Assessing longwall shield–strata interaction using a physical model

Abstract

The stability of the longwall face and shields in thick coal seams requires a thorough understanding of shield–strata interaction, but the realistic hydraulic operations of longwall shields have been widely ignored to date. This paper reproduces the behaviour of the longwall face and shield in response to roof loading through a physical modelling study with a consideration of the basic operating principles of the shield leg cylinder. The extension and retraction of the leg cylinder and important characteristics of longwall shields are introduced. The results show that: (1) the shield vertical stiffness has a positive correlation with shield capacity, and it decreases with the extension of the hydraulic liquid inside the leg cylinder; (2) higher capacity shields develop more load in response to roof convergence, but retain an adequate reserve capacity to protect the shield from damage; (3) yielding of a modern shield represents a 10% drop in yielding pressure and produces 5–10 mm of reduction in shield height and 100–250 t of loss in support load; (4) the physical modelling study of shield–strata interaction with a consideration of leg hydraulic operation shows a step function of roof deflection. Face and roof displace at a slow rate during the initial shield loading stage but increase rapidly during the yielding events.