In some situations, it is suggested to extend the top layer(s) of geogrid in a wall design beyond the standard 60% of the wall height.
In seismically active areas or with any type of loading above the wall, including slopes and surcharges, top layers of grid should be lengthened to 90% of wall height or an additional 3 ft (0.9 m), whichever is greater. In the event that an interference may exist with the top layer based on other structures in the reinforced zone it is acceptable to move this extended layer to a lower grid elevation at the top of the structure.
The portion of wall above the top layer of geogrid should be reviewed as a gravity wall taking into account all soils and surcharge parameters. (ref. BP, Chapter 12.4)
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