1. Part 8 MAPPING DISCONTINUITIES UNDERGROUND

2. Unlined tunnel excavations offer an unimpeded three- dimensional view of the rock fabric and structure. The floor (invert) of a tunnel is not commonly mapped because it is usually covered with tunnel muck, debris, and water. This shows a road header working on the East Minneapolis sewer interceptor tunnel.Unlined tunnel excavations offer an unimpeded three- dimensional view of the rock fabric and structure. The floor (invert) of a tunnel is not commonly mapped because it is usually covered with tunnel muck, debris, and water. This shows a road header working on the East Minneapolis sewer interceptor tunnel.

3. Common tunnel block failure modes caused by the intersection of the tunnel opening with crossing joints

4. The discontinuities intersecting any underground opening need to be recorded and described, as best possible form exposures within and exterior to the opening.The discontinuities intersecting any underground opening need to be recorded and described, as best possible form exposures within and exterior to the opening. When working near the ground surface it is advantageous to employ impression packers to examine fractures out-of-view, but in close proximity to the opening, as shown at left (arrow).When working near the ground surface it is advantageous to employ impression packers to examine fractures out-of-view, but in close proximity to the opening, as shown at left (arrow). Impression packers used

5. Fracture Maps Fracture maps are 2D representations of 3D underground openingsFracture maps are 2D representations of 3D underground openings Record the geometry and physical characteristics of individual fractures and geologic contactsRecord the geometry and physical characteristics of individual fractures and geologic contacts

6. Typical fracture mapping within a circular tunnel excavation. Note survey stationing and absence of information collected from the tunnel invert.Typical fracture mapping within a circular tunnel excavation. Note survey stationing and absence of information collected from the tunnel invert.