Mittal, Ankur Kumar and B, Umashankar
(2018)
Staged Pullout Testing of Extensible and Inextensible
Reinforcements.
Masters thesis, Indian Institute of Technology Hyderabad.
Abstract
Disposal of waste material like pond ash is a major concern to environment. One of
the possible applications of this type of waste material is to utilize them as backfill
material in reinforced earth structures. To proper design of any reinforced earth
structure, soil reinforcement interactions are important where shear and pullout are
the most common internal failure modes. Pullout parameters have an important role
in design of reinforced earth structure and to determine these parameters pullout test
has been carried out at different samples.
In this study it is proposed to use pond ash and sand as a backfill material so, this
study is carried out to determine the axial pullout resistance of smooth metal strip
reinforcement and geogrids. Pond ash from Narla Tarato thermal plant, Vijaywada,
Andhra Pradesh has been used. Here, a new test method has been developed named
as staged pullout test (SPOT) where a model ground can be tested for two or more
than two normal stress conditions. SPOT has advantage over conventional pullout
test (CPOT) because CPOT requires three or more model ground to get the pullout
properties and it is very difficult to maintain same properties for each model ground
while for SPOT only one ground has been used to get the pullout properties. In the
SPOT, normal loads are in staged condition or changing the normal load after
stopping the test when pullout displacement reaches to 20 mm. In order to
investigate the SPOT method, both CPOT and SPOT have been performed on the
same model ground and results have been compared. From the comparison, SPOT
results of smooth metal strip reinforcement were found to be closer with CPOT
results for 17 kPa and 52 kPa while for 87 kPa SPOT results can be used with a
factor of safety of 1.2. It has been also observed that SPOT results produce
comparable results with CPOT for first 20 mm displacement irrespective of the
reinforcement. For geogrids, logarithmic fitted test results are differ by less than
10% for first 20 mm displacement and 15-20% for remaining displacement up to 60
mm. The percentage change for logarithmic fitted results is going to higher when
moving to higher normal stress conditions. So, SPOT method could be used instead
of CPOT with a factor of safety of 1.2 to 1.3. From the results, SPOT has a
probability to be used as a new pullout test method instead of CPOT.
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