Geomechanical properties of rocks from the rockburst hazard viewpoint

Author: M. Bukowska

Studies carried out over many years by the Central Mining Institute on the geological properties of the Coal Measure rocks in the Upper Silesian Coal Basin have resulted in the acquisition of a substantial data base of mechanical parameters of rocks over the total strain range.

Among the parameters arc the following: peak strength or maximum stress, modulus of elasticity, drop modulus determined from the post-peak range of the stress-strain curve. The post-peak rock properties are closely related with the peak strength and the pre-pcak properties.

Hence, the relationship between the uniaxial compressivc strength Rc, the drop modulus M, and the relationship between the modulus of elasticity E and the drop modulus Mhave been determined. The fundamental mechanical properties of rocks described are needed to predict the "host rock-coal seam" system dynamic failure (rockburst) incidence from the laboratory-based "testing machine platen-rock specimens" system-failure experiment. The paper considers a double roof-seam-floor system, namely, Mcoai Erock (Table 1, variant 1) and A/Coa| Lrock (Table 1, subvariants 2a and 2b) that have been identified through the relationship between Erock and A/Coa|.

A proposed classification of the liability of rocks to rockbursts based on the A/coa|/Lrock index is suggested. A prognosis of the variation of the "host rock-coal scam" system--failurc patterns related to an increase in strain rate has been elaborated, using knowledge of the variation of drop modulus post-peak values obtained for various strain rates, mostly in the 10~4-10"' s~' range.

In the paper, the possibility to use the proposed Mcon\/ETocy index for the analysis of the triaxial compression testing results with regard to the rockburst hazard is suggested.