The amount and sources of ground losses around the TBM are often measured using widely-spaced deep settlement points, extensometers, and inclinometers and surface settlements measured with settlement points. Uncontrolled runs or inflows of soils at the tunnel face may cause localized ground losses that progress upward as chimney-shaped voids and loosened soil zones. With ground loss and settlement monitoring points spaced 10 to 100 meters apart, it is unlikely that they will be positioned to effectively measure localized large excessive settlement zones that may be only a few meters wide.