The authors examine the variability of the distribution of the fracture trace length in some objective districts. Further, we elucidate the influence of the geological factors (the rock type, the age of rock mass and the geological processes of fracturing) on the fractal characteristics (the fractal dimension and the intercept of the fractal distribution).
On ten objective districts dominated by the shear fractures, the fracture trace length was investigated. Four objective districts were governed by the sedimentary rocks (slate, sand stone etc.). Five objective districts were granitic area. Another objective district was covered by andesite. Further, four objective districts investigated to the tension fractures were one dominated by the cooling joints in granite, the other dominated by the cross joints in alternation of sand and mud stone, the other two dominated by the sheeting joints in granitic rocks.
The results are surmmarized as follows:
1) The frequency distribution of the scan grid, in which fractures longer than a certain length l are numbered N, shows the log-normal distribution. The standard deviation δ of log N calculated from the average fractal distribution curve has the range of 0.16 to 0.29.
2) The fractal dimension Dl of fracture trace length is influenced significantly by the geological processes of fracturing, particularly, the difference of the tension and the shear fractures. The tension fractures affected by the geological boundary do not seem to have the fractal property.
3) From the measured data, the fractal dimensions Dg of fracture pattern are 1.5-2.0 regardless of the geological factors.
4) The C-value (the intercept of fractal distribution) for the igneous rock increases with the age of rock mass.
5) The variability of fracture distribution is reduced by the classification of the fractal characteristics because the variability is affected by the multi-fractal property of the fracture system. The measuring method is also another main cause of the variability among the different scales.