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Abstract Cracks in rock will initiate，propagate and coalesce under loading，which remarkably influences the strength and damage property of rock. Based on a DIC system which was proved reliable，uniaxial compression experiments were carried out on the specimens with two precast flaws. The strain field and strain localization of the whole specimen were obtained. It was found that the strain localization and the progressive damage were very distinctive in the test. The strain localization zone appeared in the initial phase governed the range and trend of the whole process of the strain field development. There were four failure modes found in the test，that is the non-coalescence mode，the coalescence mode at inner tip of flaws，the coalescence mode at outer tip of fracture and the inner-outer tip coalescence mode. The bridge angle and the arrangements of flaws had the effect on the formation of strain localization zone in mesoscopic level and determined the cracking path and the failure mode in macroscopic level. The coalescence of strain localization zone in the bridge area resulted in a fluctuation of stress-strain curve before the peak and reduced the peak strength. The slower the coalescence of the strain localization zones，the higher the peak strength.
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2015, Vol. 34 
