Stresses around Openings in Bedded Rock

Distribution of stresses about rectangular openings excavated in bedded rock was investigated by means of photoelastic experiments using 37 kinds of models made of gelatine jelly. By those model experiments, influence of ratio of the breadth to the height of the opening, thickness and elastic modulus of immediate roof and high roof, thickness of packs in the goaf, and fissures contained in the immediate roof or the high roof on the distribution of stresses around the opening was studied. Influence of the thickness of immediate roof, height of caved rocks in the goaf or rigidity of face props in long wall working face were investigated as well. As the results of those experiments, following conclusions were obtained : 1. The tensile stresses of the roof in the bedded rock are larger than these stresses which arise in the non-bedded rock, and the tensile stresses on the roof are larger than the tensile stresses on the floor. 2. When the immediate roof is thick, the tensile stresses on the roof and the compressive stresses on the side walls are considerably smaller than those stresses which arise when the immediate roof is thin. 3. When the high roof is thick, the tensile stresses on the roof are still more small, and the compressive stresses on the side walls are a little larger than these stresses which arise when the high roof is thin. 4. When the modulus of elasticity of the immediate roof is large, the tensile stresses on the roof are larger and the compressive stresses on the side walls are smaller than these stresses which arise when the modulus of elastisity of the immediate roof is large. 5. The compressive stresses on the face decrease as the thickness of the packs in the goaf increases. However, the magnitudes of tensile stresses on the roof undergo only little change. 6. When the immediate roof is fissured, tensile stresses on the roof are almost equal to zero. 7. When the high roof is fissured, the tensile stresses are larger as compared with the case in which the high roof is not fissured. 8. The compressive stresses on the long wall face decrease as the height of caved rocks in the goaf increases. 9. The compressive stresses on the face decrease as the rigidity of face props increases.