LUIS VALENZUELA P, RAMON VERDUGO A, JOSE CAMPANA Z & CARMEN G OPAZO A
loads to be applied. The first seismic dynamic analysis carried out in Chile using artificial earthquake and finite elements was for Colbún dam (116m high) in 1974[49], and has continued to be applied to many other dams since.
Legislation on dams (mainly earth dams) started in Chile with a 1981 review of the Water Code, which gave the responsibility of approving dam projects to the Dirección General de Aguas (DGA). In 2015 it issued the present decree N°50 of DGA[50] that established the requirement of pseudo-static and dynamic seismic stability analysis for dams with a height of over 30m. For dams with heights between 15m and 30m only pseudo-static analysis is
required. This decree established the following minimum safety factors (SF): SFstatic ≥ 1.4; SFpseudostatic ≥ 1.2 and SFpostEQ ≥1.0. Currently for large dams the maximum credible earthquake is required to be considered. There were no specific requirements for tailings dams until the
failure of El Cobre dam in 1965. In 1970 a special decree – N°86[35] – was issued jointly by the DGA and Sernageomin. This decree banned the construction of upstream tailings dams, being the first country banning a specific type of dam. The most recent legislation relating to tailings dams in Chile is Decree N°248[36], which replaced Decree N°86 in 2007, and it establishes special conditions for sand tailings dams. The percentage of fines in the sand cannot be higher than 20% passing N°200 mesh.
The “upstream tailings dams” commonly built in Chile before 1965 have no compaction, poor or non-existent cycloning of tailings, steep downstream slopes and an uncontrolled rate of dam raising. Chilean legislation has not recognized other possible upstream construction procedures as is the practice in other countries[51,52].
For all types of dams, except the banned upstream tailings dams, dam design and construction in Chile have considered international best practices as they are developed, following recommendations from organizations like ICOLD, ICMM, CDA, MAC and others.
8. Conclusions
The Chilean territory located just above the collision between the Nazca and South American plates is among the most seismically active region on the planet. Indeed, in the last 70 years Chile has been subjected to 23 strong earthquakes of magnitude M ≥ 7.5, five with M ≥ 8.0 and one of magnitude 9.5 (the largest ever registered in the world). The epicentres of these earthquakes are distributed along the Chilean coastal zones, mainly from North of the parallel 40°S to the Northern border of Chile approximately parallel to 18°S, which coincides with the territory where most aforementioned dams have been built. Considering how narrow the Chilean territory is (200km average width), all the dams constructed have experienced more than one strong earthquake. This is probably the most challenging natural scenario in which a large number of dams of different types have been tested.
This study allows us to conclude that in general, despite the numerous strong earthquakes which have occurred in the last 70 years, the behaviour of Chilean dams has been remarkably good, except in those cases in which evident inadequate design and/or construction was adopted.
230 DAM ENGINEERING Vol XXXI Issue 3
Page 1 |
Page 2 |
Page 3 |
Page 4 |
Page 5 |
Page 6 |
Page 7 |
Page 8 |
Page 9 |
Page 10 |
Page 11 |
Page 12 |
Page 13 |
Page 14 |
Page 15 |
Page 16 |
Page 17 |
Page 18 |
Page 19 |
Page 20 |
Page 21 |
Page 22 |
Page 23 |
Page 24 |
Page 25 |
Page 26 |
Page 27 |
Page 28 |
Page 29 |
Page 30 |
Page 31 |
Page 32 |
Page 33 |
Page 34 |
Page 35 |
Page 36 |
Page 37 |
Page 38 |
Page 39 |
Page 40 |
Page 41 |
Page 42 |
Page 43 |
Page 44 |
Page 45 |
Page 46 |
Page 47 |
Page 48 |
Page 49 |
Page 50 |
Page 51 |
Page 52 |
Page 53 |
Page 54 |
Page 55 |
Page 56 |
Page 57 |
Page 58 |
Page 59 |
Page 60 |
Page 61 |
Page 62 |
Page 63 |
Page 64 |
Page 65 |
Page 66 |
Page 67 |
Page 68 |
Page 69 |
Page 70 |
Page 71 |
Page 72 |
Page 73 |
Page 74 |
Page 75 |
Page 76 |
Page 77 |
Page 78 |
Page 79 |
Page 80 |
Page 81 |
Page 82 |
Page 83 |
Page 84 |
Page 85 |
Page 86 |
Page 87 |
Page 88 |
Page 89 |
Page 90 |
Page 91 |
Page 92 |
Page 93 |
Page 94 |
Page 95
