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The steel rib and the lattice girder are two typical steel arch frames used in the primary lining of the New Austrian Tunnelling Method (NATM) highway tunnel. In the process of tunnel construction, it is necessary to choose the support method according to the mechanical properties, durability, construction difficulty, and economic benefits. In order to analyze the mechanical characteristics of steel arch frames, a loading and measurement test system for steel arch was designed, and destructive tests were carried out on a three-bar lattice girder, four-bar lattice girder, and I-beam steel rib. The steel utilization coefficient was introduced to compare the mechanical properties of the different types of steel frames. The results show that the I-beam steel rib has the largest steel utilization coefficient, but it is not well combined with concrete. Among the lattice girders, the three-bar W-shaped lattice girder uses the least amount of steel under the same load, which reduces the construction cost and is worth applying and popularizing. Additionally, the steel utilization coefficient of different types of lattice girders can be optimized through the ratio of steel bar diameters. It is proved that the steel utilization coefficient can provide a reference for the evaluation and selection of steel frames for the primary lining of highway tunnel engineering. [ABSTRACT FROM AUTHOR]

Fire is the most deadly risk during tunnel operation. Early rapid response and a reasonable smoke control plan are very important to evaluate tunnel fire performance. In order to study the relevant time factors for smoke management in a highway tunnel, firstly, the logical sequence and time of the fire alarm system (FAS) startup are investigated and analyzed. Then, according to the one-dimensional fluid mechanics model, the time rule of adjusting the airflow field in the tunnel from the normal operation stage to the emergency ventilation state is analyzed theoretically. Finally, the abovementioned theoretical formulas are verified through the employment of model experiments. The analysis shows that the time that passes from the start of the fire to when the exhaust fan is activated is close to 3 minutes. The time required to form a stable critical wind speed, however, is close to 7 minutes, which is longer than the 5 minutes it takes for the fire to reach its maximum temperature. Due to inertia, it takes about 0.5 to 2 minutes for the air velocity in tunnels of different lengths to drop from the traffic piston wind speed to the critical wind speed. If reverse smoke extraction is required, however, the duration is between 3 and 8 minutes. The conclusion is of guiding significance for the preparation of the emergency linkage control scheme for tunnels, as well as for the setting of initial boundary conditions for CFD fire simulations. [ABSTRACT FROM AUTHOR]

In order to prevent smoke from flowing backward and penetrating into adjacent tunnel through cross channels during evacuation in case of fire accidents in highway tunnels, it is extremely necessary to implement the linkage control scheme for double-hole tunnel ventilation system. Therefore, six linkage control schemes for ventilation system are proposed in this article. Firstly, these six schemes were numerically simulated through Fire Dynamics Simulator (FDS) to obtain the flow velocity, flow direction, and smoke distribution under different schemes when the peak power of fire accidents is 30 MW. And two better schemes were selected for further investigation based on the evacuation conditions in the upper stream of fire source. Secondly, a 1 : 10 scale model experiment was conducted to test these two schemes, and the results from numerical simulation and model experiment were compared and verified. Finally, the location of fire accident, the time to develop stable opposite airflow, and the number of open cross channels were analyzed to confirm the applicability of the recommended scheme. The results show that the optimal scheme is to switch on the fans in the upstream of the fire accident and the fans on both sides of the cross channel in the non-fire tunnel to form positive pressure to control the smoke flow. This scheme ensures a stable and uniform smoke flow in the cross channel and personnel's safety during evacuation. [ABSTRACT FROM AUTHOR]