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Optimization of impact bit spacing using ultrasonic wave transit time measurements.

lnyang HI; Pitt JM
Rock mechanics: contributions and challenges: proceedings of the 31st U.S. Symposium, June 18-20, 1990, Colorado School of Mines, Golden, Colorado. Hustrulid WA, Johnson GA, eds. Brookfield, VT: A.A. Balkema, 1990 Jan; :519-526
For rock excavation equipment that applies impulse loads, bit spacing is one of the important determinants of rock fragmentation efficiency. If impact bits are too closely spaced, fractured zones around impact points may overlap excessively, resulting in the removal of tiny rock fragments. Consequently, the ratio of the energy expenditure to volume excavated, termed the specific energy, will be high. High specific energy implies that the efficiency of the excavation process is low. If the impact bits or points are too widely spaced, the fractured zones may exist in isolation and the beneficial effects of pre-fracture may be restricted only to those zones. For the latter case, considerable energy would still be expended in rock cutting. To improve cutting efficiency, impact bit spacing should be selected such that fractured zones overlap minimally. A non-destructive testing technique for estimating the size of fractured zones around impact points in hard rocks was developed. Using a special impact hammer designed for this investigation, cubic blocks (length = 22 cm, width = 22 cm and height = 20 cm) of Academy Black Granite and Lac Du Bonnet Granite were loaded by impact. A James V-meter ultrasonic tester was used to monitor fractures resulting from impact loads. The objective was to measure the sizes of the fractured zones and hence, determine the optimum bit spacing for machines that excavate in rock. A scheme for incorporating obtained laboratory test results into the design of booms for rock excavation equipment is presented.
Rock-mechanics; Geology; Excavation-equipment; Ground-stability; Elastic-properties; Wave-propagation; Crack-propagation; Cutting-tools; Ground-control; Structural-analysis; Ultrasonics; Underground-mining; Mining-equipment; Mining-industry; Coal-mining; Compression-tests; Vibration; Vibration-effects
Publication Date
Document Type
Conference/Symposia Proceedings
Hustrulid WA; Johnson GA
Funding Type
Fiscal Year
Identifying No.
Grant-Number-G1164119; Grant-Number-G1174119; Grant-Number-G1184119
Source Name
Rock mechanics: contributions and challenges: proceedings of the 31st U.S. Symposium, June 18-20, 1990, Colorado School of Mines, Golden, Colorado
Page last reviewed: September 2, 2020
Content source: National Institute for Occupational Safety and Health Education and Information Division