Numerical investigation on the smoke behaviour and longitudinal temperature decay in tilted tunnel fire with portal sealing

Blocking the tunnel portal is one strategy in railway tunnel firefighting. In order to evaluate the effect of tunnel portal sealing ratio on fire behaviour, Fire Dynamics Simulator (FDS) was used to simulate tilted tunnel fire with different slope angles varying from 0% to 5%, heat release rate varying from 10 to 50 MW and sealing ratios varying from 0% to 75%. Results show that the experimental data of the temperature distribution inside the tilted tunnel were in good agreement with the simulation results. Moreover, the ceiling temperature rise decreases along the tunnel with the increase of the tunnel portal sealing ratio at initial stage and then tends to stabilize because of less oxygen supply when the heat release rate is relatively large. The maximum temperature rise decays exponentially along the tunnel ceiling with distance. The current model for temperature decay beneath the tunnel ceiling was proposed to be modified by taking the tunnel entrance sealing ratio into account. The predictions by the modified model agree well with the experimental measurement. The results could provide practical information and knowledge in ventilation system design and emergency evacuation for inclined railway tunnels.

Research on Light-Dark Adaptation of Human Vision in Tunnel Portals

To study the characteristics of light and dark adaptation in tunnel portal sections and to determine the influencing factors of light-dark vision adaptation, basic tunnel lighting and linear design data are obtained. In this paper, we use a light-shielded tent to simulate the dark environment of a tunnel in experiments, observe the driver recognition time of target objects during the light-dark adaptation process, and analyze the light-dark adaptation time of human vision. Based on a large number of experimental data, we examined the relationship between age, gender, illuminance and light and dark adaptation times and established a model of the relationship between age, illuminance and light and dark adaptation times. The experimental results revealed that the dark adaptation time is generally longer than the light adaptation time. The dark adaptation time is positively related to age and basically exhibits a cubic relationship. There is no significant correlation between the light adaptation time and age, but the overall trend is that the light adaptation time gradually increases with increasing age. There is no correlation between gender and light and dark adaptation times, but there is a notable correlation between the light and dark adaptation times and illuminance. When the illuminance ranges from 11000-13000 lux, the light and dark adaptation times are the longest.

Structure Strengthening Method for Enhancing Seismic Behavior of Soft Tunnel Portal Section

Tunnel portal sections always suffer serious damage under strong earthquakes. This paper aims to study the seismic performance of lining strengthening method in soft rock portal section by employing the model test. Firstly, the shaking table test considering the test cases, the modified input motions, the boundary condition, and monitoring equipment are conducted to simulate the seismic response of the soft tunnel portal section. Then, the lining strengthening method of increasing concrete grade is applied to the tunnel structure to study the aseismic performance of the soft rock tunnel portal section, and the seismic effects of the tunnel linings with different concrete grades are compared and analyzed. The result shows that the proportion of soft rock to total surrounding rock is the key factor affecting the seismic response of soft rock tunnel portal section; the larger the proportion of soft rock in surrounding rock, the more vulnerable the structure to earthquake damage; the seismic performance of the lining strengthening in hard rock portal is remarkable while limited in soft rock portal section. The stiffness and strength of the lining are larger than those of surrounding rock; the seismic performance of the soft portal section could hardly be improved only by the lining strengthening method. It is suggested to adopt both the structure strengthening and isolation method in the seismic design of soft portal section.

Discussion on Landscape and Greening Technology of Highway Structural Tunnel Entrance

Highway tunnel entrance is not only the exposed part of mountain in the tunnel engineering, but also an integral part of the highway breaking through the mountain. On the premise of ensuring the safety of tunnel entrance, it is important to realize the unity of safety and practical “stability” and landscape greening “beauty” of the expressway tunnel through reasonable aesthetic landscape greening design. In combination with the topographic and geomorphological conditions as well as the regional and humanistic conditions of the highway tunnel portal area, this paper introduces the cultural landscape and plant greening engineering of highway tunnel entrance by reference to the successful experience of tunnel entrance landscape greening, and puts forward the requirements for landscape and greening technology of highway tunnel entrance in accordance with the provisions of relevant regulations.

Slope stability analysis of the drainage tunnel portal in Tanju Dam, Dompu District, West Nusa Tenggara

This paper presents design results of the tunnel portal slopes at the Tanju Dam, Dompu, West Nusa Tenggara. The objective of this research was to analyse the stability of the tunnel portal slopes using circular failure chart (CFC) method, limit equilibrium method (LEM), and finite element method (FEM). Input parameters were obtained from drill core evaluations and laboratory tests. By considering the rock mass rating (RMR) values of rock masses, which are categorized as class II, at the two slopes, adjustments for the cohesion and inner friction angle values are made. The inlet slope (IL) have cohesion values of 350 kPa and 40º inner friction angle and the outlet slope (OL) have cohesion values of 400 kPa and 45º inner friction angle. The CFC method shows that the IL and OL have safety factor (FS) values of 3.5 and 3.44, respectively. The LEM shows that the IL and OL have the FS values of 3.69 and 3.65, respectively. Meanwhile, the FEM shows that the IL and OL have FS values of 4.78 and 4.79, respectively. The stability analysis results indicate that designed slopes are stable.