Characteristics of topographic bedding plane shears inferred from observations and measurements

Bedding plane shears are horizons within rock strata along which horizontal sliding movements occur. They develop as a result of natural processes but can also be remobilised, or even created, by coal mining and other construction activities. Their low strength in shear and lateral persistence have a profound effect on ground movements around extracted longwall panels and give rise to a broad range of phenomena. This paper describes bedding plane shears associated with surface topography using field observations and measurements to explore their characteristic mechanical and hydrogeological properties.

Bedding plane shears form naturally near the surface as a result of the erosional processes that generate surface topography. These features are able to be remobilised by mining to cause valley closure impacts to river channels, enhanced flow paths for groundwater movement and a range of surface impacts. ACARP Project C33015 supported a desktop compilation of four decades of monitoring experience to characterise the nature, mechanical and hydrogeological properties of recognised types of bedding plane shears.

This paper is the second in a series describing the characteristics of different types of bedding plane shears. This paper presents the results of observations of bedding plane shears associated with surface topography. Mills (2024) presents the first in this series; a description of the bedding plane shears that occur close to seam level.