| Projects
preventing massive black-outs arising from the sudden loss of large generation capacities. The Ulu Jelai project, in particular, is ideally suited to provide these functions due to the high geodetic head presented by the site’s natural topography.” Working in the tropical and isolated environment in the Cameron Highlands, located 140km north of Malaysia’s capital city, Kuala Lumpur, presented its own unique challenges. Building access roads to the project site and tunnelling through 23km of rock was a challenging undertaking due to the remote location, tropical climate and uncertain geological conditions, including deep weathering of the rock and fault lines. The main dam of the Ulu Jelai Hydroelectric Project
is located on the Bertam River, but the project also utilizes the flow from two adjacent river catchments being diverted into the main reservoir. The scheme generates 326GWh of energy annually, which contributes to Malaysia’s power supply system and helps to meet the surge in demand at peak hours. “This is a project that we have taken through the full cycle,” remarks Andreas Neumaier. “From feasibility review to tender design to construction and commissioning and connection into the Malaysian power grid.”
Tunnelling and geotechnical
challenges “From a tunnelling perspective, this project was particularly challenging,” comments Luke Drowley, Manager Geotechnics and Tunnels, who worked for three years as Lead Tunnel Engineer on the project. The power station caverns are located around 240m below surface level. Due to this significant depth, it was not possible to undertake extensive geotechnical borehole drilling to confirm a geological model and the parameters for the design of underground works. “We relied on a combination of expert knowledge and specialist testing to continuously refine our understanding of the rock structure and the tectonic stresses in the rock,” explains Drowley. This information was then incorporated into the design of the rock support system for the excavated power station caverns.
Another significant challenge was the design of an unlined headrace tunnel. As Ulu Jelai is intended to provide peaking power, the plant is expected to start and stop rapidly, especially when performing frequency control to Malaysia’s national power grid. Full turbine opening or closure can occur within five seconds, resulting in rapid changes in hydraulic pressure. The headrace tunnel, which is around 4200m long, was designed as ‘unlined’, where long-term support is provided by a combination of durable rock bolts for structural support and a relatively thin layer of shotcrete for erosion protection.
Designing such a pervious tunnel lining system was
a technical challenge. “We had to ensure that water loss would not lead to reduced electricity generation capacity for the scheme and that the rock mass would be strong enough to withstand these rapid fluctuations in water pressure, without the lining or surrounding rock becoming dislodged or damaged,” explains Drowley. “We also used 3D modelling to better understand the geometrical constraints, and to ensure that
the geometry and loadings of the mechanical and electrical equipment were compatible with the civil structure,” adds Mike Yee, Hydropower Engineer. Three-dimensional computer modelling was also used to space-proof the power station with the cavern excavation, and to generate the construction documentation to build the power station structure. “It was important that technical expertise was supported and aided by technology to achieve strong outcomes,” he adds.
Designing within a complex and
daunting environment “As with many large hydropower projects, once we started uncovering the foundation, there were issues that required complex adjustments and design solutions,” says Dilwyn Jones, Senior Dams Engineer. “We found the foundation was weathered in some places and had many faults in a closely jointed rock mass, which raised concerns about the stability of the dam foundation.”
Significant design changes were made to Susu
dam to develop solutions for the faulted foundation and related concerns about the strength and water- tightness of the structure. One particular challenge was shifting from the high cementitious content roller compacted concrete (RCC) that was originally proposed, to a low cementitious content alternative combined with an impervious geomembrane attached to the upstream face of the dam.
“It became clear that we needed to shift the design philosophy to a low cementitious content RCC mix to provide a more ductile structure capable of accommodating the variations in the foundation rock,” explains Jones. “This solution was complex, it meant rewriting specifications during construction, and implementing a number of other design changes such as an external grouting plinth. However, it ultimately offered a lot of benefits, improving the resilience and the structural integrity of the dam, and reducing the leakage potential through the dam body.” “Personally, I feel proud of the immense amount of work and technical expertise that went into modifying the dam design to render it safe, despite the faulted foundation. It was also an amazing opportunity to work with world experts in RCC dam construction and dam safety.”
Coordinating civil, electrical and
mechanical works On a project of this scale, it is critical to coordinate the work between the civil and the electrical and mechanical works contractors to ensure that the equipment delivery and installation schedule match the civil construction schedule, minimising the time to commissioning. Delays to civil works required the careful management of this process. Electrical and mechanical installations included all necessary auxiliary systems for the main plant, the underground cavern and the surface installations. In addition, key safety-related systems in the underground power station including the ventilation, firefighting and detection systems were designed to ensure the safety of personnel and equipment in the event of an emergency. “The ventilation system needs to f
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Above and below: Cavern and internal structures of the 372MW hydroelectric project
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