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Tunnelling or undertaking below-ground construction in squeezing ground can always present many engineering surprises, in which this complicated geology bring a series of tunnelling difficulties. Obviously, if the major affecting factors and mechanism of the structure damage in these complicated geological conditions are determined accurately, fewer problems will be faced during the tunnel excavation. For this study, reference is made to four tunnel cases located in the Qingling-Daba mountainous squeezing area that are dominated by a strong tectonic uplift and diversified geological structures. This paper establishes a strong support system suitable for a squeezing tunnel for the purpose of addressing problems exhibited in the extreme deformation of rock mass, structure crack, or even failure during excavation phase. This support system contains a number of temporary support measures used for ensuring the stability of tunnel face during tunnelling. The final support system was constructed, including some key techniques such as the employment of the foot reinforcement bolt (FRB), an overall strong support measure, and more reserved deformation. Results in this case study showed significant effectiveness of the support systems along with a safe and efficient construction process. The tunnel support system proposed in this paper can be helpful to support design and provide sufficient support and arrangement before tunnel construction in squeezing ground.

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Self-gravity is one key parameter for behavior characterization of grout permeation and diffusion.is study proposes mathematical models for permeation grouting with consideration of grout self-gravity effect. e models concerning power law, Bingham, and Newtonian grouts are based on the generalized Darcy's law and spherical diffusion theory. In addition, a prediction model of grout concretion dimension used for Bingham grout was developed. An analysis of the injection pressure distribution law and a comparative evaluation of diffusion radius considering self-gravity effect using established models were conducted subsequently. Moreover, grouting experiments were performed to check and verify the prediction model. e experimental results showed that injection pressure decreases linearly with increase of diffusion radius for the power-law grout, while nonlinear decrease of injection pressure was confirmed in Bingham and Newtonian grouts in this case. ree grouts approximately diffuse in an "ellipsoidal" shape, and it is confirmed that the diffusion radius is closely related to grout self-gravity. e Newtonian grout produces the maximum diffusion radius compared with the other two grouts whether the gravity effects were considered or not. e grout quantity under a smaller water-to-cement (w/c) ratio exhibits a significant difference and undergoes two increasing stages, whereas the quantity simply tends to be stable after it reaches its maximum in terms of the larger (w/c) ratios. e constructed dimension prediction model agrees well with the experimental results, which can be helpful for design and assessment of the grouting scheme.