7.3.4 Results of regression analyses
The equations and correlation coefficients obtained from the plots are
given in Table 3. An exponential function is adopted to fit the
variation in mass results:
m=1-aex/t (1)
where m is the mass variation in different cycles; a and t are
constants; x is the experimental period.
Meanwhile, a power function is adopted to fit the variations in surface
hardness and P-wave velocity results:
H (Vp) =1-axc (2)
where H (Vp) is the variation in surface hardness (P-wave velocity) in
different cycles; a and c are constants; x is the experimental period.
The correlation coefficients for mass, surface hardness and P-wave
velocity versus the cycles of three experiments range between 0.95 and
0.98, suggesting that they can capture the changes of these parameters.
All these results are basically consistent with Fang et al. (2015) and
Ă–zbek (2014).
The variation in mass is only applicable to the sandstone weathering
rate with cracks or flaking. The surface hardness and P-wave velocity of
each sample gradually decrease with increasing cycles, which can be
considered as the acceleration of sandstone weathering rate. It is thus
limited to evaluate the weathering rate by calculating the variation in
mass of sandstone, and the variation in surface hardness and P-wave
velocity can be properly established to test the approximate value of
the weathering rate (Li, Wang, & Chikaosa, 2008). The approximate value
of sandstone weathering rate can be established using the following
formula:
V = 1-A XC (C>0) (3)
where V is the approximate value of the weathering rate; A is
the coefficient of weathering
decline, i.e., the higher the coefficient of weathering decline is, the
faster the weathering rate is; X is the weathering period; and C is a
constant.