Equivalent-linear seismic analyses of MSW landfills using DEEPSOIL Deepankar Choudhury ⁎, Purnanand Savoikar Department of Civil Engineering, Indian Institute of Technology Bombay, Powai, Mumbai 400 076, India abstract article info Article history: Received 21 August 2008 Received in revised form 14 May 2009 Accepted 16 May 2009 Available online 23 May 2009 Keywords: MSW landfills 1-D equivalent linear analysis Seismic response Normalized stress Seismic accelerations Responses of municipal solid waste (MSW) landfills during earthquakes are gaining worldwide importance due to the devastating nature of earthquake on landfills. Apart from the post-earthquake safety and serviceability issues which pose environmental and public health problems, other important concerns are related to the behavior of closed landfills during and after earthquake. In present study, one dimensional (1-D) equivalent-linear analysis was carried out to model the behaviour of MSW landfills subjected to seismic base accelerations using the DEEPSOIL software. Influence of foundation types, height and stiffness of MSW landfills and seismic base accelerations on the seismic responses in terms of surface accelerations, normalized stresses (i.e., shear stress/effective vertical stress) and spectral amplification are evaluated. The results showed that height and stiffness of landfills, type of foundation and amount of seismic base acceleration and period play important role in evaluating the seismic responses of MSW landfills. Assumption of constant unit weight and shear wave velocity for landfills underestimates maximum horizontal acceleration (MHA), normalized shear stresses and spectral amplification at the top of landfills. Landfill models with smaller heights (up to 40 m high) showed higher amplification ratio for low seismic base accelerations with mean period near to that of soil and landfill resonance for all sites. A complex behavior was observed at higher seismic base accelerations due to non-linear behavior of landfill materials. © 2009 Elsevier B.V. All rights reserved. 1. Introduction Municipal solid waste (MSW) landfills are generally huge structures covering a large surface area with the heights varying from 10 m to more than 150 m. These landfills may be resting on different types of foundation material like rock, sand or clays. They may be founded at ground level or partly below ground or may be founded within canyons. Though there exists both lined and unlined landfills, growing environmental concerns for the contamination of soil and water bodies due to the release of leachate, have made mandatory to provide geosynthetic liners for landfills both at base and at top covers also. Several failures of landfills have occurred in past under static conditions, e.g., those occurred at Rumpke landfill in Ohio (Schmucker and Hendron, 1998), Kettleman Hills waste landfill in California (Mitchell et al., 1990), Payatas landfill in Philippines (Merry et al., 2005), or Leuwigajah landfill — Bandung, Indonesia (Koelsch et al., 2005). Nevertheless, the seismic behavior of landfills is also very important, especially in seismically active zones (Krinitzsky et al., 1997). This is because the dynamic loading induces relative movements within the waste mass and the foundation, which results into rupture of bottom liner or cover system and disrupts the function of leachate and gas collection system, ultimately leading to failure of these landfills. However, seismic behavior of landfills gained importance only after 1987 Whittier Narrows earthquake (M w =6.0). Environment Protec- tion Agency in United States (USEPA) installed two strong motion instruments at base and top deck of Operating Industries Incorporated (OII) landfill in California to measure three-components of seismic accelerations. Observational database of landfill performance during 1989 Loma Prieta earthquake, 1992 Landers earthquake and 1994 Northridge earthquake has provided greater insight into seismic performance of municipal solid waste (MSW) landfills. It can be seen from this database that the modern landfills have demonstrated a good ability to withstand strong earthquakes (of at least 0.2 g) without failure or damages to human health and environment (Augello et al., 1995). Behavior of solid waste landfills during earthquakes can be analyzed by either mathematical or experimental methods. Mathe- matical methods include pseudo-static analysis, permanent seismic deformation analysis and dynamic analysis using computer programs like SHAKE91 (Idriss and Sun, 1992), SHAKE2000 (Ordonez, 2000), DMOD (Matasovic and Vucetic, 1995), QUAD4M (Hudson et al., 1994), etc. using finite element techniques. Experimental methods in performance evaluation of solid waste landfills during earthquakes are available in literature by using shaking table tests (Yegian et al., 1995) and centrifuge model tests (Thusyanthan et al., 2006). In the numerical analysis of MSW landfills, Bray et al. (1995) assumed a constant unit weight, making vary shear wave velocity and shear strength parameters with depth, to model the seismic Engineering Geology 107 (2009) 98–108 ⁎ Corresponding author. Tel.: +91 22 2576 7335 (O) 8335 (R); fax: +91 22 2576 7302. E-mail addresses: dc@civil.iitb.ac.in, dchoudhury@iitb.ac.in (D. Choudhury). 0013-7952/$ – see front matter © 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.enggeo.2009.05.004 Contents lists available at ScienceDirect Engineering Geology journal homepage: www.elsevier.com/locate/enggeo