Research Of Safety Assessment Method For Tunnel Entrance Section Based On GIS

The implementation of the Western Development Strategy has accelerated the development of China's western transportation network.The terrain in western China is mostly mountainous,and the proportion of tunnel construction in western traffic construction is very large.At the same time,in recent years,the slope of the tunnel entrance section is unstable and the collapse of the cave frequently occurs,resulting in low construction efficiency and great threat to workers' lives and property.Therefore,it is of great practical significance to study the safety evaluation method of tunnel entrance section by combining Geographic Information System(GIS)technology.In this paper,the geological three-dimensional model is used to realize the acquisition of the cover thickness and the display of the evaluation index.At the same time,the GIS method is used to visually express the influence degree of the evaluation factor on the tunnel entrance,which provides a reference for the safety evaluation of the tunnel entrance and establishes a safety risk assessment system.Taking the Meihuashan Tunnel as an example,the construction of the GIS-based tunnel entrance section safety evaluation system is realized.The specific research work and main conclusions are as follows:(1)According to the characteristics of on-site tunnel safety accidents,an evaluation index system consisting of four factors including the thickness of the cover,the surface of the slope,the distance from each point to the face,and the distance from each point to the central axis of the tunnel is constructed.(2)With the GRASS GIS platform,the surface elevation vector layer turns to the raster layer,and the terrain analysis layer in the software obtains the surface slope layer,and the buffer analysis obtains the distance from each point to the face and the layer of the distance between each point and the central axis of the tunnel.The thickness of the cover was predicted by regression Kriging,and the cover thickness layer was obtained by mask overlay of GRASS GIS.At the same time,a three-dimensional CDT(Constrained Delaunay Triangulation)geological model was established to obtain the display of the cover thickness and the final evaluation index.(3)The process of constructing the safety evaluation method based on GIS tunnel entrance segment: based on the research area data and digital elevation graph,the expert survey method and the analytic hierarchy process are used to determine the weight of four factors,and the risk evaluation level is established by the grade scoring system.Thus establishing a risk assessment method for the slope of the cave.In the GRASS GIS software,each factor is a layer,and the layers are superimposed to evaluate the security risk of the tunnel entrance segment.(4)The GIS-based tunnel entrance section safety evaluation system shows that the thickness of the cover layer plays an important role in the tunnel safety risk,and the surface slope is second.