A study of tunnel stability and barrier pillar design in mines of the Cape Breton coalfield.

摘要

Aspects of stability of access tunnels with particular reference to the factors controlling face access tunnel closure upon the efficiency of coal production and safety of longwall mining operations are investigated. These are used to justify the present studies of tunnel stability and barrier pillar design in mines of the Cape Breton Coalfield.; An analysis of in situ deformation data of 26 face access tunnels by tunnel convergence measurement and a new photographic technique for approximately 40 km of tunnels are presented. Comparative studies of these techniques are made and deformation characteristics with respect to depth of cover, panel width, extracted seam height, barrier pillar width, type of steel arch supports and the effect of adjacent workings are investigated.; Due to the narrow range of field data, the effect of such parameters as extracted seam height, panel width, tunnel shape and tunnel size could not be examined, nor could the influence which the material properties may have on tunnel closure be identified. Hence, comprehensive parametric studies by two dimensional finite element simulation of the face access tunnels by use of MSAP2D are undertaken. Stress and displacement distributions and the extent of any failed zone around the tunnel with respect to the aforementioned parameters together with barrier pillar width, and the stiffness of the surrounding materials are considered.; The existing theories for tunnel convergence prediction are described. From this investigation it is found that some of these theories are inapplicable to soft rocks at depth. Those which are applicable, due to their limitations, are not suited for prediction of the vertical convergence profile from tunnel faceline in longwall coal mining. Hence, a new theoretical exponential formula for tunnel convergence prediction based on a modified Mohr-Coulomb failure criterion is developed and checked against in situ convergence measurements.; The current barrier pillar design criteria are also investigated. It is found that these criteria yield too conservative a design and are not suited for depths greater than 600 m below ground surface. Hence, two theoretical methods of designing barrier pillar width for longwall coal mining are developed and compared with field data and current barrier pillar design criteria.