| As a controllable project for mountain highway construction,the tunnel has been widely used in China's plateau mountains and low-lying hills.However,the construction of the tunnel enhances the capacity of the mountain roads,but it will also inevitably bring about a series of environmental problems,such as regional water loss,water quality deterioration,air pollution,tunnel slag and soil erosion intensity,etc.The daily production and life of residents near the district has had a serious negative impact.To this end,this paper takes the G318 Linzhi-Lhasa section highway reconstruction project Mira Mountain high-altitude environment sensitive area special tunnel as the research object,the water environment,atmospheric environment,solid waste environment and ecological environment in the tunnel area are simulated and evaluated using the system dynamics?SD?method to build a green ecological high-altitude road tunnel with little environmental negative effects and well social recognition.Based on the systematic discourse of the environmental effects during the construction and operation of highway tunnels,this paper combines the results of theoretical analysis,public participation and on-site investigation to select the water environment,atmospheric environment,solid waste environment and ecological environment as the evaluation factors and system dynamics as the evaluation method.Considering the dynamic delay and high-order nonlinearity of environment in high altitude areas,high-altitude tunnel environment impact SD evaluation model is constructed in this paper.A causal relationship diagram including 30 environmental factors is established,and then the properties of different variables are further distinguished.A stock flow diagram with 6 level variables,12 rate variables,26auxiliary variables and 62 parameters is constructed.The improved interval number analytic model based on the decision-makers'preference information is used to determine the environmental investment proportion of each environmental element in the tunnel area:water environment 0.3509,atmospheric environment 0.2779,solid waste environment 0.1302,ecological environment 0.2410.Xueshanliang Tunnel and Yankoushan Tunnel are selected to verify the reliability of the SD model,which is used for the environmental impact simulation assessment of Mira Mountain Tunnel.Conclusions are obtained below:?1?The water loss in the tunnel construction area has continued to increase during the construction period.The regional water loss from 2015 to 2016 has slowly increased from 0 to 1 million m3,and from 2017 to 2018,it has rapidly increased to 4 million m3;During the operation period,the amount of water resources rebound slightly,but the change is not obvious.The SS content of the water body increases linearly during the construction period,reaching a peak of 106 tons in July 2018.After 2019,due to the change of the system leading feedback,the SS content of the water body gradually decreased,reaching 30 tons by 2032 of a reasonable range.?2?TSP emissions continue to increase during the construction and operation and are concentrated outside the tunnel.From 2015 to 2018,TSP emissions increased from0 to 750 tons,and reached 1,000 tons by 2032.NO2 emissions are mainly concentrated after tunnel operation,small cars are the main source of NO2.During the entire construction phase,only 4.2 tons of NO2 are discharged.and the total emissions by 2032is close to 1,200 tons.However,compared with the local atmospheric environment capacity,the emissions of TSP and NO2 are under the allowable range.?3?The solid waste discharge of Mira Mountain Tunnel is on the rise during the construction period,especially after 2017,the growth rate has increased significantly,reaching a peak of 2.33 million tons in July 2018;it has slowly declined to 227 million tons during the operation period.?4?During the tunnel construction period,the amount of new soil erosion increased linearly,reaching a peak of 1,300 tons in July 2018,and the waste slag yard is the most serious unit of soil erosion in the whole region.which is effectively controlled after operation.The new quantity in 2032 is less than 1,000 tons,which is much lower than the allowable soil loss in the tunnel.Results show that construction of Mira Mountain Tunnel has the greatest impact on solid waste during the construction and operation period,followed by water and atmosphere,and the disturbance to the local ecological environment is little,which is in line with the environmental protection planning of Tibet.Based on this,reasonable solid waste treatment measures are proposed to realize the coordination and unification of the construction of Mira Mountain Tunnel and environment protection,which can provide a useful reference for the environmental impact assessment of tunnel construction in similar areas. |
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