The Nakan Dam, at the Kelian Equatorial Mining gold mine, in East Kalimantan, Indonesia was constructed to store 165 million tonnes of acid waste rock under 1 m of water. The project comprised four earth and rockfill embankments. The high level diversion conduit (HLDC) was built through one of these to provide runoff diversion. The HLDC included an inclined decant system up the upstream face of the saddle embankment with inlets at 10 m intervals to allow for incremental filling of the reservoir during waste dumping. A flow of approximately 50 L/s was observed, when the bellmouths were closed, indicating a leak had developed within the HLDC.
PSM was engaged to permanently seal the leak in the HLDC.
The Nakan Dam is located in a remote region of Borneo, approximately 2 km south of the equator. It experiences high annual rainfall with an operating reservoir level of approximately 30 m head.
Permanent sealing (grouting) of the leak could not be undertaken without temporarily halting or reducing the flow. Working conditions were risky with a potentially low oxygen atmosphere and/or explosive environment within the HLDC and subsequent rise in reservoir level following sealing. The location of the leak within a pipe buried beneath 70 m height of the earth and rockfill embankment was unknown.
Other engineering and technical opportunities included:
Following a rigorous assessment, PSM’s tailored approach included:
PSM successfully permanently sealed a leaking 1 m diameter pipe located beneath a 70 m high earth and rockfill embankment. The design solution incorporated a bespoke 1 m diameter inflatable packer to seal the pipe outflow before displacing the water via a high-flow grouting operation.
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