For hydropower dam projects, design and construction of the temporary works including cofferdams are very important. Improper selection, design and/or construction of temporary works may cause delay of major construction works and increase construction cost.
The authors worked on the preparation of the Engineering, procurement and construct EPC tender (based on International Federation of Consulting Engineers (FIDIC) contract-yellow book) for a 20 MW Hydro Power Plant (HPP) project in the Balkans Region. The scheme involved the design and construction of three cofferdams to enable construction of the main dam, intake and powerhouse. The basis for tendering, as a part the contract documents, was the preliminary design of the HPP scheme. The tenderers were allowed to deviate from the solutions presented in the preliminary design as long as the proposed solutions fulfilled the Employer’s Requirements.
As a part of a winning strategy, the preliminary design cofferdams were changed and modified, providing significant saving and facilitating quicker and safer construction. This paper presents the development of the design and challenges faced during construction work.
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This paper provides an outline of the design and construction of the works undertaken to refurbish the 120 year old intake tower at Mundaring Weir. The project drivers included asset condition, hydraulic capacity, reduction in unusable storage, and reduction in evaporation from the reservoir. The one off sale of this water together with the present value of the reduction in evaporation pays for the project construction and is a significant response to climate change that is taking place in the region. The effects of Alkali Aggregate Reaction (AAR) compromised the efficacy of the Intake Tower operating as a dry-well, while the small diameter and significant corrosion of cast iron pipes and valves had severely diminished the service capacity of the structure. The solution implemented in this project included: lining the Intake Tower with a 37 m long by 2.7 m diameter 316 stainless steel liner; construction of a new inlet 15 m below the reservoir surface using a bespoke underwater coring rig; relining of existing pipes through the dam wall; and new outlet control pipework and valves downstream of the dam.
Many mapped faults in the south-eastern highlands of New South Wales and Victoria are associated with apparently youthful topography, suggesting that faulting may have played a role in shaping the modern landscape. This has been demonstrated to be the case for the Lake George Fault, and may reasonably be inferred for the poorly characterised Murrumbidgee, Khancoban, Tantangara, Berridale Wrench and Tawonga faults. More than a dozen nearby major faults with similarly youthful topography are uncharacterised. In general, fault locations and extents are inconsistent across different scales of geologic mapping, and rupture lengths, slip rates and other fault behaviours remain largely unquantified. A more comprehensive understanding of these faults is required to support safety assessments for communities and large infrastructure in the region.
Kangaroo Creek Dam is a concrete face rockfill dam (CFRD) located on the Torrens River, approximately 22 km north east of Adelaide. The dam is currently undergoing a major upgrade to align it with updated safety guidelines set by the Australian National Committee on Large Dams (ANCOLD) to better withstand major flood events or earthquakes. As part of this upgrade, external omega-type waterstops have been installed on the vertical and perimetric joints to mitigate the impact of expected joint deformations due to seismic loading. Two profiles were selected for the external waterstops; one capable of extending 200 mm for the perimetric joint and the outer two vertical joints on each side, and one capable of extending 100 mm for the remaining vertical joints and the horizontal joint between the new face slab and the original face slab. Using the external omega-type waterstops as the second waterstop for the extended perimetric joint simplified construction, particularly with respect to reinforcement details adjacent to joints. It is understood that this is the first time in Australia that an omega-type waterstop is being fitted to a CFRD slab. This paper demonstrates the benefits of retrofitting waterstops to existing dam joints when required, provides general installation details, details for providing a continuous barrier with the existing waterstops by overlapping internal and external waterstops, and lessons learnt from the waterstop installation.
Global climate change will amplify existing risks, as well as create new risks for natural and human systems. Recent climate changes have already had widespread impacts on human and natural systems. Dams provide a range of economic, environmental and social benefits including irrigation, flood control, water supply, hydroelectric power, recreation and wildlife habitat and play an important role in human settlement. Adapting into the effects of climate change is vitally important for future management of dams. This paper uses the recent drought and floods in Victoria to illustrate the importance of considering the effects of climate change in design, operations, maintenance and emergency management of dams.
On February 7, 2017, the gated service spillway (also known as the Flood
Control Outlet or FCO Spillway) at Oroville Dam was being used to release water
to control the Lake Oroville level according to the prescribed operations plan.
During this operation, the service spillway’s concrete chute slab failed, resulting
in the loss of spillway chute slab sections and deep erosion of underlying
foundation materials. Subsequently, as the damaged service spillway was
operated in an attempt to manage multiple risks, the project’s free overflow
emergency spillway was overtopped for the first time since the project was
completed in 1968. Significant erosion and headcutting occurred downstream of
the emergency spillway’s crest structure, leading authorities to evacuate about
188,000 people from downstream communities.