Yielding mechanism of shallow mass movements in completely decomposed Norwood Tuff: the Zigzag Sign landslide,Utah |
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| Authors: | Aurelian C Trandafir Zahra A Amini |
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| Institution: | (1) Department of Geology and Geophysics, University of Utah, 135 South 1460 East Rm 717, Salt Lake City, UT 84112-0111, USA |
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| Abstract: | Over the past decade, land development activities on hillsides in northern Utah have resulted in a significant increase in
landslide activity throughout the region. The majority of recent landslides are shallow and they occurred on cut gentle slopes
especially during spring and early summer due to snowmelt induced elevated groundwater tables. The geologic material documented
at numerous landslide sites is a soft gray-green completely decomposed Norwood Tuff. The present study addresses the mechanism
of a shallow landslide in completely decomposed Norwood Tuff based on field, laboratory and numerical investigations. Detailed
slope surface geometry obtained from laser-scan surveys together with strength and stress–strain parameters derived from laboratory
triaxial tests on undisturbed samples of completely decomposed Norwood Tuff collected from the landslide site are employed
with finite-element modeling to examine the effects of ground surface deformation patterns on the yielding behavior of the
slide mass. The numerical results indicate a gradual retreat of the yield zone with progressive landslide deformation, which
eventually becomes concentrated within the accumulation zone of the landslide, compared to a well-developed yield zone within
the entire slide mass at the onset of landslide movement. Limit equilibrium stability analyses along potential sliding surfaces
of extent limited within the yield zone of the displaced slide mass produce lower safety factors than an analysis based on
the original sliding surface comprising the entire slide mass. |
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| Keywords: | Shallow landslides Completely decomposed Norwood Tuff Yielding mechanism Finite-element modeling Limit equilibrium analysis |
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