1578
Proceedings of the 18
th
International Conference on Soil Mechanics and Geotechnical Engineering, Paris 2013
Figure 6. Effect of cycle number on hysteresis loops in a TOSS test.
Typical irregular loading results are shown in Figure 7 where
both the load history and respose are presented. Ramberg-
Osgood models with an extended Masing criteria have been
applied to the input stress history and yielded satisfactory
results. Strain-rate effects will be evaluated as well, however for
these sands, there seems to be little effect. Other soils planned
for testing include soft and stiff clays found throughout the
floodplain and beneath younger sediments along the Danube.
Figure 7. Irregular load history and test result.
4 CONCLUSION, FURTHER RESEARCH PLANS
The RC-TOSS system has shown itself to be a robust, accurate
and reliable testing device. It can perform tests over a strain
range from γ = 10
-4
% to 1% for RC testing and 5x10
-3
%-1% for
TOSS. Shearing stresses can exceed 200 kPa for TOSS and
400-600 kPa for RC. The magnet-coil system is very sturdy and
produces sustained, static torque with only moderate heating.
Resonance testing generally requires much less power and can
perform over the entire strain range. The device is capable of
measuring pore pressure and vertical deflection as well,
allowing for estimates of volume change.
Measurements of shear wave velocity (leading to
computation of shear modulus) have been consistent between
the RC and TOSS methods for the same specimen and same
strain level. Measurements using bender elements have
confirmed the data as well.
In the future further cyclic and irregular tests will be
performed with the RC-TOSS device in order to study the
effects of confining pressure, density and different irregular
load histories. Due to the nature of the control system almost
any sort of irregular loading can be studied; uniform cycles,
uniform with offset, varying amplitudes or even totally irregular
(e.g. any arbitrary earthquake time history). Other soils will also
be tested and test results are planned to be compared to in-situ
measurement results.
5 ACKNOWLEDGEMENTS
The authors acknowledge the financial support of the Széchenyi
István University within the framework of TáMOP 4.2.2/B-
10/1-2010-0010 application.
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