Research On Slope Stability Around Tunnel Entrance In Loess Areas

Most of the Yanzhen-Tongguan section of Zhen-Xi passenger railway line traverses the loess areaes. This thesis is aimed to analyse and evalulate the stability of the natural slope before the construction of the railway line and the cutting slope and the face upward slope of tunnel portal after the construction of the railway line.The author participated in the preliminary prospecting of the Yanzhen-Tongguan section of Zhen-Xi passenger railway line, so the distributions and failure modes of the natural loess slope in the areas are classified, on the basis of field survey. Because many factors will influence the stability of the natrural loess slope, in order to evaluate the main factors, the grey correlation analysis theory is used to evaluate the factors. According to the theory, the stability of the slope before the construction of tunnel is estimated, by the comparison the correaltion of the unknown slope and the known slope. As the result shows, the stability of slope can be estimated quickly and exactly, using the grey correlation analysis method. A program is offered by the author, in order to estimate the stability of slope more exactly and easily.Based on the strength reduction method of FEM, by comparing the stability coefficient of slope, the stability of cutting slope and the slope under different locations of tunnel portal, are analysed and evaluated after the construction of tunnel portal. Furthermore, according to the different influence to the slope, the most rational location of tunnel portal on the slope is confirmed.The research shows that:(1) For the first typical slope (the slope of the inlet part of Fucun No.l Tunnel), the tunnel portal should be built at 8-10 m from the slope foot, and the face upward slope ratio should be 1:0.75.(2) For the second typical slope (the slope of the exit part of Panxi Tunnel), the tunnel portal should be built at 20-22 m from the slope foot, and the face upward slope ratio should be 1:1.25.