Study of the stressed state of a plane during breaking of a barrier between two parallel fractures
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First, on reaching a critical load separation cracks 1 arise in the vicinity of the barrier zone separating fractures at the lower edge of the upper fracture and the upper edge of the lower fracture with α=60° where concentration of tensile stress σ1 is at a maximum.
With an increase in the length of newly formed separation crack 1 there is a reduction in stress concentration close to it and an increase in concentration at the opposite ends of fractures where conditions also arise for the start of growth of cracks 2. After growth of crack 2 the concentration of stress σ1 close to the end of crack 1 again becomes greater than that close to the end of crack 2, giving rise to alternating jumpwise growth of these cracks.
When crack 1 reaches a length of the order ofl1=0.5H it slows down and changes its growth direction inasmuch as there is a change in the direction of tensile stress operation close to its end.
The nature of barrier zone breaking depends on the initial orientation angle of fractures with respect to applied forces.
KeywordsRock Mass Tensile Stress Principal Stress Rock Burst Lower Edge
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