Geoscience Reference
In-Depth Information
Figure 6 Reinforcement strength against time. (From Jewell and Greenwood, 1988.)
The CEN TC 189 committee has produced harmonized test methods on all
relevent tests for geosynthetics. These norms are today the only valid test
methods in Europe. The last norms were approved by the member states in 2000.
The uniformity in testing procedures and documents that state which parameters
engineers must specify with certain uses of the geosynthetic materials is a very
big step ahead on the road to full acceptance of these materials by the civil
engineering world.
There are also material factors that cover for uncertainties in extrapolation,
accuracy of testing, and so on. First introduced by Jewell and Greenwood (1988),
they are now modified and incorporated in BS 8006. To overcome this
uncertainty, a separate factor f m12 is used in BS 8006. Based on the quantity of
tests, time of extrapolations, and so forth, this value can vary between 1.0 and 2.5.
The lower value should only be selected when allowed by approved certifying
bodies after extensive evaluation of the test results.
Figure 6 summarizes the relationship between the rupture strength and
allowable reinforcement force, the design strength, which is a function of the
design life, t d , and the design temperature, T d .
6 STIFFNESS
As stated earlier, the second design requirement is stiffness. Most soil
reinforcement structures will deform to a certain extent only. This design
requirement can be translated into a maximum strain requirement for the geogrids
(BS 8006, 1996). In such a case, the requirement limits the strain during
construction as well as the additional strain occurring during the service life of
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