| Sichuan-Tibet Railway is an important part of the national rapid railroad network,and promoting the construction of Sichuan-Tibet Railway can open up the artery of transportation between Sichuan and Tibet area.However,there are many nature reserves and scenic spots locating along the line of Sichuan-Tibet railway.The ecological environment is complicating,sensitive and fragile.The elevation fluctuates greatly and the geological activities are active.To reduce or avoid the ecological destroy along the lines caused by the extra-long tunnel construction of Sichuan-Tibet railway,it should be evaluate the ecological influence of the project and select the proper ecological protection measures on the basis of the evaluation.So it is necessary to establish the general evaluation of the ultra-long tunnel ecological influence by combing the regional and project traits of Sichuan-Tibet railway.Considering the features of Sichuan-Tibet railway ultra-long tunnel such as long period,large scale and the wide distribution of the rare animals and plants,the paper analyzes the environmental influences of all stages of the project,improves the gray theory by the combination weighting model,establishes the comprehensive evaluation model of the ecological influence and finally tests the feasibility of the model by the four parts of the tunnel in Lalin.First,the paper briefly analyzes the connections between the ecology and environment and the ultra-long tunnel project in the stages of surveying,designing,constructing and operating,selects the adverse effect factors to the surrounding ecological environments caused by the ultra-long tunnel and establishes the 11 criterion level indexes and 27 scheme level comprehensive evaluation indexes.Second,the paper selects the index weighting model and the comprehensive evaluation model.Because of the various evaluation indexes,complex levels and the ambiguity,the paper amends the G2 by the entropy evaluation method,to establish the combination weighting model and weight kinds of the indexes.Considering the features of dynamic retard trait,hierarchy and higher-order non-linearity,improving the gray target model by G2 amended by the entropy method to establish the ecological effect comprehensive evaluation model based on the gray target theory.The target degree and index contribution can be counted by the comprehensive evaluation model.Target degree is to reflect the influence to the surrounding ecological environment by the ultra long tunnel and the index contribution can reflect the index influencing the environment in the larger scale.At last,the paper selects the four parts of Lalin named Dagala tunnel,Gongduoding tunnel,Gangmulashan tunnel and Milin tunnel to text and calculates the target degrees of the four tunnel are 0.800,0.804,0.790 and 0.744 respectively.Besides the light influence of Gongduoding tunnel,the other three tunnels can influence the ecological environment in the medium degree.At the same time,the main indexes to influence the ecology are forest coverage,decline rate of top vegetation,content of petrochemical pollutants,landscape optical distance,ground water loss rate and nitrogen dioxide content according to the contribution degree of 27 indexes.The two matches basically by contrasting the evaluation result and the reality.It proves that the evaluation index systems and the comprehensive model can be feasible to work out the real problems.It can enrich and improve the ecological effect evaluation index of the ultra long tunnel and provide the reference to the sustained development of civil engineering with the value of application. |
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