Importance of Site-Specific Dynamic Soil Properties for Seismic Ground Response Studies: Ground Response Analysis

Importance of Site-Specific Dynamic Soil Properties for Seismic Ground Response Studies: Ground Response Analysis

Shiv Shankar Kumar (Indian Institute of Technology Guwahati, Guwahati, India), Arindam Dey (Indian Institute of Technology Guwahati, Guwahati, India) and A. Murali Krishna (Indian Institute of Technology Guwahati, Guwahati, India)
Copyright: © 2018 |Pages: 21
DOI: 10.4018/IJGEE.2018010105

Abstract

This article highlights the implication of site-specific properties on seismic ground response studies. One-dimensional equivalent linear ground response analysis was carried out using site-specific dynamic properties of locally available soils of Guwahati city, and the results are compared with those obtained using existing strain-dependent dynamic properties. Acceleration time histories from three strong motions were used. It was observed that an input motion having a higher peak bedrock acceleration, utilizing experimentally obtained dynamic soil properties, exhibits 38% and 24% lower peak ground acceleration and peak spectral acceleration, respectively, in comparison to the results obtained using standard VD-SI soil models. The amplification characteristics of the strong motions are observed to be significantly influenced by the degradation of damping ratio beyond 1% shear strain. The results highlight the necessity of conducting GRA of any region considering its regional dynamic soil properties to obtain more realistic outcomes.
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Introduction

In seismic Ground Response Analysis (GRA), the effect of local geology is significantly important since the response of any structure, subjected to the vertically propagating horizontal shear waves, depends on the regional seismicity, source mechanism, geology and local soil conditions (Boore 1972; Kramer 1996; Nath et al. 2013; Kumar et al., 2014a, 2014b). The bedrock motions get amplified or de-amplified within the soil stratum and, therefore, the estimation of dynamic soil properties of the subsurface of any site, prior to conducting the GRA, is extremely important. GRA is one of the important step to foresee the potential consequences of earthquake motion prior to the earthquake occurrence. Several GRA methodologies (such as linear, equivalent linear and non-linear) are available to evaluate different response parameters of the site (Kramer, 1996). The response spectrum at various layers of a stratified soil deposit, obtained as an outcome of GRA, are useful for earthquake based design of geotechnical structures. Almost all methodologies require strain dependent dynamic properties of soils, in terms of the shear modulus reduction and damping ratio curves, as the essential input parameters (Kumar et al., 2017a). Several researchers have performed GRA for Indian cities using DEEPSOIL (Hashash et al., 2016) and SHAKE2000 (Ordonez, 2000), as summarized Table 1. GRA for Guwahati city has been reported by Kumar and Krishna (2013) and Basu et al. (2017) using existing material model proposed by Seed and Idriss (1970) for sandy soil, Vucetic and Dobry (1991) for clay soil, or Ishibashi and Zhang (1993) for sandy and clay soils. Since these soil models have been established for the soils of different regions and of different compositions, the direct adoption of the same may not be suitable for the regional soils considered in the present study. Although the existing soil models were used by Kumar and Krishna (2013), Basu et al. (2017) and Kumar et al. (2017b), the use of dynamic soil properties of regional soils were not reported in the earlier literatures. Shukla and Choudhury (2012) have recommended the use of actual dynamic soil properties for more realistic outcomes from GRA. It can be stated that, in the absence of proper site-specific dynamic soil properties, use of existing soil models might lead to inaccurate estimation of the parameters involved in the earthquake resistant designs.

Table 1.
Material curves commonly used in GRA studies
Material CurvesProposed ByUsed for GRA BySoftware
Gravel
Rock fill
Rock
Seed et al. (1986)
Gazetas (1992)
Schnabel (1973)
Ranjan (2005)
Ranjan (2005)
Boominathan et al. (2008)
SHAKE2000
SHAKE2000
SHAKE91
Clay SandSun et al. (1988)
Seed and Idriss (1970)
Ranjan (2005)
Boominathan et al. (2008)
Anbazhagan et al. (2010)
Govindaraju and Bhattacharya (2011)
Phanikanth et al. (2011)
Shukla and Choudhury (2012)
Kumar (2012)
Kumar and Krishna (2013)
Kumar et al. (2014a, 2014b)
Naik and Choudhury (2013)
SHAKE2000
SHAKE91
SHAKE2000
DEEPSOIL
DEEPSOIL
SHAKE2000
DEEPSOIL, SHAKE2000
DEEPSOIL
DEEPSOIL
DEEPSOIL
Kumar et al. (2017b) SHAKE2000
Clay and Sand Ishibashi and Zhang (1993) Basu et al. (2017) DEEPSOIL

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