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.
N. Vitharana, A. Gower, G. Bell and N. Petrovic
Churchman Brook Dam is a 26m high earthfill dam with a puddle clay core and impounds a reservoir of 2.2GL. Various remedial works have been undertaken since completion of construction in 1928. In September 2000, a sinkhole in the right abutment was observed during a routine dam inspection. Following this incident, detailed site investigations were carried out. These investigations revealed that there are soft zones and possibly voids formed in the upper part of the clay core.
A comprehensive dam safety study and a risk workshop undertaken in 2002/2003 showed the dam to be deficient in aspects associated with piping, spillway adequacy and outlet works condition. A rational geotechnical model was developed for the foundation utilising triaxial test data from 1980s and recent investigations. The existing spillway chute will be upgraded with a concrete liner attached to the existing chute incorporating no-fine concrete as a free-draining medium. This paper presents the various aspects of the remedial works currently being designed.
Awoonga Dam is the sole source of water for the City of Gladstone and the heavy industries in the region. The area’s distribution reservoirs hold little more than a day’s supply. Extended water supply disruption could have severe economic impacts.
The nine large valves in the inlet tower and river outlet of the dam cannot be inspected or maintained without shutting down the entire water abstraction system. Consequentially limited maintenance has been carried out in the 25 years since the valves were installed.
Recent Dam Safety inspections carried out for the dam owner, the Gladstone Area Water Board (GAWB,) noted some deterioration of the valves and recommended that the valves should be removed, inspected and refurbished as necessary
GAWB was thus presented with a daunting challenge to refurbish valves at Awoonga Dam, as it was generally believed that their removal for refurbishment would not be possible within the time limitations imposed by the system and customer requirements.
In 2008 GAWB commissioned GHD to develop a strategy to refurbish the valves within a 12 hour shutdown period. The strategy proposed and adopted required a rigorous risk management approach and close collaboration between GAWB’s operational staff, two contractors and the consulting engineers. The work was successfully completed during 2011.
This paper discussed the strategies and processes developed and how the project planning, supervision and execution was driven by the risk management based approach. It also highlights some of the experiences and lessons learnt during the project.
2011 – Refurbishing Outlet Valves utilising Shutdown Periods
Since the research and development work carried out by the (then) Metropolitan Water Sewerage and Drainage Board for the strengthening of Manly Dam in 1979/80, there has been over twenty years of continuous improvement in the application of advanced post-tensioned anchors for gravity dam rehabilitation.
Up until the Manly Dam remedial works, concerns had been increasing as to the long-term viability of available anchors. Sophisticated monitorable and restressable anchors, with superior corrosion protection afforded by greased and sheathed strands, were developed initially in test-bed conditions. This style of anchor has subsequently been used extensively throughout Australia on dam upgrades.
This paper compares the claims made by the designers with the demonstrated outcomes of installations that have been achieved, with particular emphasis on dams now owned by the Sydney Catchment Authority and Sydney Water Corporation. The original commitments to economy, aesthetics and rapidity of construction have been borne out by experience, with additional environmental advantages also being achieved. With the confidence built up from many successes in the strengthening of older dams, the time appears right to revisit the construction of new dams using the same style of post-tensioned anchors as the primary stabilising force.
Conrad Ginther, Colleen Stratford
The Wyaralong Dam Alliance (WDA), a consortium of seven engineering and contracting companies, was contracted to design and construct the Wyaralong Dam, which impounds the Teviot Brook 14 km from Beaudesert in Queensland, Australia. The dam is an approximately 500 metre long, 48 metre high Roller Compacted Concrete (RCC) structure built on a foundation generally consisting of massive sandstone with intermittent conglomerate zones consisting of cemented gravels, mudclasts and sands. Geologic features of note with regard to dam stability and long term seepage at the site are dominated by downstream sloping bedding features and conglomerate zones. In addition to the bedding-related features, two predominant vertical to subvertical fracture sets exist. The condition of the vertical fractures ranges from tight and fresh at depth to highly weathered and filled with dispersive clay and gravels near the foundation surface. To provide a durable and effective long term seepage barrier for the dam, an extensive foundation cleaning and treatment operation was undertaken. This comprised drilling, blasting, and excavation of the majority of the highly weathered rock and dispersive materials supplemented by localized installation of small cut-offs and dental concrete and the construction of a double-line grout curtain installed using real time computer monitoring, the GIN methodology, and balanced, stable grout mixes.
Foundation Preparation and Seepage Barrier Installation at Wyaralong Dam Construction Project