Experimental study on strength and failure characteristics of mortar specimens with prefabricated cracks under uniaxial and triaxial stress

Abstract

Cracks in rock mass have adverse effects on its mechanical characteristics and the stability of rock mass engineering. In this paper, cement mortar is used to make specimens with prefabricated cracks with different dip angles, and uniaxial compression, true triaxial compression and true triaxial unloading tests are carried out. The stress-strain curves under uniaxial compression and true triaxial compression have 4 and 5 stages, respectively. The strength of the specimen is the lowest as the dip angle of the crack is 45 °. Under uniaxial compression, the failure mode is mainly tensile failure, accompanied by a few shear cracks. With the increase of the crack dip angle of the specimen, the types of cracks generated at the tip of the prefabricated crack increase and change from shear crack to tensile crack. The distance between the crack tip and the loading end affects the failure degree of the specimen. Under true triaxial compression, the confining pressure significantly improves the strength and deformation characteristics of the specimen, and weakens the influence of the crack dip angle on the strength. The failure mode as a crack dip angle of 15 ° is mainly tensile, accompanied by tensile-shear composite and shear. The failure mode as crack dip angles of 45 ° and 75 ° is mainly tensile-shear composite, accompanied by tensile failure and shear failure. With the increase of the crack dip angle, the surface spalling of the specimen is more obvious, and the damage degree of the specimen is more severe. Under the triaxial unloading confining, the failure mode is mainly shear, accompanied by tensile and tensile-shear composite, more than two shear cracks through the top and bottom of the specimen lead to the failure. Compared with uniaxial compression, the damage degree of specimen is more severe under true triaxial compression and true triaxial unloading.