| At present in the design phase of ventilation system of road & railway tunnel, generally rule of thumb to determine the natural wind speed value inside the tunnel, normally based on the specification. With the increase of extra-long tunnel construction, obviously, the empirical value can not keep up with the actual. So it needs to work out a method for natural wind computation. In this thesis, natural wind in deeply buried extra-long highway tunnel has been studied based on the project of 10 km long Niba Mountain extra-long highway tunnel. Studies to be undertaken are as follows:Firstly, with the univariate analysis on the effects of internal and external influence factors, the influencing mechanism of each key factor has been got. In addition, the theoretical formula for natural air flow caused by the excess differential static pressure or thermal potential difference has been derived. The natural air flow under the action of each key factor is calculated by numerical simulation and programming, the two results agree well. This verifies the theoretical formulas are reasonable.Secondly, the field test of three typical road tunnels-the Erlang Mountain Tunnel, Tiefeng Mountain No.2 Tunnel and the Fangdou Mountain Tunnel have been carried out. The analyzing result of the field test shows that atmosphere pressure and temperature should be the leading external environmental factors influencing the natural wind in deeply buried extra-long tunnels, while the influence of humidity is minor. Method of determining natural wind in each section has been established for the deeply buried extra-long tunnels of ventilation shafts by study, which is combining the measured meteorological data at the tunnel portals with 3D numerical computation model. The calculation results show that the numerical results of the three tunnels consistent with the measured wind speed. This provides a strong guarantee for studying natural wind in each section of Niba Mountain Tunnel.Then, with the establishment of automatic weather stations as well as the long-term meteorological observation and monitoring of the two main tunnel adits and two shaft exits of Niba Mountain Tunnel, the natural wind speed of each section has been worked out by the method researched previously. Considering numerical calculation spends more time, within the error range allowable in the applications, combining the specific parameters of tunnel with theoretical formulas derived to make a routine calculation according to previous experience, thus it improves the efficiency of calculation and analysis.Finally, natural wind speed frequency distribution and the extreme wind speed in each section have been got by statistically processing of the routine calculation results.Similarly, the method of calculation natural wind for long road tunnel is also applicable to long railway tunnel. Natural wind in the caves ofâ… line &â…¡line tunnel were programming calculated on the basis of the meteorological data collected from weather stations of Guanjiao Railway Tunnel. The calculations are divided into two cases-closed shaft and open shaft.As known from the calculation, the natural wind speed of each section in both Niba Mountain Tunnel and Guanjiao Tunnel vary widely. The research results can make up the shortcomings of specification by using empirical speed value to simulate the natural wind in tunnel. It can be used as references for ventilation system design of both tunnels. |
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