The high water content of the surrounding rock in loess tunnels will lead to the deterioration of rock strength, causing deformation and damage to the initial support structure and thereby affecting safety during construction and operation. This article first analyzes the strength characteristics of loess under different water contents through indoor physical and mechanical tests. Secondly, based on numerical simulation results, the ecological environment, and design requirements, the water content threshold is determined. Finally, a reinforcement scheme combining surface precipitation measures and curtain grouting measures is proposed, and the reinforcement effect is analyzed based on on-site monitoring data. The results show that as the water content of loess increases, the cohesion, internal friction angle, and elastic modulus of the surrounding rock all decrease, leading to an increase in the sensitivity of the surrounding rock to excavation disturbances and a deterioration in strength. During the construction process, it shows an increase in the vault settlement and sidewalls’ convergence. During the process of increasing the distance between the monitoring section and the palm face, the settlement and convergence of the tunnel show a rapid growth stage, slow growth stage, and stable stage. The water content threshold is determined to be 22%. The reinforcement scheme of combining surface precipitation measures with curtain grouting measures not only meets the requirements of the ecological environment but also makes the settlement and convergence values lower than the yellow warning deformation values required by the design.

The tunnel’s cast-in-place inner drainage ditch is a thin-walled structure, and its construction joints are weak points in terms of waterproofing. Water leakage often occurs due to concrete cracking at the construction joints of the drainage ditch and the failure of waterproofing measures. Buried rubber waterstops are commonly used for waterproofing tunnel drainage ditch construction joints. Therefore, it is essential to understand the waterproofing function and mechanical properties of rubber waterstops at tunnel drainage ditch construction joints. Based on the waterproofing mechanism of waterstops and combined with numerical simulation, this paper analyzes the failure range and mechanical characteristics of buried rubber waterstops at construction joints in tunnel drainage ditches under different structural deformations, bonding forces, installation angles, and water pressures. The results indicate that, the shear resistance of the waterstop is superior to its tensile strength; the area of interface bonding failure decreases as the interface bonding strength increases; the stress in the concrete structure increases sharply with increasing angle; Under the simplification that the hydrodynamic pressure is equal to the hydrostatic pressure, the reaction force of the groove decreases gradually as the water pressure increases, and the water pressure is mainly borne by the concrete structure.