Seismic Analysis of an Existing Earth and Rockfill Dam Subjected to the MCE by FLAC

Seismic Analysis of an Existing Earth and Rockfill Dam Subjected to the MCE by FLAC

Author: Orlando Román, Solange Paihua, Rubén Vargas
Conference: Tailings and Mine Waste 2016
Date: October 2-5, 2016

In recent years the height of the tailings facilities has increased significantly; also, in contrast to water dams, tailings dams are built by successive raisings, which can be take place by using different materials and even different raising methods in one single dam. These characteristics could make an advanced modeling of dam seismic behavior necessary when the problem becomes complex or the consequences of failure are high, especially in seismically active areas where major earthquakes are expected. The studied tailings dam, located in the southeast of Peru, is planned to be raised up to 90m high, with the feature that some previous stages were raised by the upstream method; therefore, a portion of the embankment is currently supported by old potentially liquefiable tailings.

This paper presents the 2D dynamic analysis of an earth and rockfill dam subjected to the maximum credible earthquake (MCE) using the software Fast Lagrangian Analysis of Continua (FLAC) and the UBCSAND constitutive model for the characterization of the tailings. The main purposes of the analysis were to predict a satisfactory behavior of the dam crest, to estimate the global permanent displacements and to assess the influence of the tailings liquefaction in the seismic performance of the dam. The final results obtained after successive analyses on the dam configuration are presented here. The new raising uses the centerline method considering rock-fill berms as reinforcement in the upstream slope, and flattened slopes on the crest in order to reduce damages during the earthquake.

This paper presents the dynamic analysis executed in an earth and rockfill dam for a tailings facility located in southeast Peru. Currently, the dam is at an elevation of 4475masl, with a maxi-mum height of 75m and a crest length of 342m, and will be raised until reaching the elevation of 4490masl with the centerline method whereby the dam will reach a height of 90m and its crest length will increase to approximately 440m.

The main reason of the geotechnical design was to evaluate the physical stability of the dam considering the application of seismic loads under which the dam could be subjected to in the long term. To do this, the seismic behavior of the dam was evaluated using the MCE.

The specific purposes to carry out this analysis were: (1) to verify the behavior of the crest so that its serviceability was not compromised after the design seismic event, (2) to verify the behavior of the tailings dam due to the liquefaction of the tailings disposed upstream of the center-line raising and previous stages raised by the upstream method (up to an elevation of 4460masl) and (3) to evaluate the permanent global displacement through the foundation of the dam.

The 2D dynamic analysis of the tailings dam was carried out using a FLAC numerical modeling in order to use an approximation of the performance design, which requires determining the deformations induced by the earthquake.


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