The process of weathering alters and usually weakens coal-bearing rocks. It is typically restricted to the surface layers. However, deep weathering can occur in permeable lithologies and along fractures as the result of oxidizing conditions, usually brought on by water percolation. The weathered strata most often are stained yellow to brown, the result of iron in the ferric state. The depth of weathering depends on many factors, the most important being rock type and climatic conditions. Weathered materials are weaker than fresh parent material.
In surface mines, weathered overburden is usually easier to strip (Pictures 1 and 2). However, because it is inherently weak, the weathered overburden is sometimes prone to highwall failure. Weak mechanical properties, decreased even further by meteoric water saturation, can promote slope failure (Picture 3). Weathered material usually does not provide a suitable base for a spoil pile. Because of its reduced mechanical strength, it could produce a weak plane for potential spoil pile failure.
Figures & Tables
This volume of the “Atlas of Coal Geology” provides 393 images on various subject matters related to coal deposits and coal resource utilization. The supporting text provides an introductory overview of coal exploration, mining, and coalbed methane (CBM) development, followed by discussions on various megascopic aspects of coal geology (microscopic aspects are covered in Volume 2). Because of the vast subject matter, many generalities had to be made in the text. References are included to guide those interested to more detailed discussions. All citations within the document are linked to the detailed reference list for this volume. The overriding theme for this publication is that a picture is worth a thousand words.