Measurement of type-1 and type-H fracture toughness for rocks and its influence factors analysis

Key words:  rock  test piece  fracture toughness  hydraulic fracture

Abstract:

Based on the principle of cdculating the stress intensity factor of SNBD test piece, a fracture toughness test system for type-I and type-0 rocks was designed. The fracture toughness of type-I and type-U rocks was tested，and the results were compared with the results of type-I fracture toughness tested by thick-walled cylinder. According to the experimental data, the effects of sample size, confining pressure and other factors on the fracture toughness of type-I and type-11 rocks were analyzed- The results show that the fracture toughness of type-I and type-H rocks can be tested by this experimental device with higher accuracy. The sample thickness is greater than 30 mm, and the fracture toughness of type-1 and type-fl rocks can be determinwl when the ratio of initial fracture half-length to disc radius( a/R) ranges from (XI to 0. 3, The fracture toughness valuer of type-I and type-H rocks increase with the confinitig pressure increasing.