This study studies the deformation characteristics of the diversion tunnel of Jinping II Hydropower Station in order to guarantee the safety of the excavation of a large-section soft rock tunnel with a depth of 1000 m and increased ground stress. Using field data, theoretical computations, and numerical modeling, the proper reserved deformation of a deep soft rock tunnel is investigated, taking into consideration the size, in situ stress, and grade of the surrounding rock. The study reveals that (1) The diversion tunnel’s incursion limit, which is typically between 20 and 60 cm, is serious; (2) The surrounding rock level > geostress > tunnel size are the influencing parameters of reserved deformation that remain unchanged while using the numerical simulation method, which is more accurate in simulating field conditions; (3) The west end of the Jinping diversion tunnel has a 30–60 cm reserved deformation range for the chlorite schist tunnel. The deformation law of a large-section, 1000 m-deep soft rock tunnel is better understood, and it also offers important references for high-stress soft rock tunnel engineering design, construction, and safety management.

Rock mass deformation is a time related process, especially for soft rock. Its deformation usually has a certain timeliness. Moreover, the deformation of surrounding rock is typically asymmetric. Therefore, it is of great significance to reasonably describe the time-dependent mechanical properties and behaviors of rock mass for practical engineering, especially when the actual engineering is a symmetric structure. Taking the chlorite schist section at the west end of the diversion tunnel of Jinping II Hydropower Station as the research object and introducing the characteristic that creep parameters attenuate with equal effect change into Burgers constitutive model used for numerical calculation, an improved Burgers model is proposed. Then, according to the actual situation of the project, the improved three-parameter H-K model, which is suitable for this study, is proposed by using the fractional calculus method. The effects of different factors on the rheological properties of soft rock tunnels are discussed. The results show that When K is equal to 1, creep is positively correlated with burial depth; When the burial depth H is 1500 m, the creep deformation is positively correlated with the horizontal geostress; The farther away from the working face, the greater the instantaneous elastic deformation release and the later creep displacement; After the tunnel excavation is stopped, the earlier the support is, the smaller the later creep deformation is; After excavation and support of the upper bench, the longer the stagnation time is, the more unfavorable the rheological deformation of the tunnel is.