Summary

In the paper the attention was paid to the dangerous spalling of rocks from working sides and pillars. The application of the horizontal bolting in the mines of LGOM and of Olkusz was successful. The laboratory in- vestigations of horizontally bolted concrete cylinders showed the increase of the compression resistance equal 15 %. The calculation of the horizontal bolting based on Cymbarewicz theory resulted in the high lenght of bolts. As the spalling occurs along the parabola we may apply the known formula of Protodiakonow for calculation of the bolting parameters.

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