Remedial Works at Troneras and Miraflores Dams in Colombiaby Fabio Villegas, Integral S.A., Medellin, Colombia,
Document Type: Proceeding Paper
Part of: Geotechnical Practice in Dam Rehabilitation
The 38 m high Troneras and the 55 m high Miraflores earth dams were built in the period 1959-1965. The dams are composed of residual soils and founded on a deep residual overburden. Significant problems developed during construction related to the high water content of the soils and the short construction seasons. The dams were designed following current professional practice (mostly American) in the fifties. Since about 1971 concern about safety prompted preliminary reviews of dam conditions. Some particular circumstances made the dams more susceptible to damage by strong earthquake, namely: 1) the high water content of the soils; 2) the deep residual soil foundation; 3) some loose alluvial deposits left under the Troneras dam; and 4) the working under pressure of the main collector drain of the Miraflores dam. Final design for rehabilitation of the dams was carried out in 1989 and construction of the works executed between 1990 to 1992. Works for the Troneras dam include: (1) an addition to the counterweight fill at the downstream toe; (2) construction of drains and a reinforcing buttress fill at the downstream side of the dam, which raised the crest 3 m; and (3) increase of the spillway capacity. Works for the Miraflores dam include: (1) excavation of a 200 m long drainage gallery into the right abutment residual soil; (2) construction of a deep drainage trench across the full width of the downstream dam shell; (3) construction of a network of shallow drains in the downstream counterweight fill; and (4) lowering the normal reservoir operating level by 5 m.
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