The orientation of geological discontinuities, such as joints and faults, relative to the tunnel axis significantly influences the stability of an underground excavation. Geological discontinuities are planes of weakness in the rock mass that can affect its strength and deformation characteristics. Joints are fractures in the rock along which there has been little or no displacement, while faults are fractures along which there has been significant displacement. The angle between the discontinuity and the tunnel axis, as well as the dip angle of the discontinuity, are key factors. When discontinuities are oriented parallel or sub-parallel to the tunnel axis, they can create long, continuous planes of weakness along the tunnel walls or roof. This can lead to instability, particularly if the discontinuities are poorly interlocked or filled with weak material. For example, if a tunnel is excavated parallel to a major ....
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