In mountainous areas natural slopes are adapted for construction of roads and other infrastructure, and slope instability is the major problem arising from artificial slopes. Investigating the endangered areas and potential slope failure mechanisms is essential to ensure stability. In this paper, stability analyses of a 75-year-old masonry-lined Turkish State Railway Tunnel and the stratified rock slope above the tunnel following the road cut excavation are presented. Finite Element Method is used to evaluate the stability of this structurally coupled system. The tunnel is located next to Zonguldak-Amasra-Kurucasile highway which is under construction at present.


On the transition section of Zonguldak-Amasra-Kurucasile highway route between Km 26 + 590 and Km 26 + 700, a road cut will be excavated by bench blasting to obtain a road cut slope consisting of different number of benches at various cross sections. Slope excavation will be made on a rock mass that is above No 50 Turkish State Railway Tunnel. This shallow railway tunnel has been in service for more than 75 years, and it is stable. Figure 1 shows tunnel portal, nearest residential area and natural terrain around the tunnel. Figure 2 shows masonry lining and inner view of the railway tunnel.

When the road-cut slope is excavated, some of the rockmass will be removed and a stress relief is likely to occur in the rock mass surrounding the tunnel. In a typical section accepted as critical, some of the benches are planned to be as close as around 66 m horizontally to the tunnel sidewall. Overburden amount is expected to be around 55 m above the upper boundary of the railway tunnel at that critical section. Another critical factor is the distance of tunnel and planned slope cut section to the nearest apartment building at Denizkent Condominium Site. The distance between the apartments and intersection point of a line drawn from the tunnel roof to the surface is around 88 m horizontally (Fig. 3).

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