| In the process of construction of long tunnels based on drill and blast method and trackless transportation,due to the spatial structure characteristics of "long cavern,multiple auxiliary contact channels" and the rapid construction needs of "multi-sectional cooperative tunnelling and internal combustion operation",the tunnel working space has a series of environmental problems such as large production,low efficiency of new air replacement and serious local concentration of harmful gases,and ventilation problems need to be solved.This study will rely on the Wushan extra-long tunnel in Chongqing section of the new ZhengzhouWanzhou high-speed railroad to carry out the study on the optimization of ventilation mode and the characteristics of spatial and temporal distribution of pollutants in extra-long railroad tunnel construction by combining theoretical analysis,field monitoring,numerical simulation and model test,and its research results mainly include the following aspects.(1)Through technical research,we mastered the physical and chemical characteristics of key pollutants during tunnel construction,clarified the permissible threshold values of key environmental parameters under the current industry specifications,and constructed a stagetype ventilation system under the drill-and-blast method of trackless transport mode for the construction characteristics of long tunnel chambers,multiple auxiliary channels,internal combustion operations,and coordinated operations of long railroad tunnels.(2)Through on-site monitoring and three-dimensional numerical calculation,the structural stability and longitudinal attenuation mechanism of wind flow field are analyzed,the spatial and temporal distribution characteristics of pollutants under blasting,grouting and drilling processes in extra-long railroad tunnels are investigated,the coupling effect of wind flow field and its mechanism of pressure difference are revealed,the obstructing effect of dollies on the diffusion of pollutants is explored,and the dynamic transport law of pollutants during the construction period under single-hole boring and double-hole collaborative boring of tunnels is obtained.(3)By means of theoretical analysis and model tests,the effects of dust particle size,initial dust volume,longitudinal return air rate,second lining step and other factors on key characteristics such as peak dust concentration,diffusion rate and dust reduction efficiency were studied,and the commonality of distribution and diffusion characteristics of nonhomogeneous dust particle population under different external physical field conditions was clarified.The research results of this thesis are not only applicable to the dependent project-Wushan tunnel project of Zhengwan high-speed railroad,but also have good significance for the design of ventilation system and control of pollutants during the construction period for similar extra-long double-line railroad tunnel construction through long inclined shaft into the main cavern section. |
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