The Size Effect and Experimental Error of the Strength of Rocks

Abstract

The dispersion of the measured value of the strength of rock consists of its “inherent” dispersion and the experimental error. the former is caused by the statistical distribution of the socalled Griffith cracks, and the latter can be accompanied with any kind of the measurement. in order to estimate the amount of the “inherent” dispersion, the uniaxial compressive and tensile strength of various sizes of the test piece are to be measured, and Weibull's coefficient of the uniformity is to be estimated. Using the estimated value of Weibull's coefficient of the uniformity, the value of the “inherent” dispersion and the experimental error is to be calculated. from the observation and culculation, it is concluded as follows; (1) the value of Weibull's coefficient of the uniformity of the uniaxial compressive strength does not differ much from that of the uniaxial tensile strength, as suggested by the theoretical consideration. (2) in the standerd testing method of the strength of rock in the present days, the experimental error up to several percents can not be avoided. (3) the accuracy of the uniaxial tension test is less inferior than that of the uniaxial compression test. © 1969, The Society of Materials Science, Japan. All rights reserved.