Numerical Study of the Effect of Non-Horizontal Soil Layering on Seismic Response of Semi-Sine Hill

Document Type : Research Article

Authors

1 Assistant Professor, Department of Civil Engineering, Faculty of Engineering, Qom University of Technology, Qom, Iran

2 Associate Professor, Faculty of Geology, University of Tehran, Tehran, Iran

3 M.Sc. Student, Department of Civil Engineering, Faculty of Engineering, Qom University of Technology, Qom, Iran

4 M.Sc. Graduate, Department of Civil Engineering, University of Urmia, Urmia, Iran

Abstract

Seismic resonance assessment of the site and its relationship with ground structures play an important role in
earthquake engineering and risk assessment. Seismic waves can be exacerbated by sudden geometric changes due to
topographical effects, significantly. Various parameters can be involved in the evaluation of topographical
complications. Finally, the effect of all these factors should be summed up and considered in seismic designs. Boore
was the first to use the Finite difference method to examine the triangular hill under SH waves. In this paper,
FLAC2D software is used to analyze the topography of semi-sine hill under Landers earthquake record. FLAC2D
software is a Finite difference program of Itasca software that is used for continuous environments. Each topography
is drawn to investigate the effect of layering of complication materials at angles of 15, 30, 45, 60 and 75 degrees
with a height of 20 m layered and to investigate the effect of height at heights of 10, 20 and 30 m and also with
changing the angle from 15 to 75 degrees. Also, increasing the number of layers in topography with different angles
of 15 to 75 degrees and investigating the effect of placing layers with loose and dense materials is considered. Most
of the time, numerical analysis of a new problem always begins with the simplest behavioral model. Material
behavior here is assumed like most previous studies that considered the behavioral model of materials as linear
elastic model. An important factor that affects numerical results is the layering angle of the hills. Therefore, semisine
hills with different layering angles (15 to 75 degrees) exposed to the Landers earthquake with alluvial
frequency related to each model are modeled with layers that have different properties in terms of density and shear
wave velocity and Poisson ratio. The ratio of maximum displacement of the desired point in the model with
topography to the maximum displacement of the desired point in the reference model here is expressed as
amplification (ah). Increasing the angle of the layers increases the topographic displacement amplification. The
presence of layering with impedance difference in the site causes seismic waves to be caught and increases the
effects of the site. At each layering angle, the height increase is equivalent to an increase in amplifications. In this
way, a model with a height of 30 m, in all angles, has the most displacement response. At all angles, as the number
of layers increases, the amplification of the topography is added. In the three-layer hills with increasing angle, a
wider surface area of the hill is composed of materials with the lowest shear wave speed, which along with the
complexity of layering these hills, has increased their amplification. The impact of how to place loose and dense
non-horizontal layers on seismic motion intensification is the last parameter studied in this paper. It can be said that
there is a relationship between topographical and stratigraphy resonance, and in particular, stratigraphic effects have
a greater impact on the characteristics of earth's motion than topographical effects. By comparing the obtained
results, it was found that each of the parameters of layering angle of topographic materials, height, and number of
layers and the positioning of loose and dense layers in semi-sine geometry are the components affecting the seismic
response of the site.

Keywords

Main Subjects

References

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History

  • Receive Date: 15 May 2022
  • Revise Date: 24 September 2022
  • Accept Date: 02 November 2022

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