Caren And Ovejeria Dams, Chile
Since the dynamic behaviour of dams under severe earthquake motion is not known satisfactorily, data from strong motion instruments can form the basis for a more reliable seismic assessment of the existing and future dams. GeoSIG has maintained a strong presence around the world in the form of dam monitoring solutions.
Our partner GeoMediciones / C. Fahrenkrog y Cia Ltda. (www.geomediciones.cl) has achieved a strong position in seismic monitoring systems and associated solutions in Chile and region. The below case study is provided by them in full context and being published here with some minor editions.
Evolution of Sand Tailings Dams in Chilean Mines - A Case Study by GeoMediciones (www.geomediciones.cl)
The great copper mines in Chile have experienced a continuous growth in the mineral production rates in the last 30 years. This, coupled with the low ore yield, has led to a significant increase in tailings production. In addition, the deposits of this mineral are of great dimensions, easily topping the thousand million tons of mineral. All of this indicates that the management and storage of the mine process waste has become significantly important in the design and operation of an existing or a new mine.
The majority of the large mineral deposits in the central zone in Chile are located in the Andes Mountains. The abrupt topography of this area together with a very active hydrology and geodynamics limit the capacity for tailings disposal. This has led to a search for disposal areas with a gentler topography and greater capacity located in the central valley at distance greater than 50 km from the concentrator plant. The vast amount of reserves and the convenience of disposal, whenever possible, at a single impoundment site have made these impoundments to have dams of greater than 100 m in height, and, in some cases, of more than 250 m in height
As a consequence of March 1965 earthquake, the authorities issued in 1970 a norm to regulate the design, construction, and operation of sand tailings dams (Decree No. 86). This norm provided for the first time definitions, criteria, and specifications to be complied with for the construction and operation of impoundments, which required deployment of strong motion instrumentation on tailing dams.
Ovejeria Tailing Dam
The Ovejeira dam took five years to build and has been fully operational since December 1999. It serves Andina for the rest of its estimated 50-year useful life, and includes an 86 km concrete canal to transport tailings from an on-site concentrator plant to the dam, including 22 km of tunnels.Ovejeria receives more than 60'000 tpd of tailings material from Andina, (95% of everything extracted from the mine), which is scheduled to increase by almost to around 244'000 tpd after the mine's next expansion stage.
A configuration of 3 units of GSR-18 Strong Motion recorders with AC-63 Triaxial Accelerometers were deployed, synchronized with GPS for timing, as well as solar panels, charge regulator and large capacity batteries were installed. The measurement locations were at freefield, at dam foundation and at dam crest.
Caren Tailing Dam
Caren Reservoir, located 90 km south west of the city of Santiago, has served since 1986 for the disposal of tailings generated by El Teniente, the largest underground production copper mine in the world. The dam was designed in 12 stages with a final height of about 141 m and it is estimated that by the end of its life the reservoir can store a total of 2,200 million m3 of tailings. As it stands today, the construction of stage 5 ends with a height of approximately 84 m. Approximately 600 million m3 of tailings are already stored in the dam. The lifeterm of the Caren Dam is expected to be between 2054 and 2064, depending on the future rate of generation of tailings, currently at 130'000 tonnes per day.
A configuration of 3 units of GSR-18 Strong Motion recorders with AC-63 Triaxial Accelerometers were deployed, synchronized with GPS for timing, as well as solar panels, charge regulator and large capacity batteries were installed. The measurement locations were at freefield, at dam foundation and at dam crest.
Earthquake Response
On Saturday, February 27, 2010 an earthquake with a Richter magnitude 8.8 occurred in the early morning, on the southern part of Chile, which affected the central region and especially the important cities of Concepción, Talca and the Maule region. For that time 5th was on construction and Ovejeria Dam was in full operation. Immediately, after the earthquake, a complete inspection was performed at all dams, including Caren and Ovejeria dam. Both, the existing dam as the fillings that were placed for the recent stages behaved properly and as intended in the design stages, resulting in no event that would place any doubt on the stability and security criteria set for the dam. Only minor cracks were detected in the crest with openings of 5 to 6 mm near the abutments.
Undoubtedly, the good performance of the dams to this important ground motion will be taken into account in developing the next stages of engineering required for the future.
Conclusions
The steady advance of the state of the art in regards to the dam design, together with the growing need to optimize cost, schedule and ultimately the environment care, has allowed in this case, develop innovative projects that meets the operational requirements for which it was designed. In a country of high seismicity, as Chile, some relevant considerations are made in the design stage about the safety of the work, out of which some of these were developed in this project. Similar deployments are already being planned to be used in other tailings dams from other operational divisions in Chile, having these as references.
Tailing dams are characterized, among other things, with their continued growth over time, depending on the production of the mineral to which they are associated. The production levels are generally increasing, so that innovation and the constant search for solutions should be constantly updated in this field. The scope of the 2 dam projects required instrumentation to record seismic motions and other ambient dynamic activity in order to continuously monitor dam structural safety within the context of a safe operating dam environment.
Once the data has been processed it is assessed and compared as dam behaviour against seismic design criteria applicable to dam operations. The project facilitated the development and improvement of dam emergency and safety measuring equipment within the context of increased awareness and contributed to the regional seismic data management systems.
Summary of systems table of the monitoring solution
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Solution |
Product |
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Sensors |
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Seismic Recorders |
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Central Processing System Centre |
Processing And Reporting Software |