Aimed at the characteristic of discreteness of the coal sample

pulse-penetrating method is used to measure the acoustic wave speed and the strength test is finished on MTS815.03 servo-controlled rock mechanical test system. The relationship between acoustic wave velocity and mechanical parameters is obtained through regression analysis. This provides one technical method which can eliminate blind test to a great extent because of the discreteness of rock strength. On this basis

the triaxial compressive test of coal sample is done using MTS815 servo-controlled rock mechanical test system. The results indicate that it is different from the high strength rock such as granite because of the existence of micro holes and cracks in coal. Under the confining pressure

the holes and cracks are compressed and closed; and the elastic modulus increases with the increasing of confining pressure

but it is not linear relative. Additionally

the conclusion that the triaxial strength and residual strength of coal increase with the confining pressure can be used to guide the research on the bolting mechanism of those roadways which are drived in cracked coal mass.