ABSTRACT
Tilt tests have been used in situ and in laboratory as a practical technique to estimate the basic frictional component of rock discontinuities. A number of studies on tilt test results carried out by several authors revealed an unexpected variability of the results. To clear this issue, a statistical approach intended to allow a better understanding of basic friction angle results is presented. Three different parameters potentially affecting the behaviour of a sliding rock slab were considered: base slenderness, tilting rate and saw blade used to cut the slabs. Nearly three hundred tests with different combinations of these parameters were carried out on granite rock slabs. General trends observed for results were analysed by means of a descriptive statistical analysis, histograms and fitted probability distributions. One–way analyses of variance (ANOVA) were performed. Occurrence of abnormal values within datasets was also detected by a thorough assessment of outliers. From this study, it could be concluded that tilt test results may be considered as reproducible values to estimate basic friction angle of rock sliders, since identified variability was within the range of other common geotechnical parameters.
