METHOD FOR DETERMINING MAIN NORMAL STRESS IN ROCK BLOCK Russian patent published in 1996 - IPC

FIELD: ultrasound determination of rock stress state, may be used for finding main stress in blocks. SUBSTANCE: vertical well is drilled from mine working. Average size of elementary structural blocks is determined and elastic wave propagation velocity through the structural elements from well core samples is determined. Minimum distance between wells that is equal to at least seven elementary structural blocks and ten well diameters is determined. Cluster of wells is drilled on apices of right triangle with equal legs. One leg is set as initial zero direction. Time of lengthwise wave propagation between wells and along the wells at equal measurement base is determined. Then trend of action of maximum and minimum normal stresses in three rotational planes are determined. Then a cluster of wells is drilled on apices of a square with sides strictly oriented towards action of the maximum and minimum stress. Time of passing lengthwise waves through inter-well space and along the wells in measured in points of core sampling on the base of measurements equal to cube faces. The above square is admitted as the base. Time of lengthwise wave propagation in rock core samples with core height equal to 1/10 measurement base is measured. Main normal stresses for conditions of volumetric stress state of rock block are determined. EFFECT: higher accuracy. 7 dwg