Experimental Study on Comprehensive Real-Time Methods to Determine Geological Condition of Rock Mass along the Boreholes while Drilling in Underground Coal Mines
Table 4
Rock mass classification based on the spectrum energy distribution.
Rock mass classification
Frequency range
0–400 Hz
400–800 Hz
800–1600 Hz
I
High energy distributes in the entire frequency range
High energy distributes in the entire frequency range
High energy distributes in the entire frequency range
II
Energy is weaker than Class I and mainly distributes within 250–350 Hz
Energy is weaker than Class I and mainly distributes within 500–700 Hz
Energy is weaker than Class I and mainly distributes within 1100–1300 Hz
III
Energy is weak and mainly distributes within 0–200 Hz
There is no obvious spectrum distribution
Energy is weak and mainly distributes within 1200–1600 Hz
IV
Energy is weak and mainly distributes within 0–200 Hz
