| dc.description.abstract | Experiences from recent earthquake records all over the world suggest that
reinforced soil slopes provide better resistance to the seismic forces and possess
higher yield accelerations compared to unreinforced slopes. While the design and
practice of geosynthetic reinforced soil slopes has reached a level where the basics are
well established and the procedures are standardized, the seismic designs still lack
complete understanding of concepts and principles that alter the performance of the
slope during seismic episodes. This thesis presents results from shaking table tests on
geosynthetic reinforced soil slopes subjected to cyclic base shaking to understand the
influence of various parameters that govern the performance of these slopes during
seismic events.
A uniaxial shaking table was used in the study and reduced scale model slopes
were built in a laminar box and were subjected to sinusoidal base shaking, varying the
frequency and acceleration of base shaking in different tests. Various series of
shaking table tests were carried out to study the effects of shaking acceleration,
frequency of shaking, fines content in soil, type and quantity of reinforcement and
slope inclination on the response of model slopes in terms of acceleration
amplifications and horizontal displacements. Acceleration of shaking was varied
between 0.1g - 0.3g and frequency was varied between 1Hz - 16Hz in different tests.
The frequency of testing was much below the natural frequency of the slopes. Two
soils, a clayey sand with 44% fines content and a poorly graded sand with no fines
were used to study the effect of fines content on the slope response. A geotextile and a
biaxial geogrid were used to study the effect of type of reinforcement and
reinforcement was placed in single, two and three layers in different tests to study the
effect of quantity of reinforcement. Slope inclination was varied as 45, 60 and 75.
While understanding the influence of reinforcement parameters, soil gradation and
slope angle, tests were carried out at different accelerations and frequencies, to
investigate the influence of these parameters under different ground shaking
conditions.
Results from shaking table tests revealed that among all the parameters
studied, soil gradation has greater influence on the seismic response of the
unreinforced as well as reinforced soil slopes. Slopes made of sand without fines
showed highest acceleration amplifications and displacements. While the slopes made
of clayey sand showed higher displacements at higher frequency levels, exhibiting
progressive failure, slopes built with cohesionless sand showed higher seismic
response at low-frequency high-amplitude motions, exhibiting sudden flowslide type
of failure. Inclusion of reinforcement did not have significant influence on the
acceleration amplifications, but the displacements were drastically reduced by
reinforcing the slopes, the beneficial effect more pronounced in case of slopes made
of sand without fines. Among the two types of geosynthetics used in the study, both
were equally effective in reducing the deformations, the different being not
significant. Results showed that reinforcement saturation occurred in the models at 2
layers, beyond which further increase in reinforcement did not influence the response
of the slope. The catastrophic flowslide occurred in unreinforced slope at low
frequency shaking in case of sand without fines is completely arrested by reinforcing
the slope with three layers of geotextile and the deformations were reduced by about
92% for that case, indicating the importance of soil reinforcement in mitigating
seismic hazards. Increase in slope angle resulted in increase in deformations but the
acceleration amplifications remained unaffected. Steeper slopes benefitted more by
the inclusion of reinforcing layers. Displacements computed using Newmark’s sliding
block method agreed reasonably well with the experimental measurements. | en_US |
