Practice and Research of Geosynthetic Reinforced Soil Walls in Australia - Reinforced Soil Engineering: Advances in Research and Practice - page 252

was found to be significantly less than unity. For high-tenacity polyester, it is
generally in the range of 55-70%. For HDPE, it is in the range of 33-45%. Note
that f m takes into account both uncertainties in material strength and loss in cross-
sectional area. The former is due to manufacturing variability and error in
extrapolating test data to a 100-year design life. The latter is due to construction
damage along with chemical degradation due to the ambient environment.
The above procedure gives T dr as a fraction of the tensile strength measured
in a quick tensile test. There have been debates on the extent of conservatism
inherent in the method used to assess T dr , the long-term design strength. Deriving
T B by the stress rupture method inherently implies a load duration effect. This, in
conjunction with Eq. (1), implies that the geosynthetic reinforcement will be
adequate to carry T*, the factored reinforcement tension, for the specified design
life. However, T*, being a factored value, will not occur throughout the entire
design life. Indeed, it will only occur for short durations. As such, GRS walls may
have been designed with an extra margin of conservatism. Alternative design
methodologies based on the so-called residual strength method (Greenwood,
1996; Lo, 1997) have been debated but have not been adopted due to the
perceived lack of adequate data.
3.3 Modular Block Walls
In Australia, modular block walls are commonly referred to as segmental block
walls. The connection between the blocks and reinforcement is commonly
achieved by sandwiching the reinforcement between two blocks. Dowel pins may
also bear against the transverse member of a geogrid, hence providing additional
connection strength. The practice for SRA projects in New South Wales is to
assess the connection strength based on short-term pullout test data provided by
the specialist GRS contractor or the block manufacturer. The pullout test results
can be idealized as consisting of two segments, as illustrated in Fig. 3 .
The connection strength manifested in the first segment, which manifests
dependence on vertical stress, represents reinforcement pulling out between the
blocks. As such, the as-measured strength of the first segment is taken as the long-
term strength. The connection strength manifested in the second segment is
independent of the vertical stress. It represents the limiting connection strength
due to reinforcement rupture. This limiting connection strength, however, is only
about 50-70% of the T uo . This reduction is believed to be due to the nonuniform-
clamping action from the blocks. Some work has been done on developing more
effective connections, but such design, at the time of writing, has not yet been
used in SRA projects in NSW. To account for the reduction in rupture strength
with load duration, this limiting strength (from segment 2) is reduced by the
factor T dr /T uo , where T uo is the short-term tensile strength of the reinforcement.