This report documents the flow failure of the Las Palmas tailings dam that was induced by the 27 February 2010 Maule Chile M8.8 earthquake. The Las Palmas site is located in Central Chile in Region VII near the town of Talca. Construction of the tailings dam occurred between 1998 as part of a gold mining operation and was no longer in active use.
The ground shaking from the earthquake induced liquefaction of the saturated tailings material and resulted in a flow failure that ran out upwards of 350 m, flowing downslope in two directions. This report is broken into three sections:
- A summary of the construction and flow failure of the Las Palmas tailings dam;
- Details on the field investigations at the site, including the 2010 GEER reconnaissance, 2011 litigation support [DICTUC 2012], and the recent PEER–NGL-funded 2017 investigation; and
- Back-analysis of the flow failure by Gebhart [2016] to estimate the residual strength.
The goal of this work is to provide a “high-quality” flow-failure case history to augment the existing database. The existing database is composed of roughly thirty case histories of varying quality (e.g., Weber et al. [2015] and Kramer and Wang [2015]). Herein, the term “high-quality” means that the in situ measurements were made in a controlled and repeatable manner, and that the back-analysis of the residual strength was performed considering static and dynamic effects of the slide mass. The results from this research indicate that the median back-analyzed residual strength of the liquefied material is ~8.3 kPa (~173 psf) at a pre-earthquake vertical effective stress of 2 atm (~200 kpa or 4000 psf), which is correlated to a median SPT blow count of N1,60~2.5, a median CPT tip resistance of qc1~1.3 MPa, and a median shear-wave velocity of VS1~172 m/sec. The back analyzed residual strength has a nominal coefficient of variation of 5.5% determined using a sensitivity analysis.
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