The structural properties of loess will change due to the shield construction. In order to explore the influences of variate structural properties on the mechanical properties of surrounding rock of shield tunnels, the structural parameters of stress ratio were introduced to modify the Mohr-Coulomb strength criterion and Fenner formula. By establishing the continuous conditions of force and displacement between loess strata and segments, the radius of plastic zone of surrounding rock was solved, and the analytical solutions were compared and verified. Finally, the influences of key parameters on the mechanical form of surrounding rock were analyzed. The results show that: (1) The calculation results of the Terzaghi surrounding rock pressure formula are between the upper limit and the lower limit of the analytical solution; (2) With the increase of the structure parameter of stress ratio, the corresponding plastic zone radius and surrounding rock pressure value are continuously decreasing; (3) With the increase of thickness span ratio, the radius of plastic zone decreases and the value of surrounding rock pressure increases. When the structural properties of loess are relatively strong, the analytical formula of surrounding rock pressure is applicable after the cover depth reaches a certain value; (4) The surrounding rock pressure and the radius of the plastic zone are approximately linearly positively correlated with the excavation radius.

In order to alleviate the crystallization blockage of drainage system caused by calcium leaching of tunnel shotcrete, based on the investigation of a variety of concrete admixtures, anti-alkali agent and nano-SiO₂, fly ash and nano-CaCO₃ were selected from two aspects of consuming free Ca(OH)₂ and filling concrete pores, for indoor single-mixing test. From four aspects of the crystallization of the drainage pipe, the concentration of calcium ion in the leaching solution, the change of the flow rate of the leaching solution and the total amount of calcium leaching calculated, the admixture with better effect of reducing calcium leaching and crystallization and its optimal dosage were selected through the intra-group comparison between different admixtures and the comparison under different dosages of the same admixture in the test. The results show that: anti-alkali agent with 9% dosage has the best effect of the resistance of calcium leaching and crystallization in the aspect of consuming free Ca(OH)₂; nano-CaCO₃ with 6% dosage has the best effect of the resistance of calcium leaching and crystallization in the aspect of filling concrete pores. The results of the study can provide some reference for the prevention of the disease of crystallization blockage in tunnel drainage system.

In order to study the enhancement effect of different annular joint structures on the longitudinal stiffness of shield tunnel, the influences of section diameter on the longitudinal tension and compression, longitudinal shear and longitudinal bending stiffness of tunnel are calculated by equivalent continuous model. The longitudinal stiffness enhancement measures are related to the annular joint structure of segment. Additionally, the mechanical properties of nine annular joint structures are deeply explored by numerical simulation, and the annular joint structure with the best effect of enhancing the tunnel longitudinal stiffness is obtained by comparison. The results show that the diameter has little effect on the longitudinal tension and compression and longitudinal bending stiffness, but has a great influence on the longitudinal shear stiffness. The stiffness enhancement measures of the circumferential joint can significantly reduce the displacement of the segment and improve the tunnel longitudinal stiffness. The enhancement effect is: oblique bolt > bend bolt, positioning tenon > shear pin > concave tenon; at the same time, both the bolt type and the longitudinal stiffness enhancement measures have a great influence on the maximum shear stress of the bolt. The shear stress of the bolt is significantly influenced by the bolt type at vertical load and is significantly influenced by the longitudinal stiffness enhancement measures at horizontal load. Combining economy and effectiveness, when the joint bolt is a curved bolt, setting the positioning tenon is a relatively better choice.