2012 – Seismic Induced Slope Displacement of a Tailings Embankment – Comparison of Numerical and Simplified Analysis Methods
Zhenhe Song, Arjuna Dissanayake, Shunqin Luo
One of the potential tailing dam failure modes that is commonly evaluated is for prediction of earthquake induced crest displacement in relation to available freeboard. The prediction of seismic induced displacement for tailing dams can be evaluated using simplified approaches, i.e. analytical methods by Newmark (1965), Makdisi and Seed (1978), Bray and Travasarou (2007) and empirical method by Swaisgood (2003) and Pells and Fell (2003).
Seismic induced displacements have been estimated using these simplified methods and numerical methods by FLAC and PLAXIS. The results from the numerical modelling were compared with results derived from the simpler analytical and empirical methods. The results indicate the numerical analysis results agrees reasonably well with empirical methods by Swaisgood (2003) and Pells and Fell (2003) and can be used to provide additional confidence in the seismic stability of tailings embankments. However, simplified analytical methods by Newmark (1965), Makdisi and Seed (1978), Bray and Travasarou (2007) could underestimate the seismic induced displacements.
Keywords: Tailing dam, Seismic analysis, numerical analysis, simplified analysis, liquefaction.
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2012 Papers
2012 – Investigation of stilling basin slab stability for Waipapa Dam Spillway, NZ
Learn moreKaren Riddette, Chee Wei Tan, Alan Collins, David Ho
Due to a number of historical stilling basin slab failures around the world, modern basin slab stability assessment approaches now require allowance for hydrodynamic pressure fluctuations. Extreme fluctuations in uplift pressures have been found to occur in hydraulic jumps and plunge pools resulting in high-pressure pulses being transmitted via joints and drainage openings to the underside of the slab. If, peak uplift forces beneath the slab coincide with minimum pressure fluctuations on the top of the slab, the resulting pressure differential can be sufficient to lift a slab. As a result, simple static design based on tailwater depth and mean floor pressures is now considered highly non-conservative.
Through a case study on the Waipapa Dam spillway stilling basin, this paper examines the use of CFD modelling to compute mean hydrodynamic slab pressures taking into account the location of the hydraulic jump and the effect of the impact blocks on the pressure distribution over the slab. By combining the CFD results with empirically-derived pressure fluctuations, uplift scenarios are applied in a FEA model to compute the maximum load in the slab anchors and examine the sensitivity of the stilling basin slabs to uplift failure.
Keywords: Stilling basin, hydrodynamic modelling, CFD, pressure fluctuation, slab stability.
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2012 Papers
2012 – Piano Key Weir: An Innovative Spillway Upgrade Solution
Learn moreMike Phillips, Kelly Maslin
A spillway upgrade conceptual design and selection process was undertaken to identify options for upgrading the Dartmouth Dam to pass the Probable Maximum Flood (PMF). A number of upgrade options were investigated, including variations of dam raise heights and spillway modifications. One of the options, the piano key weir, was initially developed from the limited available publications on the weir design, and further developed with the use of a 1:60 scale model. The piano key weir, a variation of the labyrinth weir, is a passive spillway that utilises a total weir length several times that of the effective spillway width. For the Dartmouth Dam study, the piano key weir design that was developed consisted of a 7-cycle, 9 m high structure, with a total weir length of nearly 600 m, or more than 6 times the existing effective spillway width of 91 m. The spillway was designed to pass the routed PMF outflow of approximately11,500 m3/s with a head of approximately 11 m.
The piano key weir design was developed using the following analyses:
Initial 1:60 scale physical model of the piano key weir based on published papers on piano key weirs and design manuals for labyrinth weirs;
Structural analysis and weir member sizing using initial physical model results;
Computational Fluid Dynamics (CFD) modelling to improve the hydraulic efficiency of the weir for the range of flows;
Revised 1:60 scale physical model of the piano key weir; and
Confirmation of conceptual structure design.
This paper describes the process of developing the piano key weir option for the Dartmouth Dam spillway and lessons learned.
Keywords: Piano key weir, CFD, spillway, physical model
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2012 Papers
2012 – Negotiating the Geological Structure of the Enlarged Cotter Dam Site During the Abutment Excavation Period
Learn moreAndrew Barclay, Greg Kotze
The Enlarged Cotter Dam (ECD) is under construction on the Cotter River, 18km west of Canberra. The new dam comprises an 85m high roller compacted concrete gravity dam, located 120m downstream of an existing 31m high concrete dam. This paper describes the geological structures that prevail at the site and their significance with respect to design and construction considerations.
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Geological mapping has confirmed that the abutment slopes are characterised by zones of prominent rock outcrop and thin mantles of colluvial soil that form overall slope angles of 45 degrees. The Cotter River valley in the ECD area has been eroded through a geological sequence of Early to Late Silurian age, comprised predominantly of porphyritic rhyolite and lapilli tuffs of the Walker Volcanics.
Geotechnical investigations for the ECD were extensive and comprehensive. The results obtained have enabled the compilation of a detailed geological model of the dam site. Particular attention was paid to defining, characterising and kinematically analysing prominent geological structures, including intersecting sheared or crushed seams and zones that traverse the dam footprint.
Prominent geological structures that were encountered during the abutment excavation had significant design and construction implications for:
Abutment stripping and foundation preparations;
Rock slope stabilisation;
The foundation of the intake tower that comprises a 66m high concrete structure; and
The foundations for 1 x 56m high and 2 x 78m high tower cranes that required positioning on the steep abutment slopes during construction.
This paper highlights the importance of understanding the geological origin, nature and distribution of rockmass defects within a complex rock foundation. Site specific construction requirements and engineering design solutions used to successfully negotiate adverse geological structures are described.
Keywords: Dam, Roller Compacted Concrete, Geological Structures, Abutment, Foundation. -
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2012 Papers
2012 – 15 Years of Experience with a Dam Improvement Program
Learn moreShane McGrath, Andrew Reynolds, Garry Fyfe, Chris Kelly, Steven Fox
Goulburn-Murray Water is a rural water corporation located in Northern Victoria. It has responsibility for 12 State dams and is also the constructing authority for the Murray Darling Basin Authority’s Victorian assets.
Over the past 15 years G-MW has been engaged in a dam improvement program across its portfolio. To date 14 individual projects have been undertaken at 11 dams. The total expenditure is $125 million.
Starting from a base level of data at its inception in 1997, the program has encompassed all facets required for a dam improvement program. From early prioritisation to set the investigation program, through design reviews and risk assessments to develop the upgrading program and subsequent implementation. Some elements of the program were at the leading edge of practice at the time and a range of experiences along the way were character building as dam safety investment challenged other corporate priorities.
This paper sets out the lessons learned in developing the methodology and implementing the program of works, particularly relating to corporate adoption of the program, organisational capability, investigations, risk assessments, design and implementation.
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2012 Papers
2012 – We need flood protection in WA too!
Learn moreGraeme Mann, Michael Smith, Louise Thomas
Regular flooding around the coastal town of Busselton, south of Perth, led to the construction of large rural drains in the 1920s to divert two of the major rivers around the town. Hydrologic studies after major floods in 1997 and 1999 showed that the existing drains were providing much less than the desired 1 in 100 AEP flood protection, particularly as subdivisions were being developed along both sides of the Vasse River Diversion Drain (VDD).
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Three compensating basins constructed in rural land south of Busselton provide a total storage capacity of 4.4 GL. The banks that form the three basins have a total length of 8.5 km, vary in height up to 6 m and are either zoned earthfill embankments, with a clay foundation cut-off through sandy soil horizons to a depth of 1 to 2 m below ground level or homogeneous earthfill embankments. The spillways are overflow sections on the embankments using concrete revetment mattresses. The outlet works are uncontrolled box culverts with a capacity of up to 14 m3/s. Peak outflows are typically about 30% of peak inflows to the basins.
The paper discusses the Busselton Flood Protection Project and associated diversion drains, including the design of long embankments for the compensating basins on very flat terrain that are required to survive their “first filling period” during each flood emergency.
Keywords: Earth embankments, flood mitigation, flood compensating basins, levee banks, diversion drains, Busselton, piping failures.