of of

The frictional resistance offered by a geogrid against pullout may be expressed as (Koerner, 1999)

(19.27) where Ci =interaction coefficient =0.75 (may vary)

C r =coverage ratio =0.8 (may vary)

All the other notations are already defined. The spacing of geogrid layers may be obtained from

where Ph = lateral pressure per unit length of wall.