Cracks in the lining significantly reduce the safety of a tunnel during operation. It is urgent to figure out the influence of cracks on tunnel carrying capacity. In this paper, three-dimensional model tests were conducted to investigate deformation, internal force, and deterioration laws of the lining with prefabricated cracks at different positions. The main conclusions were obtained as follows: (1) The carrying capacity of the lining structure with prefabricated cracks was reduced, and the deformation of the lining structure increased. The penetration of the vault crown crack accelerated the damage of the lining structure, and structural failure occurred when the crack went through at the left arch spring. (2) The internal force of the lining was greatly affected by the positions of prefabricated cracks. The internal forces of the lining structure decreased with the existence of prefabricated cracks. Whether or not there were prefabricated cracks, tension cracks appeared in the inside fiber of the vault and inverted arch. (3) The deformation of the lining structure with the existence of prefabricated cracks increased. When the prefabricated crack was located at the vault, the deformation was the largest, followed by the arch spring, side wall, and arch shoulder. (4) The analysis shows that prefabricated cracks at the vault are the most damaging under stress and deformation of the lining structure, so longitudinal cracks at the vault should be strengthened.

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 study uses ordinary Portland–sulfate–silicate composite cement as the matrix and investigates the effects of water–cement ratio, HPMC dosage, and PCS dosage on the performance of specialized grouting materials for subway structure repair during operation through single-factor experiments and orthogonal experiments. Multifactorial variance analysis was employed to quantitatively evaluate the sensitivity of each factor and their interactions to slurry flowability, setting time, anti-dispersibility, and compressive strength. The results show that the water–cement ratio is the most critical factor affecting the performance of the grouting material, with extremely significant impacts on all performance indicators; HPMC dosage significantly affects flowability, setting time, and anti-dispersibility; PCS dosage primarily influences 2 h compressive strength; the interaction between water–cement ratio and HPMC dosage has a significant impact on anti-dispersibility. Principal component analysis revealed the trade-off relationship between flowability, setting time, and strength. The study established a sensitivity ranking for the performance of specialized grouting materials: water–cement ratio > HPMC dosage > PCS dosage > interaction, providing a theoretical basis and methodological reference for the formulation optimization of specialized grouting materials for subway structure repair during operation.

Although the rapid expansion of urban rail transit offers convenience to citizens, the issue of subway vibration cannot be overlooked. This study investigates the spatial distribution characteristics of vibration in the Fayuan Temple historic and cultural reserve. It involves using a V001 magnetoelectric acceleration sensor capable of monitoring low amplitudes with a sensitivity of 0.298 V/(m/s²), a measuring range of up to 20 m/s², and a frequency range span from 0.5 to 100 Hz for in situ testing, analyzing the law of vibration propagation in this area, evaluating the impact on buildings, and determining the vibration reduction scheme. The reserve is divided into three zones based on the vertical vibration level measured during the in situ test as follows: severely excessive, generally excessive, and non-excessive vibration. Furthermore, the research develops a dynamic coupling model of vehicle–track–tunnel–stratum–structure to verify the damping effect of the wire spring floating plate track and periodic pile row. It compares the characteristics of three vibration reduction schemes, namely, internal vibration reduction reconstruction, periodic pile row, and anti-vibration reinforcement or reconstruction of buildings, proposing a comprehensive solution. Considering the construction conditions, difficulty, cost, and other factors, a periodic pile row is recommended as the primary treatment measure. If necessary, anti-vibration reinforcement or reconstruction of buildings can serve as supplemental measures.

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.