Risk Assessment And Earthworks Management Procedures For Controlled Infilling Of A Disused Quarry Pit

The Eastwood Brickworks is a former shale quarry that operated through most of last century to provide brick making materials that were manufactured on site into bricks. To enable the site to be redeveloped for residential purposes, engineered fill is being placed in the pit that is up to 30 m deep in places. In some parts of the quarry the pit walls were within metres of adjacent residential properties and public roads.

Approximately 1 million cubic metres of fill is required to reach design bulk filling level. Before the start of infilling, extensive sections of the pit walls were near vertical and with some sections undercut by the quarrying activities. A substantial landslide in the high wall of the quarry was a major geotechnical feature that had the potential to remobilise and regress during pit infilling. To enable engineered fill to be placed up to the pit walls, the landslide had to be remediated and the pit walls treated.

This paper discusses the pit wall stability risk assessments and earthworks management practices that have been carried out throughout the project. Detailed geological mapping and geotechnical assessment was carried out at the design stage to assess the risk of instability. Stabilisation measures, monitoring and earthworks methods were developed to manage the risk to workers from slope instability during the filling works that have been underway for over four years. The existing landslide was remediated by earthworks, installation of anchors, drains and batter mesh. Controlled filling up to the pit walls was achieved by a combination of earthworks methods including use of remotely controlled compaction plant, exclusion zones, method specifications for acceptance of fill within exclusion zones and stabilisation measures including scaling and batter mesh.