Yinjun Tan

High-temperature smoke generated by tunnel fires is the most important factor causing casualties. To explore the influence of natural wind on fire smoke movement in an extra-long highway tunnel based on the Taihang Mountain Tunnel, the distribution law of natural wind in the tunnel was obtained by on-site monitoring of the meteorological conditions at the tunnel site. A three-dimensional fire dynamics tunnel model considering an inclined shaft smoke exhaust was established, and the influence of natural wind on tunnel temperature distribution, smoke spread and smoke exhaust efficiency was studied. The results show that the natural wind speed of the Taihang Mountain Tunnel is mainly concentrated at 0~3 m/s. The main wind direction of the natural wind on the left tunnel is opposite to the driving direction, and the distribution probability of the main wind direction in each section is 81.27% and 72.15%, respectively. The main wind direction of the right tunnel is the same as the driving direction, and the distribution probability of the main wind direction in each section is 56.78%, 69.73%, 67.32% and 64.65%, respectively. The negative natural wind can inhibit the smoke spread downstream of the smoke exhaust port, but it is not conducive to the smoke exhaust. The positive natural wind promotes the smoke spread to the downstream of the smoke exhaust port, and the larger the natural wind speed, the longer the spread length. Natural wind reduces the smoke exhaust efficiency. For positive or negative natural wind with a guaranteed rate of 70%, the smoke exhaust efficiency is reduced by 27.76% and 15.59%, respectively, compared with the condition without natural wind. The research results can provide a useful reference for the design of fire smoke exhausts and smoke control schemes in extra-long highway tunnels.

The deformation characteristics and the timing for secondary lining support in high geo-stress soft rock tunnels have drawn significant attention. In carbonaceous shale formations, tunnel construction deformations are very pronounced under construction disturbances due to the development of joints, dense fractures, and poor interlayer bonding. With the Xishuangbanna tunnel as our research backdrop, this study meticulously analyzed the deformation patterns and characteristics inherent to high geo-stress tunnels constructed within carbonaceous schist formations. Employing a comprehensive approach involving full displacement analysis and on-site construction mechanics testing, we utilized the displacement release rate and structural safety factors as key indicators to determine the secondary lining supporting time. Employing this innovative approach, we successfully identified the ideal junctures for implementing secondary lining support in tunnels excavated through high geo-stress carbonaceous schist. The research findings indicate that the primary damage modes in high geo-stress carbonaceous schist tunnels are initial support failure and extensive early support deformation. These vulnerabilities are primarily attributed to weak and fragmented strata, elevated ground stress levels, and inadequate support strength. During the early stages of tunnel construction, substantial deformations are observed, exhibiting high rates of change. Horizontal convergence, notably, significantly surpasses the settlement at the tunnel’s crown. When employing the three-bench method for construction, the deformation occurring before the excavation of the middle bench contributes the most to the total deformation monitored, whereas the deformation generated after the excavation of the inverted arch constitutes a minor proportion. The tunnel’s crown and invert experience tension while the secondary lining undergoes compression. The internal forces are most significant at the tunnel’s hance and knee, with the left tunnel knee being the weakest section of the secondary lining. The findings of our study are poised to guide the design and execution of tunnels constructed within high geo-stress carbonaceous schist formations.

The gently tilt-layered shale displays anisotropic behavior and includes structural planes that cause the rock to exhibit weakened features. As a result, the load-bearing capacity and failure mechanisms of this type of rock differ significantly from those of other rock types. A series of uniaxial compression tests were performed on shale samples from the Chaoyang Tunnel to investigate damage evolution patterns and typical failure characteristics of gently tilt-layered shale. An acoustic emission testing system was incorporated to analyze the acoustic emission parameters of the shale samples during the loading process. The results indicate that the failure modes of the gently tilt-layered shale are significantly correlated with the structural plane angles and water content. The shale samples gradually transition from tension failure to tension-shear compound failure as the structural plane angles and water content increase, with an increasing level of damage. The maximum values of AE ringing counts and AE energy for shale samples with diverse structural plane angles and water content are reached near the peak stress and serve as precursors to rock failure. The primary factor influencing the failure modes of the rock samples is the structural plane angle. The precise correspondence between the structural plane angle, water content, crack propagation patterns, and failure modes of gently tilted layered shale can be captured by the distribution of the RA-AF values.