A sandbox model used to examine the stress distribution around a simulated longwall coal-face

Abstract

A box containing sand is used to examine the possible distribution of stress in the region of coal-mine face workings; the floor of the box represents the top of a coal seam, and strips of the floor can be lowered successively through a distance equivalent to the seam thickness to represent an advancing longwall face. The effects of depth, seam thickness and two types of sand are also considered. In the model, the results show that, as the ‘face’ advances, the weight of the overlying sand is carried by a vault, the larger abutments of which are in the ‘rib-side’ areas (rib-side abutments) with smaller abutments ahead of the ‘face’ (front abutment) and behind the ‘face starting-line’. A minor arch, an abutment of which is in the ‘goaf’ (rear abutment), is thought to span the ‘face’, its span distance being a function of depth and its load a function of seam thickness, sand cohesion and depth. The traditional view postulates a plane strain condition in which the weight is carried by arching from the front to the rear of the face. The relevance of these model results to practical longwall mining conditions is discussed and some evidence is reviewed.