Strength and fracture behaviors of sandstone samples containing intersect fissures under uniaxial compression

Mechanical behaviors of rocks are significantly influenced by the distribution patterns of fissures. By conduc- ting uniaxial compression tests on sandstone samples containing two prefabricated fractures which interact with each other at the tip,the effects of distribution direction angle (β) and the included angle of intersecting fractures (α) on strength,deformation and fracture evolution properties of sandstone samples were respectively studied. The results show that the peak intensity of samples increases gradually with the increase of angle β,while the average modulus increases first and then turns to decrease. Coalescence failure between the outer tips of pre-existing fractures occurs to rock sam- ples with β of 0°,and when β varies between 30° and 45°,the failure form is characterized by one crack formed at the outer tip of one prefabricated fracture. In the range of β from 60° to 90°,the cracks generated at the outer tips are in- dependent when ultimate failure occurs to rock samples. With the increase of angle β,the crack growth degree at the inner tip of fractures decreases gradually. With the increase of the included angle α,the peak intensity of samples decreases gradually,and the average modulus decreases first,then increases and decreases once again. When α is be- tween 30° and 60°,one crack initiates at the outer tip of one prefabricated fracture,while in the range 90°-150°,two cracks are formed at the outer tips of two fractures respectively. With the increase of the included angle α,the crack growth degree at the inner tip of fractures decreases gradually until no crack initiation. Acoustic emission (AE) char- acteristics were recorded during the loading process by using the acoustic emission equipment,and the results show that AE events mainly occur at peak intensity and nonlinear stage before peak intensity. Pronounced AE occurs when- ever the macroscopic crack generates and propagates.