ROCK BRIDGE COALESCENCE MODE OF BASALT-LIKE MATERIALS WITH TWO PRE-EXISTING FLAWS UNDER BIAXIAL CYCLIC COMPRESSION

The initiation, propagation and coalescence mode of flaws in basalt-like materials with two pro-existing flaws are tested under biaxial cyclic compression. The basalt-like materials contain two pre-existing flaws of 30dip, 20mm length, and 0.3mm thickness, varied rock bridge lengths and dip angles. They are molded using similar materials. The results show that:(1)Under biaxial cyclic compression, the failure progress can be divided into wing crack initiation, wing crack propagation and secondary crack initiation, as well as rock bridge coalescence.(2)The coalescence types include shear coalescence, tensile coalescence and shear-tensile compound coalescence. Nine and eight modes can be distinguished particularly using the two experimental methods.(3)In this paper, shear coalescence under biaxial cyclic compression is more possible than that under biaxial compression. Particularly, the crush and uplift phenomenon in rock bridge only exists in biaxial cyclic compression test.(4)Rock bridge coalescence mode is prominently influenced by rock bridge length and dip. With increasing rock bridge dip, the shear coalescence mode and shear-tensile compound coalescence are more undemanding. Under biaxial compression, the shear coalescence mode is predominant accompanied with increasing rock bridge length. However, this pattern is reversed in biaxial cyclic compression test.