Pérez-Rivera, Esteban

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    Numerical evaluation of seismic soil pressures on rigid walls
    (2014) Pérez-Rivera, Esteban; Montejo-Valencia, Luis A.; College of Engineering; Suárez-Colche, Luis E.; Ramos-Cabeza, Ricardo; Department of Civil Engineering; Acosta-Lugo, Maribel
    This study focuses on the analysis of the dynamic soil pressures developed on a rigid retaining wall when subjected to seismic excitations. This is a topic of large controversy on the engineering community because current analytical approaches can lead to significantly different pressure distributions and design actions. Current code methodologies include the simplified Mononobe-Okabe Method (Seed and Whitman 1970) for yielding walls. For rigid walls, current codes have adopted the Wood (1973) static “1g” loading analytical solution and the numerical procedure proposed by Ostadan (2005). Despite being developed under the assumption of a yielding wall, the M-O method is commonly used in practice for the estimation of seismic pressures in rigid walls. When used for rigid walls, the pressures resulting from the M-O method are usually considered as a lower boundary for the actual pressure distribution in the retaining structure. Contrary to M-O Method, the Wood (1973) solution for rigid walls is deemed to be very conservative and is usually considered as an upper boundary for the actual pressure distribution in the retaining structure. The most recent simplified method adopted by design codes and standards like ASCE4-09 and NEHRP (2009) is the one proposed by Ostadan (2005). This method was aimed to take into account the effect of wave propagation in the soil, the non-linear response of the soil and the characteristics of the input motion. Nevertheless, recent experimental results from centrifugal tests do not agree with current code expressions. To tackle this problem in this research work a finite element model was developed using OpenSees to capture the response of a rigid retaining wall and the surrounding soil during an earthquake event. This allowed us to implement an incremental dynamic analysis (IDA) to comprehensively: (1) examine the effect of the soil non-linearity for a dry and non-cohesive soil profile in the induced soil pressures due to earthquake loading, (2) evaluate current code equations/methodologies by comparison with the results from the numerical model and (3) examine the effects of input motions with different characteristics (records compatible with a deterministic earthquake scenario and records compatible with a uniform hazard spectrum) in the induced seismic pressures. It was founded that the magnitude of the seismic pressures and design actions obtained from the numerical model are between the predicted by the M-O and Wood methodologies. While the shape of the induced seismic pressures was found to be significantly different, the design action values (shears and moments) from the Ostadan approach were found to be in relatively close agreement with the results from the numerical model. The results from the IDA confirmed that soil nonlinearity and seismic wave amplification play an important role in the response of the soil-wall system; therefore methods that assume constant acceleration along the soil deposit and/or characterize the input motion solely based on its peak acceleration may lead to inaccurate pressure estimates.