Face support requirements— A problem in ‘arching’

Abstract Requirements for the load-bearing characteristics of powered supports in British mines have been based upon observations of load/convergence relationships at the face, viewed in the light of a purely geometrical interpretation of the way in which roof strate crumble into the goaf. No analysis of stress conditions at the face has ever been presented. The present report draws attention to the applicability of ‘arching’ theory to the phenomena and applies standard equations to calculate the residual load of unkeyed broken rock which the supports have to carry. This load proves to be closely equal to the value which, in practice, support loads must exceed if excessive convergence is to be avoided. The theory gives support to the current philosophy of support design insofar as loading-bearing capacity is concerned.