SAFETY PERFORMANCE OF DAMS IN CHILE’S HIGHLY SEISMIC ENVIRONMENT


earth embankment. The dam foundation consists of fluvial deposits in the central area of the dam, colluvial deposits, and/or alluvial terraced deposits in the right abutment and intrusive rock (granodiorite type) in the left abutment.


The dam was raised following the downstream construction method, through continuous hydraulic deposition of tailings sands containing no more than 18% fines (material passing ASTM 200 mesh). The inclined deposition surfaces were compacted by tandem bulldozers and smooth vibratory rollers, with 1:3.5 (V:H) to 1:4 (V:H) downstream slopes. Tailings placement stopped at the end of 2008.


Static and pseudo-static stability analysis using limit equilibrium methods were performed. The deformations under seismic loads were estimated by carrying out different methods: the pseudo-dynamic analysis proposed by Makdisi & Seed (1978), and the formal numerical analysis using FLAC2D and FLAC3D. Both numerical analyses did not show any evidence of failure by shear resistance or excess of deformation that could affect global stability. The design earthquake (MCE) was of Ms = 8.3, with the epicentre 123km from the dam at 23km depth, with a PGA of 0.37g (horizontal) and 0.25g (vertical) in hard soil. The 16th


September 2015 earthquake of Mw = 8.4 was at the same depth and remarkably close to the epicentre of the design earthquake. According to the post-earthquake inspection by the Engineer of Record, no significant deformations or instability was detected[44].


7. Design Criteria, Practice and Legislation


For many years in Chile there was no written design criteria and recommended practices, nor any specific legislation applied to the design, construction, and maintenance of dams. Dam engineering in the country in many cases followed the experience of institutions and engineering companies from Europe and North America. The creation in 1887 of the Ministry of Public Works (MOP), and the establishment of a state-owned electric company in 1943, were important milestones in Chilean dam engineering. After 1930 soil mechanics was starting to develop as an engineering discipline, and post-1940 a series of local engineers travelled abroad to study postgraduate courses on this discipline, thus reinforcing the capacity of local institutions. In the country there were no local norms or legislation that regulated dam design and, in general, the recommendations and guidelines from international organizations were followed. As part of the seismic dam design the international recommendations were followed, basically verifying the seismic stability of dams through a pseudo-static approach applying


seismic coefficients Kh and Kv. For many years, a value of Kh = 0.10 was applied for most dams. For the design of Rapel concrete arch dam in the 1960s a Kh = 0.12 was used[45] . The discussion on which is the reasonable value to be used has been going on for years and


no definitive answer has ever been obtained[46]. Since the 1970s the most used values of Kh varied from 0.15 to 0.20. In 1975 ICOLD[45] insisted that the seismic stability of dams


should consider a dynamic approach as already proposed by some researchers in the UK and the US[47,48]. ICOLD insisted on the need for proper seismological studies to define the seismic


Vol XXXI Issue 3 DAM ENGINEERING 229


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