Nikifor Petrovic, Sladoljub Pezerovic
Dam rehabilitation works at the Visegrad Hydropower Project on the River Drina in Bosnia and Herzegovina were completed in October 2014 after two years of very challenging and collaborative effort between the client, designer and contractor.
The successfully accomplished remedial works programme was a highly complex geotechnical intervention. The dam was constructed on a karst foundation extending up to 200 m below reservoir floor level. Rates of seepage through the foundation increased over time, from 1.4 m3/s following first impoundment in 1989, to 14.7 m3/s in 2009.
The rehabilitation works comprised:
Preparatory works (site installation, work platforms, conveyer belts, electricity and water supply, drilling and grouting equipment installation);
Site investigation works (drilling of boreholes, measurements of inclination, geo-physical carotage, downhole video, underwater camera recording);
Installation of monitoring equipment and implementation of real time recording system;
Installation of inert material into a sinkhole within the storage area and into the bore holes located upstream of the dam; and
Grouting of the foundation area using different grout mixes and grouting methods.
During rehabilitation works the main achievements were:
A total of about 37,300 m3 of inert material (granular materials with different fractions from 0 to 32 mm) was installed into the foundation cracks and caverns. This was a significant achievement due to very complex geological conditions and resulted in a seepage reduction through the foundation and improvement of the overall safety and stability of the dam.
The total consumption of grouting material was in access of 2,500 tonnes of cement, bentonite, sand and additives.
After completion of the work, seepage of water through the foundation was reduced to about 4.5 m3/s.
Keywords: Seepage, remedial works, dam, grouting, inert material.
M. A. Hariri Ardebili, M. Akbari and H. Mirzabozorg
This paper presents a study on the effects of incoherence (considering the Harichandran and Vanmarcke coherency model) and wave-passage (considering various wave velocities) on the nonlinear responses of concrete arch dams . A double curvature arch dam was selected as numerical example, the reservoir was modeled as incompressible material and the foundation was modeled as a mass-less medium. Ground motion time-histories were artificially generated based on a Monte Carlo simulation approach. Four different models were considered in the generation of ground motions; Uniform excitation; Just incoherence effect; Just wave passage effect; and finally take into account both incoherence and wave passage effects. It was revealed that modeling incoherency can have significant effect on the structural response of the dam by modifying the dynamic response of uniform excitation and inducing pseudo-static response. Also, it was concluded that incoherency effect overshadow wave passage effect and results caused by wave passage effect are close to the results of uniform excitation.
2011 – Comparison of wave passage and incoherence effects on nonlinear non-uniform excitation of concrete arch dams
T. Mortimer, J. McNicol, P. Keefer, W. Ludlow
CS Energy’s Kogan Creek Coal Mine located in the Surat Basin in Queensland, services the 750MW coal fired, Kogan Creek Power Station. Strip mining generates large volumes of mine waste which is typically used to construct waste dumps. Recent work at the mine has focused on using mine waste to construct an ash storage facility to store ash that is piped over 5 km from the power station as a dense phase slurry. The use of mine waste to construct the ash storage facility provides significant cost and time savings, however a range of design, construction and operation issues needed to be addressed to operate a facility of this type.
This paper describes some of the key design, construction and operation considerations for the ash storage facility. Design considerations include pipeline transport through environmentally sensitive areas, addressing the stability of the embankment and the use of a partial LLDPE geomembrane lining system to reduce the risk of seepage from the storage. Construction considerations include post construction (pre ash deposition) floor treatment to reduce potential settlement. Operational considerations include ash slurry deposition, water management of the decant pond and progressive rehabilitation of the final landform.
2011 – Design, Construction and Operation of a Partially Lined, Ash Storage Facility Constructed from Mine Waste
David R Jeffery
In 2004 the Victorian Government announced the decision to proceed with Australia’s largest dam decommissioning project, the return of the 365,000ML capacity Lake Mokoan to a wetland.
The project has been completed and has resulted in significant river health benefits through liberating environmental flows in the Broken, Goulburn, Murray and Snowy Rivers. Decommissioning has allowed the recovery of water savings for return as environmental flow to the River Murray (30,000 ML/year) and Snowy River (21,000 ML/year).
With decommissioning complete, development of a significant wetland complex across the 8100 hectare site has commenced.
This project has been undertaken at a time when the Broken River basin was exposed to its worst drought conditions in over 100 years and within 11 years of the worst flooding experienced in the nearby Rural City of Benalla. These extremes of climatic conditions and their impacts on the local and irrigation communities have ensured considerable community and stakeholder interest in the decision to proceed with decommissioning and in the subsequent delivery of each of the project elements.
This paper provides an explanation of the drivers for the project, describes the process followed and some of the challenges experienced over the projects seven year life and presents some of the lessons learned along the way.
2011 – MOKOAN – RETURN TO WETLAND PROJECT
G. Hadzilacos, ML. Ng, K. Taske, A. Small and B. Loney
Alteration of flow patterns by constructing a dam may have an irreversible impact on ecosystems depending on the timing, duration and frequency of these flows. As part of an Environmental Impact Study, carried out for a proposed mining operation in Australia that included an earth dam on a pristine ephemeral creek, an appropriate waterway management scheme was proposed that required the establishment of measurable instream flow requirements. This paper describes an environmental flow analysis (EFA) carried out to identify flow regimes that achieve the desired ecological outcomes for the affected waterways. The EFA methodology was based on the range-of-variability approach using a calibrated rainfall-runoff model to form the hydrologic basis. The study established a relationship between flow components and ecological variables based upon which the flow requirements were estimated using a simple methodology.
2011 – A case study of an initial Environmental Flows Assessment for an earth dam on a pristine stream in Cape York