The Evolutionary Effect Of The Ecological Environment Along The Surge Flow Path Of A Typical Mountain Railroad Tunnel

As a common large-scale subsidiary project in mountain railroad construction,tunnels play a significant role in improving railroad routes and railroad traffic efficiency,driving the rapid development of Chinese railroads.However,while creating considerable economic and social benefits,the complexity of the construction environment and the restrictive nature of the technical operation of mountain railroad tunnels determine that they will inevitably cause disturbance and damage to the adjacent ecological environment during the construction process.The direct or indirect negative impact on the ecological environment caused by the tunnel water surges is extremely serious.Therefore,it is of great significance to study the quality changes of the ecological environment along the water inflow path and the related influencing factors of water inflow in the whole life cycle,which is important for clarifying the mechanism of the ecological environment changes along the surging water of the mountain railroad tunnel,providing scientific decision support for the environmental planning of the mountain railroad tunnel,and realizing the coordinated development of both tunnel construction and environmental protection.This study is based on the remote sensing image data of the area where the case mountain railroad tunnel is located from 2005 to 2020.After comparing the buffer areas at multiple scales,this paper selects the buffer area range of 1000 m along the case tunnel surge flow path as the study area.From the perspective of the whole life cycle of tunnel construction,based on the remote sensing ecological index and change vector analysis method,this paper analyzes the spatial and temporal distribution characteristics of ecological environment quality in the study area,and reveals the spatial and temporal evolution law of the ecological environment along the case tunnel surge path during the whole life cycle.At the same time,this paper constructs the ecological environment quality driving force index system from natural and anthropogenic aspects,and analyzes the changes of ecological environment influencing factors in the study area by using geographic detectors,and provides feasible suggestions according to the analysis results.The main results derived from this paper are as follows.（1）The remote sensing ecological index（RSEI）of the buffer zone along the case tunnel surge water runoff is mostly in the range of 0.25-0.75.Before the construction of the tunnel,there was a significant "single-peak" distribution.During the construction period,the distribution was "double-peaked".After the construction period,the distribution becomes "single-peaked".The RSEI varies significantly before and after construction.In terms of spatial distribution,the ecological environment in the areas near the tunnel exit,on both sides of the railway line and the inflow path after construction is significantly worsened.The spatial clustering of RSEI cold spots and hot spots in the study area during the whole life cycle are significantly enhanced.The area percentage of RSEI level change from largest to smallest is: slightly decrease > basic stability > slightly increase > significantly decrease > significantly increase.During the construction period,the greatest variation of RSEI was observed in the range of 250-550 m from the tunnel exit.After the construction build-up,the greatest variation of RSEI was observed in the range of 300-450 m and 750-850 m from the tunnel exit.Overall,it shows the lowest average RSEI distributed in the center area of the tunnel exit and gradually increases along the interval gradient.（2）Among the influencing factors related to the ecological environment quality and water inflow in the buffer area along the water inflow path of the case tunnel,the strength of each influencing factor on the RSEI before construction is built is between 0.11 and0.2.The change of ecological environment in the study area is mainly influenced by natural elements such as elevation,distance to water system and anthropogenic elements such as distance to administrative area.During the construction period,the intensity of the effect of each influence factor is between 0.01 and 0.03.The influence of single factors such as slope and elevation on RSEI gradually diminishes.The combined effect of surge water and other construction factors and the influence factors within the driving force index system on the ecological environment of the study area gradually strengthens.After construction,the intensity of the effect of each influence factor is between 0.05 and 0.10.The influence of elements related to urban development such as distance to the highway and distance to the administrative district on the ecological environment of the study area after construction gradually strengthens.