Issue and Nonissue in Block Walls as Implied Through Computer-Aided Design - Reinforced Soil Engineering: Advances in Research and Practice - page 84

Figure 1 Metal strips wall: (a) as designed (uniform L of 5.50m; see calculated Fs-
pullout in Table 1); (b) length producing Fs-pullout ¼ 1.5 at each elevation (see Table 1
for S h ).
the same vertical spacing as the strips of metal (i.e., 75 cm apart, typically an
excessively large spacing in block wall structures).
Figure 2a shows the required layout. Figure 2b shows the length needed to
produce a pullout factor with a safety 1.5. Pullout for continuous reinforcement is
significantly shorter than that for the strip reinforcement. This is apparent when
the required lengths are compared for the same Fs (e.g., Figs. 1b and 2b). Table 2
shows the (conservative) default design data used to assess the geosynthetic
pullout data. Note in Table 2 that for uniform reinforcement length, the actual Fs
for pullout for the geosynthetic layers is extremely large.
When a typical vertical spacing is specified (say, 40 cm), the pullout
resistance is even larger. This resistance is typically large even if the coverage
ratio, Rc, drops to as low as 0.5. For continuous reinforcement, changing the
interaction coefficient to a low of 0.5 would have marginal effect on the overall
required reinforcement length. Clearly, pullout is not an issue for geosynthetic
reinforcement. Furthermore, the effort associated with “exact” characterization
of interface properties through expensive pullout tests seems to be practically
unwarranted. Use of a default length value of 1.0m in block walls should be
sufficient for all practical purposes, even if this value is not ascertained by
Figure 2 Geosynthetic wall: (a) designed using same geometry, soil, and vertical
spacing as metal strip wall (uniform L ¼ 5.5m; r ¼ 28.4 degrees; see Table 2) ; (b) length
producing Fs-pullout ¼ 1.5 at each elevation.