Red bed slopes in the southwest of China are associated with a grant number of geological hazards, such as landslides, mud‐rock flows, and rock blocks falling, which are vital problems in geotechnical engineering. The damage can be induced or triggered due to a series of human and environmental activities, such as excavation, concentrated or long‐term rainfall, earthquake, and fluctuation of groundwater level. According to the field observations and geological exploration results, a small‐scale landslide was observed on January 10, 2016, after excavation along XiaoMo highway in Yunnan Province. A numerical model in actual size using GeoStudio software based on this typical red bed engineering slope was established in this study. Back analyses and laboratory tests were used to obtain the mechanical parameters of the geomaterial inside the slope. The historic rainfall data of Mengla County from July to September in 2016 was utilized as the flux boundary in analyzing the seepage variation features and the stability of the engineering slope in the rainy season. One major tension crack was set in the shallow region of the silty clay according to the geology survey to perform the disturbance of excavation on the geomorphology of the slope. Attempts were made to establish the anisotropic permeability of the crack induced by the complex fillings, and differences in the hydraulic response between the cracking and completed slope during the rainfall process were discussed. The result shows that the factor of safety of the slope without crack before the rainfall is 1.076, and the slope is considered in the state of the critical limit equilibrium, which is in accordance with the previous state of the slope under real conditions. The pore water pressure variations of the monitor points in the shallow region of the completed slope present close compliance with the rainfall intensity subjected to different rainfall patterns, which also controls the distribution of the plastic zone in the slope after rainfall. The comparisons in the seepage field and plastic zone between the cracking and completed slope reveal that the crack can shorten the infiltration path effectively, and the higher the permeability coefficient in the vertical direction is, the larger the pore water pressure increasing zone is and the higher the underground water level is, which should be paid more attention in highway constructions.

Surrounding rock pressure is a crucial parameter in tunnel engineering design, and its calculation is a classic challenge. The surrounding rock pressure is influenced by geostress, but existing calculation methods often do not take into account the effect of geostress. In this paper, finite discrete element method (FDEM) is used to study the design values of tunnel surrounding rock pressure under different geostress fields. Firstly, a set of calibration methods for input parameters of FDEM is summarized based on previous studies. Then, taking a high-speed railway tunnel in IV-level surrounding rock as an example, the excavation-induced failure process of the tunnel under the influence of gravity stress field and geostress field is simulated using the FDEM. By comparing the results with those of the finite element method simulation, the rationality of applying FDEM to the simulation of tunnel excavation is demonstrated. Next, a calculation method of surrounding rock pressure design value based on FDEM is proposed by introducing tunnel displacement criterion, and its validity is verified by comparing with the results of the theoretical formula. Finally, the surrounding rock pressure design values under different geostress are analyzed by using this calculation method. The results show that there are significant differences between the gravity stress field and the geostress field in the maximum principal stress distribution, failure zone form and crack distribution. The geostress directly influences the design value of surrounding rock pressure. As the geostress varies from 4MPa to 12MPa, the corresponding design value increases from 49KPa to 1,288KPa, illustrating a quadratic relationship between them. With the corresponding design support force, the displacement of the surrounding rock is controlled within a reasonable range, ensuring the stability of the tunnel is maintained.

In the field of shield tunnels, the occurrence of uneven longitudinal settlement in segment linings has presented persistent challenges, including heightened risks of localized damage and water leakage. While the adoption of a secondary lining has been proposed as a viable solution to these issues, the question of how to select an appropriate construction time for the secondary lining, one that enables it to fully harness its load-bearing capacity while optimizing the tunnel’s overall stress and deformation characteristics, continues to be a pressing concern. To address this issue, this study established a three-dimensional longitudinal refined numerical model of double-layer-lined shield tunnel. In addition, the deformation degree of the segment lining was used as a time indicator to define the construction time for the secondary lining. Subsequently, an analysis of the impact of the construction time of the secondary lining on the longitudinal mechanical properties of the double-layer-lined shield tunnel is conducted through an assessment of tunnel longitudinal deformation and structural stress. The research findings indicated that the construction of the secondary lining improved the longitudinal deformation resistance of shield tunnels. Simultaneously, it led to a significant increase in the longitudinal shear forces within the segment lining and a notable reduction in longitudinal bending moments. Moreover, the construction time of the secondary lining played a pivotal role in these alterations. Considering the longitudinal force situations and load-bearing characteristics of the double-layer lining structure, it was determined that the optimal construction time for the secondary lining fell within the range of 20% to 40% of the total construction duration. In this scenario, the deformation and internal forces within the segment lining remained within permissible limits. Additionally, both the segment lining and the secondary lining were able to fully utilize their load-bearing capacities, ensuring the economic and safety aspects of the tunnel.