Cracks and fissures contained in rock masses influence remarkably their own strength or drillability. Fissures have a primary influence on mechanical and elastic properties of rock. Such interrelation can be represented by the following empirical equation.
n= 5.0/ (k+m) 2-4.0
Where,
n: the frequency of fissures defined as the number of fissures per unit length (meter).
k=υ/V (υ: the velocity of P-wave propagated in rock masses, V: the velocity of P-wave propagated in rock specimen)
This ratio k gives the index to degree of fissuring.
m: coefficient of uniformity, which depends on degree of weathering, porosity and strength.
The strength of fissured rock masses Sf can be estimated as
Sf=k2Ss
if the strength of non-fissured rock specimen Ss and the index to degree of fissuring k are assumed.
