Permeation Grouting of a Subsidence Impacted Watercourse in the Southern Coalfields-Paper

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Longwall mining beneath Myrtle Creek in New South Wales caused bedrock fracturing that diverted water underground, reducing surface flow and the water-holding capacity of pools. Pool 23, a pool held behind a sandstone rock bar, was selected for remediation.<br /><br />A 2019 investigation used ten boreholes, core logging, caliper surveys and hydraulic conductivity testing to characterize the fractures and groundwater conditions. It found the most significant, water-conducting fractures near the creek surface and centre, with fracture size and conductivity generally decreasing with depth and distance from the channel.<br /><br />From late 2019 to early 2020, engineers installed a single-row grout curtain across the creek, aligned with the rock bar. They injected a single-part hydrophobic polyurethane grout into boreholes drilled to 17 m depth. The grout was selected to seal water-filled fractures, with its reaction time and spread controlled during injection. Portable equipment and site rehabilitation measures helped limit environmental disturbance.<br /><br />After construction was completed in January 2020, Pool 23 filled following rainfall and began overflowing over the rock bar. Water-level records show the pool has since generally maintained a depth of about 0.8 m above the monitoring sensor. However, monitoring data were unavailable from mid-2017 until remediation began, so the evidence does not provide a continuous record across that period.<br /><br />The case study indicates that investigation-led permeation grouting can restore pool retention and surface flow in a subsidence-affected watercourse. At Pool 23, the approach was reported as technically effective, economically viable and low-impact.

Keywords

longwall mining

groundwater diversion

Myrtle Creek

grout curtain

permeation grouting

hydrophobic polyurethane grout

fracture characterization

pool remediation

surface flow restoration

subsidence impact