Fig. 5A shows the mean spacings for the granodiorites and quartz monzonites in the
five weathering grades and summary statistics are given in Table 2. Although relationships
between medians were analyzed, these data are not shown. Mean spacing increases very
slightly from fresh and slightly weathered rock, then decreases to moderately weathered
rock. Mean spacings then become increasingly wider from moderately weathered through
highly and completely weathered rock. The decrease in mean joint spacing in moderately
weathered rock was expected (see Fig. 2D).
Mean spacings for each weathering grade in the Asian granites are shown in Fig. 5B
and the data are given in Table 2. Again, medians are not shown. The widest spacings
occur in fresh granites. Mean spacings decrease from fresh to moderately weathered rock,
and then become wider in highly and completely weathered granite so that spacings in
completely weathered granite are almost as wide as those in fresh granite. Joint spacing
relations for these granites were previously reported in Ehlen (1999). The decrease in
mean joint spacing between fresh and slightly weathered granite is exhibited by this data
set, but not by the data from the southwestern United States, at first appears inexplicable.
However, the majority of measurements in fresh rock were made in a very poorly lit tunnel (the brightest light was a headlamp). Thus, it is possible that many smaller joints were
simply not visible. In addition, this tunnel was formed by blasting and, while every effort
was made to avoid fractures formed by blasting, it is possible that there may have been
confusion between natural fractures and those formed by blasting.
If the spacings for the two data sets are combined, the pattern becomes more distinct as
shown in Fig. 6A. Summary statistics for the combined data sets are given in Table 2. Mean joint spacings decrease from fresh to moderately weathered rock, reaching a maximum in
moderately weathered rock, then increase from moderately weathered rock to completely
weathered rock. Mean spacings are widest in completely weathered rock. An analysis of
variance shows a statistically significant difference between the mean spacings for the five
weathering grades at the 95% confidence level. The F-ratio is 23.00 and the P-value for the F-test is less than 0.05. The Kruskal–Wallis test also shows that there is a statistically
significant difference among the medians for joint spacing among the five weathering
grades at the 95% confidence level.