Tensile strength of welded Apache Leap tuff: Investigation of scale effects

Brazilian tensile strength of welded Apache Leap tuff was analyzed to investigate the effect of specimen size. Five different nominal diameter specimens were used — the ratio of largest to smallest diameters was about seven. Mean tensile strength is minimum when the specimen diameter is 50 mm. Tensile strength increases somewhat and then becomes independent of specimen size. Significant scatter in tensile strength is observed at each nominal specimen diameter. Evan’s power law did not reproduce the trend of tensile strength variation with specimen diameter adequately. A Weibull plot shows one distinct line belonging to each specimen diameter. By normalizing the measured tensile strength of each specimen by the mean tensile strength of all the specimens having the same nominal diameter, a Weibull plot of the combined data can be fitted by a straight line. Weibull modulus of the rock can be estimated from this plot using the combined data. This plot also indicates the presence of another flaw population especially noticeable in samples with low strength. A scale-dependent conceptual model of flaw population distribution is proposed for explaining the size effect observed.