The Appin Upper Canal is a critical part of Western Sydney’s water supply system. Dating from 1888, the canal continues to take water 58 km from the Upper Nepean to Prospect Reservoir. The Appin Colliery lies under part of the canal infrastructure at Simpson’s Creek, near the township of Appin.

PSM was engaged to assess and mitigate the potential impacts on the canal and associated infrastructure due to underground mining.

Due to drought and other water storage issues, Sydney’s water supply was an extremely sensitive political issue. Maintaining the integrity of Sydney’s water supply was paramount.

The ability to collaborate with an interdisciplinary team of mining, structural, geotechnical, water, subsidence and heritage engineers and communicate with multiple government agencies, including Department of Heritage and Environment and NSW Department of Works and Services, was also critical.

Engineering and technical opportunities included:

• Maintaining the integrity of the canal system during mining while being sympathetic to a heritage infrastructure
• Accurately predicting the impacts on surface infrastructure due to the extraction of long walls 3m high, 290m wide, 1 to 3 km long and 2 to 300m below the surface.

PSM’s tailored approach included:

• Extensive field investigations and geotechnical mapping
• Numerical modelling of the canal and tunnel integrity in 2D and 3D
• Design and supervision of remedial works
• Design of contingency strategies in the case of water supply disruption to reinstate supply within seven days
• Preventative works before extracting one of the mine’s longwalls to avoid damage to the canal through surface ground movement
• Training of inspectors to recognise the signs of movement from mining works
• Participation in a multidisciplinary risk assessment team to develop a qualitative and quantitative assessment plan.

As a result of high-level collaboration, communication and technical expertise, the client gained approval to mine with no disruption to Sydney water supply during direct undermining.

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