Stress in the solid rock during firing of charges with oval cross section
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When oval-sectioned charges are fired, the stresses produced in the solid rock are distributed nonuniformly, the nonuniformity increasing markedly with increasing ratio of the semiaxes of the ellipse.
The maximum tensile stresses produced by firing oval charges are greater than for circular charges, both near the powder chamber and at a considerable distance.
Near the powder chamber, the maximum tensile stresses appear at points on the major axis projected (with θ=0°); with increasing distance from the chamber these points are displaced, somewhat towards points on the minor axis projected.
Near the powder chamber the maximum tangential stresses also appear at points on the major axis projected (with θ=0°), but with increasing distance from the chamber the maximum is rapidly displaced towards points on the minor semiaxis projected (θ=90°)
Since nonuniformity of stress distribution is a very important factor in the fracture of rocks under dynamic loads, and since the maximum tensile stresses appear at the same distance from the powder chamber, we should expect a greater volume of fracturing from oval charges than from circular charges of equal weight. Experiments by the authors of [1, 2] have shown that the volume of rock fractured by oval charges increases with the ratio of the length of the charge to its cross-sectional width.
KeywordsElasticity Theory Hard Rock Maximum Tensile Stress Solid Rock Maximum Tangential Stress
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