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September 20, 2019

Ok Tedi – A Mine In The Clouds

Since January 2018, we’ve been involved in an exciting project with our client GR Engineering Services.

It’s been a mix of everything – severe earthquake loading (including an earthquake during design!), huge rainfalls, restricted access, tie-ins to structures that due to the highly corrosive nature of the site were in part non-existent, congested reinforcement, the list goes on.

We worked literally alongside the GR team using our “Engineers On Tap” model to provide instant access and response throughout the project.

It’s exciting to see the construction proceeding now. Our Principal Structural Engineer, John Zhang recently visited the site to assist with some of the tie-in challenges and has prepared a summary of our involvement for your reading pleasure.

Project Background

Ok Tedi mine commenced operations in 1985, making it the longest-running open-pit copper, gold and silver mine in Papua New Guinea. On a national level, it contributes more than 7 per cent of GDP to the PNG Economy. The current life of mine plans see production continuing until at least 2024, and potentially beyond 2030 with an increase in resource and reserve inventory.

A significant portion of the increased reserve material will be sourced from a cut-back of the east wall of the pit. This will require the existing crushing circuit to be removed and replaced which has developed into the Crusher Replacement Project (CRP).

Conveyor Segments
One of the conveyor segments being craned into position

GR Engineering Services (GRES) was awarded an EPCM contract in 2018 for the provision of engineering services to complete the detailed design of the CRP for client OTML. Yenem Engineering Services, as a subcontractor of GRES, was engaged to provide the structural design for this project.

There were many challenges encountered on this project, and the major challenges are outlined as below from engineering perspectives:

Project challenges

1. Engineering and environmental challenges

The level of seismic loading in PNG is significantly higher than commonly encountered in Australia. Earthquake hazard assessments have been undertaken in PNG since the 1960s but most early studies were based on limited data. Little earthquake hazard work has been done within the country over the past ten years, a period that has seen significant development in earthquake hazard methodology in other regions. Therefore, except for determining base shear from PNG’s seismic response spectrum, we chose to carry out earthquake design in accordance with Australian Standards and relevant international standards methodologies.

Ok Tedi copper concentrate pipeline
A magnitude 7.5 earthquake struck Papua New Guinea in 2018. Pictured is landslide and damage to Ok Tedi’s copper concentrate pipeline caused by earthquake.

Part of the new conveying circuit will be founded on tailings at Ok Ningi valley, which may cause unexpected settlements. In some areas, geotechnical advice suggests settlements to be a couple of hundred millimetres. Pile foundations and soil stabilisation have been applied in the design to minimise the settlement issues.

Old Ok Ningi Dam
Old OK Ningi Dam

The scale of this project is very significant. We’ve designed over 13,000 m3 of concrete and over 2,500 tonnes of fabricated steel in order to construct the new facility. The mine is on the 2094 m high Mount Fubilan. Local road systems exist only as a result of the mine, while river transport provides the most access. The maximum capacity of the batching plant is less than 150 cubic metres per day. We have adopted a modular construction approach as much as possible. We have designed retaining structures with steel and gabions rather than the concrete. These have significantly reduced the construction time and minimised the amount of works on site.

Ok Tedi New Crushing Circuits
New Crushing Circuits

Rainfall is around 9 000 mm at the mine site. The mine site experiences only 25 rain-free days each year. This means sufficient drainage diversions, sediment control structures and pipeline.

It’s definitely been a challenge but not one too great for the joint team of GRES & Yenem!

Here Are Some Of the Progress Photos Of The Project

Ok Ted Mine Work Progress Photos

OTML makes a significant economic contribution to PNG and assists in the development of economically sustainable local and regional communities.

“It’s been a fantastic project, particularly recognising our involvement in the growth of an economy not just the expansion of a company’s profits.”

John Zhang,
Principal Structural Engineer

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