1 Seismic ground response analysis for soil site in Johor, Malaysia Anurag Sahare and Deepankar Choudhury Department of Civil Engineering, Indian Institute of Technology Bombay, Powai, Mumbai - 400076 ABSTRACT Seismic ground response analysis (GRA) has been carried out for a soil site located in Johor, Malaysia in order to know the degradation of soil layers overlying a bed rock subjected to a ground motion. In this paper, an effort has been made to critically study the results obtained by 1-D equivalent linear analysis and nonlinear analysis using DEEPSOIL v6.1, SHAKE 2000 and D MOD 2000 for different modulus reduction and damping curves with two different soil models. The results are observed to be nearly similar for a lesser depth soil model unlike larger depth soil model, for which the results are slightly different. The results from DEEPSOILv6.1, SHAKE 2000 and D-MOD 2000 are found to be different for a larger depth soil model. Nonlinear analysis is preferred as it takes into account the actual nonlinear characteristics of soil. 1 INTRODUCTION Seismic GRA has been performed in order to estimate the response of local soil layers to earthquake loading in terms of surface accelerations, maximum horizontal accelerations along depth, response spectrum etc. For this, ground response analysis makes use of wave propagation theory in order to estimate the local soil effects on the propagating shear wave originated from the bed rock during an earthquake. Seismic waves after originating from the source propagates in all directions. However it is assumed that the waves travel only in vertical direction from bed rock to the surface for 1-D seismic GRA, which has been used for the present study. During the propagation of seismic waves, the wave characteristics such as amplitude and frequency content gets drastically modified depending on the local soil properties and if the structure is not designed for the appropriate ground motion, it may result into large destruction leading to severe consequences. The pre- requisites for carrying out site specific ground response study is soil model with all soil layers including dynamic properties of the soil as well. The soil properties like unit weight of soil, depth of soil layer shall be provided as input in the soil model. The soil model can be defined based on the bore-log profile of the site representing various soil layers with thickness. The dynamic properties of the soil can be evaluated based on either laboratory tests (cyclic triaxial test, resonant column test etc), field measurements or by using existing correlations with field tests e.g. standard penetration test, Cone Penetration test, Becker Penetration test etc. Mostly it is not feasible to carry out laboratory tests and hence commonly the dynamic properties of soil are evaluated based on certain correlation which has been developed for a particular soil and area of concern. The most commonly used correlations are with SPT N value. Choosing the appropriate correlation for the site is the most important task as it should completely be dependent on the local soil properties. Soil properties drastically vary from location to location. Modulus reduction and damping curves can be obtained by cyclic triaxial testing for the corresponding soil type. In lack of such tests, modulus reduction and damping curves put forward by the researchers for different soil types may be used. Several ground response studies have been carried out in the past for many cities like Phanikhanth et al. (2011) carried out 1-D equivalent linear GRA for typical sites in Mumbai subjected to four strong earthquakes, Shylamoni et al. (2014) carried out 1-D equivalent linear GRA for a Nuclear plant in Japan and the results were observed to be in a very close approximation to the recorded values of most of the aftershocks and Mahmood et al. (2016) carried out 1-D equivalent linear GRA for a collapsed tower in Islamabad. The evaluated spectral acceleration values were observed to be higher than the values recommended by the building code of Pakistan 2 SITE LOCATION The site chosen for the present study is located in Johor, Malaysia. It is an Oil Refinery and Petrochemicals Integrated Development (RAPID) Project. The soil seems to be predominantly silty clayey type of soil with some of the soil layers as sandy soil. Two soil models of significantly different depth are considered in the present research work in order to know the effect of the number of soil layers to ground response. The bore- log data was obtained from one of the reputed geotechnical firm which represents SPT N-value along depth as well as the basic geotechnical properties which were obtained from the laboratory tests. No laboratory or field data information about the dynamic properties of soil was available for the site and hence SPT N value versus shear wave velocity correlation is used in order to estimate dynamic soil properties as proposed by Ohta and Goto (1978), the correlation which has been developed for all types of soil which is represented in equation 1. Vs = 85.35N 0.348 [1]