Richard R. Davidson, Roger Vreugdenhil and Mark Foster
Significant cracking was observed on the crest of the main embankment at Lake Eppalock for many years, but in recent years increasing movement upstream during low reservoir levels indicated a progressively deteriorating stability situation. Investigations also revealed cohesive filter material that would allow a crack to propagate. A fast-tracked remedial works program was completed in 1999 to rebuild the highly vulnerable upper rockfill shells and filters, both upstream and downstream. To manage construction risk, the works were carried out directly by G- MW with innovations in removal, protection and replacement of the downstream shoulders, and placement of a new multi-zone filter.
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B. A. Cole
In October 2000 ANCOLD published a history of dam technology in Australia covering the 150 years in which large dams have been constructed in this country. The paper describes how this project began, the search for authors, the way the authors tackled their tasks, the peer reviews which resulted in additional chapters being written, and the archive searches for interesting photographs to illustrate the text. All this was accomplished by dam engineers including the editor. Then follows an account of the professional publication process: sub-editing, desktop publishing, proof-reading, the preparation of an index, the cover design and the printing process. Some conclusions are drawn from this first experience of book publishing.
P.J. Ritchie and N.A. Currey
Kidston Gold Mines commenced operations in 1984 and built a dam to safely store the tailing waste from the ore processing. The dam was progressively raised 5 times (3 downstream and 2 centreline lifts) and has an active surface area of 310 hectares; stores 66 Mt of tailing and is 32 metres high at its maximum height. The dam was decommissioned in September 1997.
Rehabilitation planning for the tailing dam commenced in 1994 with an 11 hectare direct revegetation trial established in March of that year. A 40 ha trial was established in 1998. Both sites have been the subject of intensive scientific research by the (University of Queensland) Centre for Mined Lands Research group. This research assisted in understanding the issues of revegetation stability and sustainability, biological cycling, soil chemistry and surface erosion.
The aims of rehabilitation is to meet the Queensland Department of Mines and Energy (DME) key closure criteria. These include; creating a stable landform, not only for the dam wall structure but also of low surface erodibility, maintenance of acceptable downstream water quality by controlling poor quality seepage and runoff and by meeting an acceptable final end land use criteria for the structure.
Ongoing research is addressing the long term hydrology of the tailing dam with an aim towards understanding the overall water balance. Three consulting groups are involved in what is considered to be a novel approach. Evapotranspiration rates from pasture and tree species have been measured during the 1999 wet and dry season. This information, along with climatic and soil suction data is then used as one of the key parameters for the unsaturated zone modeling. One output from the “Soilcover” model is seepage into the saturated zone in the tailing dam. Water movements in the saturated zone are being modelled using Modflow. The acid oxidation potential for the dam is also being evaluated in light of the long term water movements in the saturated and unsaturated zones of the dam. This process will allow short and long term prediction of dam seepage quality and quantities.
The geotechnical stability of the final dam wall structure as defined by the Factor of Safety, ranged from 2.0 to 2.3, which meets the long term DME recommended stability target FOS of 1.5 for slopes.
In order to evaluate the impact of metal toxicities in grazing cattle, a grazing trial has been established on the pasture covering the surface sediments of the tailing dam. This work is being supported by the Qld EPA, Qld DME, Qld Health and the NRCET, and will assist in understanding metal uptake in grazing animals on rehabilitated mined lands.
Steven Fox, Garry Fyfe
This paper describes some key details of the construction of the Lake Eppalock Main Embankment Remedial Works Project. This $8.25 million earthworks project was completed on a “live” storage to an accelerated program. As the dam owner Goulburn-Murray Water took the decision to directly manage the construction of these works with resultant benefits in timing, risk management and project management costs.
M. B. Barker, R.M. Holroyde, J Williams and T. Qiu
Grahamstown Dam is a major water supply source for the Newcastle area and it is proposed to raise the full supply level by 2.4m from RL 10.4m to RL 12.8m. The present spillway is inadequate to pass the PMF without overtopping of the existing embankments at the new FSL and part of the raising comprises construction of a new embankment of about 10m high with a right bank spillway upstream of the existing spillway capable of passing the PMF. The Pacific Highway is located some 600m downstream of the new spillway and a 60m wide culvert below the Pacific Highway is being constructed with capacity sufficient to pass the PMF. Significant changes were made to the feasibility design for the spillway and the Pacific Highway culvert using a labyrinth spillway and a baffle chute energy dissipator respectively. Both of these designs are uncommon and the process of finalising the designs as well as some of the problems in the use of a labyrinth spillway and the cost savings realised in the use of these designs are presented.
A.J. Crichton, A.W. Ford, and J.T. Williams
Developments in finite element analysis software are allowing more scope for their use in the stability review of Australia’s ageing dam population. Until recently, model simulation of structural discontinuities were outside the scope of routine dam safety assessment. Current state of the art finite element software puts complex joint modelling tools within the reach of the practicing dam engineer.
This paper describes the use of non-linear finite element techniques to assess the structural adequacy of the Julius Dam, a 26.5 m high multiple arch buttress dam in North-western Queensland. This structure impounds 127,000 ML behind its 399 m crest length for the Mt Isa water supply. The assessment of the structural adequacy included using non linear contact elements to model the sliding between adjacent arch barrels. Contact elements are able to simulate friction on an interface by allowing force transfer by friction under compression with no tensile strength. This tool is invaluable for assessing formed joints or defects within existing structures, as is demonstrated in the paper.