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Winchester, MA, United States

Verdugo R.,University of Chile | Sitar N.,University of California at Berkeley | Frost J.D.,Georgia Institute of Technology | Bray J.D.,University of California at Berkeley | And 5 more authors.
Earthquake Spectra

The 27 February 2010 Maule, Chile, earthquake occurred during the driest time of the year, which implied that most of the soils in the slopes were not saturated and that the dams had extra freeboard. This may explain the small number of slope failures caused by the earthquake. However, two important earth dams suffered seismically induced permanent ground movements, but no catastrophic damage was reported because the reservoirs levels were low. Five medium-sized mine tailings dams failed due to liquefaction; one of them tragically caused four casualties. Retaining structures of all types performed well and no failures were observed. © 2012, Earthquake Engineering Research Institute. Source

Urzua A.,Inc. 57 Westland Avenue | Christian J.T.,Prototype Engineering Inc. | Silva R.,Compania Minera Dona Ines de Collahuasi | Bonani A.,Gerente recursos mineros y desarollo
Engineering Geology

The horizontal seismic loading coefficient is an essential input in evaluating the seismic adequacy of slopes, such as those in open-pit mines and natural slopes. In some cases, the coefficient is established through dynamic finite element analyses, which are time-consuming and require a new analysis for each facility, including a new suite of accelerograms. The values of the coefficient are sometimes incorporated in design manuals, but the procedures for establishing the values are seldom transparent. The usual situation is that the values arise from consensus, experience, and previous practice. In this paper, the Urzúa-Christian model for normalized sliding displacement has been extended to develop the critical acceleration value corresponding to the probability of observing prescribed amounts of sliding displacement. The method has been applied to two sets of data based on probabilistic seismic hazard analyses. The results show that, to satisfy the criterion that there must be 0.1 probability of the sliding displacement exceeding 100. cm if a maximum credible earthquake (MCE) occurs, the critical acceleration must be approximately 0.13. g. This means that a slope with these parameters in this environment must be stable enough that a horizontal acceleration of 0.13. g is necessary to put it in a state of sliding motion. In the case of the operational basis earthquake (OBE), which is a much smaller ground motion, the criterion of 0.1 probability of 100. cm of sliding is achieved for a slope with a critical acceleration of 0.35 g. © 2014 Elsevier B.V. Source

Urzua A.,Prototype Engineering Inc. | Christian J.T.,Prototype Engineering Inc.
Engineering Geology

Empirical studies of earthquake ground motions have developed relations between sliding displacement and acceleration ratio and other parameters such as Arias intensity. Computations using strong motion records from the Maule 2010 Chile M=. 8.8 earthquake indicate that the published relations do not conform well to the computed displacements, and some tend to be unconservative. Extensions to the empirical equations incorporating Arias intensity are, if anything, less accurate. These results suggest that these empirical relations may not apply to subduction zone events and indicate that further study using records from other recent subduction zone events is appropriate. Examining the analytical solutions for sliding displacements induced by sinusoidal shaking and the definition of Arias intensity leads to an improved normalization for sliding displacements. When this improved normalization is applied to the records from three different earthquakes in different parts of Chile, the results are nearly identical, and the results for the Chi Chi and Northridge earthquakes are very close to those from the Chilean events. Suggestions for practical use of the new normalization relations are provided. © 2013 Elsevier B.V. Source

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