To address the problem of the collapse of the roof of the Bailuyuan tunnel during construction, the causes of collapse were analyzed, targeted treatment measures were proposed, and the effects of the treatment measures were evaluated through on-site monitoring and three-dimensional numerical simulations. The results showed that the particular characteristics of loess and the synergy of groundwater were the internal causes of the tunnel’s collapse as well as, to a certain extent, atmospheric precipitation. Therefore, the combination of multiple factors contributed to the tunnel’s collapse. Untimely monitoring and measurement, as well as the low initial support parameters, reflect a lack of human understanding of the collapse. Based on the analysis of the causes of the collapse, comprehensive treatment measures for inside and outside the tunnel are proposed, which are shown to be effective and to be capable of preventing the occurrence of further collapses. After the collapse treatment, the measured maximum settlement of the tunnel vault was 65.1 mm, the maximum horizontal convergence was 25 mm, the maximum surrounding rock pressure was 0.56 MPa, and the maximum stress on the steel arch frame was 54.34 MPa. Compared with the original design plan, the vertical stress, horizontal stress, and shear stress of the surrounding rock obtained from numerical simulation after the collapse treatment were greatly reduced, the reduction rate at the vault reached 50%, and the safety factors of the initial support positions after treatment met the specification requirements. The research results can provide engineering guidance for the design and construction of large-section tunnels crossing deep-loess strata, and they are of important engineering significance.

The characteristics of the aerodynamic effects of high-speed trains passing in a shield tunnel were studied using the three-dimensional, compressible, unsteady Reynolds-averaged Navier-Stokes (RANS) equations for the simulation analysis. Numerical calculations were compared with dynamic model tests to verify the reliability of the numerical simulations. The results showed that the compression wave characteristics of high-speed trains in shield tunnels were consistent with those in molded concrete tunnels. When high-speed trains met in the middle of the shield tunnel, the positive and negative peak attenuation rates of shield tunnels were higher than the positive and negative peak attenuation rates of molded lining tunnels, and the maximum pressure attenuation rate could reach 57.8%. At the same time, the micro-pressure wave of the former was reduced by 10.78%, compared with those of the latter. When meeting cars at different locations, the maximum pressure at the intersection in the center of the tunnel was significantly higher than those at other intersection points in the tunnel. Different intersection positions and different tunnel lining structures had relatively little influence on the aerodynamic drag and lateral force, while train speed had a significant influence.

Due to the long-term coupling effect of a train load and groundwater, the surrounding rock at the tunnel bottom will soften in a certain range and the mechanical parameters of the surrounding rock will decrease, causing the uneven distribution of the confining pressure at the tunnel bottom and affecting the base concrete structure service life. In this research, the method of combining field tests and numerical simulation is adopted, and the vertical displacement, vertical acceleration, and maximum and minimum principal stresses are used as evaluation indicators. The dynamic response law of the base structure with the softened surrounding rock of the heavy-duty train is analyzed, and the Miner linear cumulative damage theory is introduced to obtain the service life of the tunnel bottom structure under different softening conditions. The results show that with the decrease in the softening coefficient and the increase in the softening thickness of the bedrock, the displacement, acceleration, and principal stress response indexes of the structure increase by varying degrees, and the service life of the base structure decreases almost linearly. The maximum vertical displacement, acceleration, and tensile stress are located directly below the track, and the maximum compressive stress is located at the connection between the inverted arch and the side wall. According to the predicted value of the service life, the reliability of the base structure is divided into four levels: safety, warning, danger, and serious danger.

This paper discusses research on the dynamic response characteristics of a heavy-haul railway tunnel and the surrounding soil under the conditions of substrate health and a base void. The detection results of the base condition of 20 double-track tunnels for a heavy-haul railway show the main distribution law of base voids. Based on this, a 1:20 scale test model of a heavy-haul railway tunnel is established. The vibration load of the train is established by a vibration exciter arranged at the tunnel invert. The dynamic response and attenuation law of a heavy-haul railway tunnel lining structure and the surrounding soil are tested using acceleration sensors, strain gauges, and soil pressure boxes. The research results show that most of the diseases are concentrated below the heavy-haul line. The base void causes the peak acceleration of the nearby tunnel invert to increase by 55.6%. Tunnel annular construction joints reduce the conductivity of the vibration waves in the axial direction of the tunnel. The acceleration attenuation rate of the soil above the tunnel invert is significantly less than that under the invert. The base void reduces the acceleration of the nearby soil layer by 19.4% and increases the stress on the surface of the nearby tunnel invert by 21.3%, and the stress change amplitude increases by 0.55%. The tunnel structure in the area of the base void experiences fatigue damage. The base void causes the compaction and bearing capacity of the nearby soil to decrease and the softening speed of the tunnel basement soil layer to increase. Therefore, for the basement damage to heavy-haul railway tunnels, “early detection, early treatment” should be performed.

This study investigates the dynamic response characteristics of the tunnel bottom structure, focusing on a heavy-haul railway tunnel. To assess the condition of the tunnel bottom, geological radar and drilling core techniques were employed, along with on-site dynamic testing. The dynamic stress and acceleration response characteristics of the tunnel bottom structure, situated in grade V surrounding rock, were analyzed under axle loads of 25 t, 27 t, and 30 t. Both time-domain and frequency-domain analyses were conducted to explore the impact of structural defects on the dynamic response of the tunnel bottom. The results indicate that the dynamic response of the tunnel bottom structure increases linearly with increasing train axle load. In the presence of void-related defects at the tunnel bottom, the dynamic response of the structure is amplified, with an observed growth rate of up to 26.3%. Furthermore, the load exerted by heavy-duty trains on the tunnel bottom structure is predominantly a low-frequency effect, concentrated within the range of 0–20 Hz. Analysis of the 1/3 octave band reveals that the maximum difference in acceleration levels occurs at a center frequency of 31.5 Hz. Additionally, as the distance between the measurement point and the vibration source increases, the dynamic response induced by the void defect on the tunnel bottom structure weakens.