封圧下における岩石のコンパクトシェア試験
岩石のせん断破壊過程に関する研究 (第2報)
1985 年 101 巻 1164 号 p. 49-54
詳細
1985 年 101 巻 1164 号 p. 49-54
In the previous paper, the authors proposed the method, so-called compact shear test, for determining ModeII fracture toughness of rocks.
In this study, the compact shear tests are conducted under confining pressure in order to evaluate theeffect of confining pressure on the Mode II fracture toughness for six kinds of rocks, i. e., Kimachi sandstone, Ogino tuff, Emochi welded tuff, Inada granite, Akiyoshi marble and Tohoku marble. The specimen is 110mm wide, 60mm high and 30mm thickwith two 20mm pre-cracks as shown in Fig. 1.
KIIC of the various rocks are found to increase with confining pressure. For example, the ratios of KIIC under the confining pressure of 240kg/cm2 to that under atmosphere are 3.4 for Kimachi sandstone, 4.1 for Ogino tuff, 2.3 forboth Emochi welded tuff and Inada granite, 2.8 for Akiyoshi marble, and 2.5 for Tohoku marble. For each confiningpressure, a consistent relationship is found between secant Young's moduli and KIIC of the rocks employed as shown in Fig. 8.
Although the ratio of Mode II fracture toughness obtained in this study to Mode I fracture toughnessevaluated with the splitting testing method is about 1.1 at atmospheric pressure, this ratio (KIIC/KIC) increases more orless with confining pressure for four examined rocks as shown in Fig. 9. This shows that Mode II fracture toughness is more affected bythe confining pressure than Mode I fracture toughness.
