When a drainage geotextile and a waterproofing membrane have to be applied to the primary lining intrados, an excessively undulating surface may cause the waterproofing membrane to stretch between crests and bridge over valleys. The fresh concrete poured against the membrane may excessively stretch the membrane, and then damage the membrane, which may then leak. The first figure illustrates the waviness criteria used at the Caldecott 4th Bore in California (click on it to enlarge).
Here is the waviness map obtained by using the bar method, which gives the w/L ratio specified for the Caldecott Tunnel. The map is provided on a rolled-out view of the primary lining for the three rounds shown HERE. Additionally, the sphere method may be used to check the criterion on the radius of curvature; e.g., the specifications for the Caldecott Tunnel call for a radius of curvature, R, greater than 200 mm.
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