Model study of fracture around underground excavations in weak rocks

The paper discusses the fracture pattern around single and twin openings in weak materials of sand/wax and sand, wax/plaster of paris mixtures under controlled loading conditions.The fracture pattern observed on these models suggest that the failure is mostly as a result of stress concentration around the crown of the opening followed by the extension of zones of high stress concentrations in the abutments.The study of fracture characteristics and load-deformation behaviour suggest that from the stability point of view, more stable conditions are obtained when the openings are one above the other and are parallel to the direction of loading in a given ground conditions.