefficient, and water-cement ratio. The statistics of the total grouting quantity and the grouting quantity of spherical diffusion indicate that the grouting quantity of strip-shaped diffusion accounted for about 50%, which shows the importance of strip-shaped diffusion in surrounding rock reinforcement. This new diffusion model has certain guiding significance for practice.

In the process of split grouting, soil will compress the surrounding soil under the action of expansion pressure, reduce the gap between soil particles. Based on this, the stress-strain relationship model describing the nonlinear compression characteristics of soil mass was established to simplify the dynamic development process of split grouting veins. Considering the loss of grouting pressure along the path, the corresponding relationship between the set value of the first sequence grouting circle cake pulse diffusion radius rmax1 and the set value of grouting pressure p0 was obtained, and the corresponding calculation method of grouting time was obtained. Under the condition that the previous sequence grouting changes the distribution direction of the major and minor ground stress, the corresponding relation between the secondary grouting diffusion radius rmax2 and the set value of grouting pressure p′0 and the calculation method of grouting time are obtained. The model test of split grouting is carried out, and the test results show that the vertical split grouting can be achieved by setting the target pressure and grouting time after the horizontal split grouting and the direction of the ground stress change, which verifies the rationality of the theory.

With the construction and planning of the Sichuan-Tibet Railway and the Strait Tunnel, the tunnel construction has further deepened into the former engineering geological forbidden area, and a large number of large buried depths and long hole line tunnels have emerged. The problems of extremely high water pressure, strong permeable strata, high ground stress, high ground temperature, and high active faults are becoming more and more prominent. As a direct means of geological disaster management, grouting can effectively change the physical and mechanical properties of the stratum, carry out anti-seepage reinforcement of the surrounding rock, ensure the safe development of resources, and greatly reduce the impact of a complex geological environment on engineering construction. This paper summarizes the research status and development trends of splitting grouting domestically and abroad in recent years, splitting grouting materials and equipment, numerical simulation calculation, and key technologies that need to be broken through. The development status and trend of key technologies of splitting grouting are analyzed from the above four aspects. The grouting theory, materials, equipment, and effects inspection methods are mainly analyzed and discussed. Based on the research and development of existing key technologies, it is of great significance to further deepen the research on grouting theory, innovate and optimize grouting technology, develop and prepare grouting materials, customize supporting drilling and grouting equipment, and quantitatively determine grouting effects to promote the sustainable development of tunnel grouting technology. This review can provide a new perspective and basic data for academic research in the field of grouting in geotechnical engineering.

Due to the hidden nature and complexity of the underground engineering rock body, the actual grouting process is mostly a black box operation, which makes it difficult to observe and control the splitting direction of the slurry vein, and the slurry vein splitting is difficult to be expanded according to the expected direction and length, therefore, it is especially important to clarify the splitting law, start splitting and diffusion law of the slurry vein during the grouting process to study the directional control mechanism of the splitting grouting slurry vein. Therefore, an array type 27-channel multivariate data monitoring true triaxial split grouting simulation tester is developed independently, which includes four parts: true triaxial grouting test platform, triaxial loading unit, digital grouting unit and information acquisition unit, and the system can be used to carry out split grouting simulation tests under different geostress conditions, and to study the split diffusion law of the grouting veins in the complex soil body.