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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.

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2015 Papers

2015 – Remedial works to reduce seepage under Visegrad HPP dam
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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.
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2017 Papers

2017 – Sheet Piles: Driving a Solution to Piping Risk
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Tom Ridgway, Chris Topham, Aaron Brimfield

A significant number of dams across Australia are of earthen construction and may be susceptible to internal erosion of their earth core, also known as piping. In January of 2016, during an annual inspection of the Tarraleah No 1 Pond Levee it was found that the embankment was experiencing significant seepage at the toe. Further investigations found actively developing piping holes through the embankment. To better understand the condition of the dam, HydroTasmania’s remote monitoring trailer was deployed to provide telemetered seepage data to further understand the developing issue. It was found that the leakage was increasing dramatically, and carrying suspended core material, resulting in the need for prompt resolution to protect the embankment from further loss of material. A sheet piling wall was installed in the centre of the embankment to cut off the flow of water through the embankment. After the installation of the sheet piling wall, post works monitoring showed the seepage through the embankment reduced to virtually zero, only peaking in rainfall events. This paper outlines the investigation and management of the incident, and the mitigation measures put in place from the time of identification including the use of a sheet piling wall to mitigate a developing piping failure. The paper will conclude with the outcomes of the work and how a similar solution could be utilised for other dam owners in a piping event.
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2020 Papers

2020 – Monte Carlo Geospatial Approach to Liner Design Principles in TSFs
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Gideon Steyl, Ralph Holding, Lis Boczek

A Monte Carlo method for assessing liner systems is applied with outcomes demonstrating the range of discharge that could occur over the liner interface. The Monte Carlo approach allows for variation of fill material over the liner system and includes the assessment of a second compacted zone either above or below the liner zone. In this paper clay liners were evaluated due to regulatory guidelines and it could be demonstrated that similar performance to a 1 m clay liner could be attained using compacted material to reduce discharge over the liner interface. The approach applied in this paper allows for at least a worst-case quantification of seepage risk which could be included in liner selection criteria or presenting liner options to regulators.
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2011 Papers

2011 – Investigating the Piping Risk Associated with Seepage at Monbulk Saddle Dam of Silvan Reservoir, Victoria
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Monique de Moel, Mark Arnold, Gamini Adikari

Monbulk Saddle Dam, built in 1929, is one of two saddle dams located at the southern end of Silvan Reservoir, near the township of Monbulk, Victoria. The saddle dam is a 5.3m high earthfill embankment with a 230mm wide, centrally located, concrete core wall. The reservoir retained is located in the valley of Stonyford Creek, and impounds approximately 40,500 ML of water at FSL.

Excessive seepage at the right abutment of Monbulk Saddle Dam has been an issue since the early 1970’s. The reservoir has been operating with a level restriction since then to reduce the seepage flows. However; this restriction limits the operational flexibility of the storage. Early investigations concluded that the most likely mechanism for these excessive seepage flows was a defect in the concrete core wall.

Melbourne Water Corporation, (the owner and the operator of the reservoir), undertook a risk assessment for Silvan Reservoir as part of a review of its dams asset portfolio. Based on the information then available, the risk assessment was undertaken using the criteria and guidelines developed by ANCOLD. The result was that the piping risks associated with the seepage from the west abutment at Monbulk Saddle Dam was unacceptable. The risk assessment Panel also cast doubt on the likelihood of the seepage being caused by a defect in the concrete core wall. Melbourne Water therefore engaged SMEC Australia to investigate the likely causes and mechanisms for this seepage and to develop suitable remedial measures for the dam.

The investigations have included a desktop review of historical information, test pit investigations, Sonic borehole drilling, dynamic cone penetration tests, an infrared thermal imaging investigation and an electromagnetic groundwater seepage flow mapping investigation.

These investigations have shown that the most likely cause of the seepage is the presence of permeable foundation layers located beneath and around the existing core wall as the core wall does not extend over the full length of the embankment and becomes shallower towards the abutments.

To satisfy the ALARP principle; risk reduction remedial works Concept Designs are being developed and reviewed.

2011 – Investigating the Piping Risk Associated with Seepage at Monbulk Saddle Dam of Silvan Reservoir, Victoria

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