Μulti-jointed stratified hard rock roof analysis and design

An arched roof can support a much greater load than a horizontal beam. This increase in the carrying capacity stems from the fact that the downward movement due to gravity creates a compressive arch. The behavior of multi-jointed hard rock roof under gravity load is hereby investigated under the novel view of the compressive arch forming a catenary curve. Analytical formulae are derived, that evaluate, for any given geometry, the loading and mechanical parameters of the multi-jointed roof and its deflection and strain, in terms of the extreme and mean arch thickness. Relations between the applied load, opening and sag are provided for the three basic modes of failure: buckling, crushing and slip. These relations are validated in two ways; though experimental data and by comparison to a real case of an underground magnesite mine. Roof support design to prevent the above modes of failure is provided.