Alberto Scuero, Gabriella Vaschetti, John Cowland
Waterproofing geomembranes have been used for new construction and rehabilitation of dams since 1959. Research for underwater rehabilitation with geomembranes started at the beginning of the 1990s. The first installation was made in 1997 at Lost Creek arch dam in USA, where a SIBELON PVC geomembrane system was installed partly underwater, to restore watertightness to the upstream face. Techniques for underwater cracks/joints repair, and for staged repair, were developed and first adopted in 2002 and 2010 respectively. The paper presents through some significant case histories the range of underwater applications available today. The paper also presents a new underwater technology, the Sibelonmat®mattress, that allows water-tightening canals without reducing water flow.The Sibelonmat®can be used in embankment dams, to waterproof the upstream. face or as upstream blanket
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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.
Gavan Hunter, David Jeffery and Stephen Chia
The Main Embankment at Tullaroop Dam in central Victoria is a 43 m high earthfill embankment with a very broad earthfill zone and rockfill zones at the outer toe regions. There has been an extensive history of cracking within the Main Embankment since formalisation of visual inspections in 1987.Widespread cracking has been observed on the crest and downstream shoulder. Cracking on the crest has mainly been longitudinal, but transverse cracks have also been observed. Cracking on the downstream shoulder has comprised longitudinal, diagonal and transverse cracking. In April 2004, a 60 mm wide diagonal crack opened on the downstream shoulder of the left abutment (from crest to toe) and Goulburn-Murray Water constructed a local filter buttress in 2005/06 on the left abutment. In 2011/12 a longitudinal crack opened up on the upper downstream berm toward the right abutment. The crack was initially 15m long and 10 to 215 mm wide, then propagated several months later to 70 m in length, 40 to 50 mm width and greater than 3 m in depth.In May 2011 three piezometers within the earth fill core recorded a very rapid rise in pore water pressure equivalent to 12 to 13 m pressure head above their previous readings. The piezometers were located on the same alignment (upstream to downstream) and were located below the crest and downstream shoulder, and the rise was to levels close to and above the embankment surface. The piezometers then showed a steady fall with time returning to the pre rise levels after 4 to 6 weeks.In 2015/16 Goulburn-Murray Water undertook dam safety upgrade works to reduce the risk of piping through the Main Embankment by extension of the filter buttress across the full width of the embankment. During these upgrade works, very deep (greater than 5 m) and extensive transverse cracks were observed in the embankment over relatively subtle slope changes on the right abutment.Thecracking and pore water pressure behaviour in the Main Embankment at Tullaroop Reservoir present an important case study. The paper provides details on the cracking and postulated crack mechanisms, and the rapid pore water pressure rise and postulated mechanisms. A summary of the upgrade works is also provided.
Barton Maher and Michael Peel
The Queensland Bulk Water Supply Authority (Seqwater) manages up to $12 billion of bulk water supply infrastructure and the natural catchments of the region’s water supply sources to ensure a reliable, quality water supply for more than 3million consumers across the region. Seqwater was formed on 1 January 2013 through a merger of three State-owned water businesses, the SEQ Water Grid Manager, LinkWater and the former Seqwater. Seqwater delivers a safe, secure and reliable water supply to South East Queensland, as well as providing essential flood mitigation services and managing catchment health. Seqwater also provides water for irrigation to about 1,200 farmers and offers community recreation facilities enjoyed by more than 2.5 million people each year.Seqwater owns and operates 26 referable dams which fall under the dam safety regulation in Queensland, 51 weirs, and two bore fields across the region. Twelve key dams across the region supply as much as 90% of South East Queensland’s drinking water.In 2011, Seqwater engaged a consultant team of URS (now AECOM) and SKM (now Jacobs) to undertake a portfolio risk assessment of the 26 referable dams and Mount Crosby Weir. At the completion of the project in December 2013 there were 12 dams with life safety risks assessed as being above the ANCOLD and DEWS Limit of Tolerability. A $6.2 million investigation was approved in 2014 to commence planning for the recommended dam safety upgrades and reduce uncertainties in the risk assessment.This program of work was completed in late 2016. The estimated costs of the identified dam safety upgrades exceed $900 million.Confronted with such a large capital program, Seqwater has instigated a number of key actions including:-benchmarking capital investment and rates of risk reduction achieved by other dam owners through a dam owners group-developing a dam safety investment policy to provide a clear guidance on the framework for prioritising and scheduling upgrades-undertaking targeted investigations to reduce uncertainty in the risk assessments including the use of detailed consequence assessment-preparing a prioritised schedule of planned upgrades to gain endorsement from Government and the Dam Safety Regulator. This paper presents the outcomes of the Portfolio Risk Assessment and key changes to the initial risk assessment following further studies. The basis for the dam safety investment policy is presented and the proposed prioritisation tools.The impacts of the risk assessment provisions in the most recent revision of Queensland Acceptable Flood Capacity Guidelines for Water Dams are also discussed. In particular,the application of the economic criteria for determining the minimum upgrade required by the Queensland Dam Safety Regulator and its relevance to other dam owners.
Shayan Maleki, James Apostolidis, Tom Ewing, Virgilio Fiorotto
The stability analysis of dam spillways and stilling basin chutes requires the knowledge of the spatially fluctuating pressure at the bottom of the structure with reference to the large vortex system with dimensions comparable with the structure characteristic length of the order O (0.1 –1 m). In this context only the small frequency pressure fluctuations (smaller than 1 –10 hz in prototype) must be analyzed in Large Eddy Simulation (LES)context; while the higher frequency pressure fluctuations could be filtered given their negligible importance in relation to stability computations with reference to the spatial Taylor macroscale and fluctuating pressure variance evaluation. These two quantities allow us to define the variance of the force acting on the structure, and as a consequence via statistical analysis, the design force on the structure. This procedure is historically performed via.physical hydraulic modelling (PHM)where these quantities are measured in a laboratory setup. Considering the limits of.current industry approach to Computational Fluid Dynamics (CFD), the use of Detached Eddy Simulation (DES) could become a valid low cost solution and could potentially be a valid method to perform preliminary studies in order to refine the design while avoiding expensive physical model modifications. In this paper, the pressure field at the base of a rectangular impinging jet is measured in laboratory flume setup and is compared with the numerical results obtained via equivalent DES simulations conducted in CFD.Maximum values and the structure of spatial correlation of the anisotropic field of fluctuating pressures are described in view of their relevance to the structural design of the lining of spillway stilling basins and other dissipations structures,as well as in view of their relevance to rock stability analysis. The comparison of the laboratory study with DES simulations presented in this paper shows a good agreement indicating.that this approach may eventually provide a lower.cost substitute for physical model studies in the design of stilling basins and plunge pools.However,it is acknowledged that virtually all stilling basins and plunge pools present a three-dimensional hydraulics complexity, and numerous.further studies need to be done.
Paul Somerville, Andreas Skarlatoudis and Don Macfarlane
The 2017 draft ANCOLD Guidelines for Design of Dams and Appurtenant Structures for Earthquake specify that active faults (with movement in the last 11,000 to 35,000 years) and neotectonic faults (with movement in the current crustal stress regime, in the past 5 to 10 million years) which could significantly contribute to the ground motion for the dam should be identified, and be accounted for in the seismic hazard assessment. The purpose of this paper is to provide guidance on the conditions under which these contributions could be significant in a probabilistic seismic hazard analysis (PSHA)and a deterministic seismic hazard analysis (DSHA).We consider five primary conditions under which identified faults can contribute significantly to the hazard: proximity, probability of activity, rate of activity, magnitude distribution, and return period under consideration