ABSTRACT
Failures commonly occur in high angle approach cuts and initial subsurface of tunnel portal. Because the portal comprises an interface between the surfaces and subsurface, both rock slope and tunnel engineering approaches are needed for portal design. Also, specific information in portal related failures do not exist and traditional design methods are inadequate for utilization in complex three dimensional area. In this paper, portal of a tunnel is simulated by FDM method. Among many factors which are affected the portal stability, trench angle, cohesion and friction angle has been studied. The friction angle in the main model is 36 degree and cohesion is 8 MPa. Also, trench angle has decreased and increased 15 degree, cohesion and friction angle increased and decreased 15 percent and their effect on portal stability and displacement studied separately. Finally, based on tunnel span and plastic zones, 2D and 3D stress-strain field has distinguished.
