Rock specimen and method for testing pure shear of the same

A rock specimen, comprising a rock body having a shape of a cylinder or a regular square prism, the rock body comprising:

• an upper part, an upper end face, a first circular groove, a first cylinder, a first circular body, a lower part, a lower end face, a second circular groove, a second cylinder, and a second circular body;
• wherein
• the upper end face is in parallel with the lower end face;
• the first circular groove is disposed on the upper end face of the rock body and has a circle center coinciding with a center of the upper end face of the rock body;
• the second circular groove is disposed on the lower end face of the rock body and has a circle center coinciding with a center of the lower end face of the rock body;
• a width of the first circular groove is the same as a width of the second circular groove;
• an inner diameter of the first circular groove is the same as an outer diameter of the second circular groove;
• a distance between a bottom of the first circular groove and a bottom of the second circular groove is between 10 and 40 mm;
• the first circular groove divides an upper part of the rock body into the first cylinder located at the center and the first circular body surrounding the first cylinder;
• the second circular groove divides a lower part of the rock body into the second cylinder located at the center and the second circular body surrounding the second cylinder;
• and
• a diameter of the first cylinder is larger than a diameter of the second cylinder.