Most of the roadway excavation is completed by the drilling and blasting method. With the increase of buried depth, the existence of ground stress will generate a significant impact on the rock blasting, especially on the smooth blasting. In this study, self-made homogeneous similar materials and digital image correlation methods were used to determine influence of ground stress on the smooth blasting under uniform explosive charge parameters and various in situ stress conditions. The results show that the crack outline after blasting changes from zigzag to straight in shape, and multifractal calculation results of the rupture section between blastholes show that the fracture surface becomes flatter as ground stress increases, which is conducive to roadway formation. The strain and equivalent strain rate obviously decrease as the distance between the blasthole and measuring points increases. The same trend occurs as the confining pressure goes up. Meanwhile, a postexplosion acoustic wave test indicates that confining pressure inhibits damage of the retained rock, which is consistent with strain and equivalent strain rate results. Finally, we discussed the crack propagation mechanism of rock in smooth blasting.
An efficient finite element (FE) method, multivariate quadratic regression approach, is
proposed for calculating the fatigue stress spectrum of engineering structures. The calculation starts
from a dynamic load history. A regression function is established as a relation from the concurrent
components of structural balance force systems into the structural stress. Parameters of the relation
are measured by the stress data using an elastic-plastic FE method under selected groups of balance
force systems. The selected systems should cover the possible load range with a similar service
condition. After passing the fit effect check, the regression equation can transfer the structural load
history into the stress history at the preferred position. Application on the determination of fatigue
stress spectrum for the bolster of K6 type bogie has indicated availability of the present approach.
Some deficiencies have been overcome from the much time cost by transient approach and the entire
elastic material relation by quasi-static approach.
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