MICROSCOPIC MECHANISM OF STRENGTH REDUCTION OF ROCKS

Abstract

Uniaxial compression tests have been conducted on Jinan gabbro at six different axial strain rates ranging from 10~(-8)/s to 10~(-3)/s. Results show that the strength decreases by about 23% with decreasing strain rate. The stress level C_0~' /or the onset of dilatancy is constant for six strain rates. When σ_1C_o~' e_1 and D increase with decreasing strain rate (?) under a specific stress level.Microscopic observations on the stressed rock samples reveal that the density of microcracks for the samples loaded at low strain rates is higher than that at high strain rates; in addition there are also cracks nearly perpendicular to it, which is responsible for the increase of D value.The creep test under the stress σ_(σ_1C_0~') confirms that the growth of microcracks in the rock has been time-dependent effects, and the steady-state creep with (?)=constant developed until the rock fails.Summing up the above reslts shows that when σC_0~', the constitution law of the rockswill be time-dependent, and the C_0~' value is a limit of the rocks strength.