封圧下における大理石試料の曲げ試験
封圧下における岩石の曲げ破壊に関する研究 (第1報)
1981 年 97 巻 1116 号 p. 83-88
詳細
1981 年 97 巻 1116 号 p. 83-88
Four-point bending tests were undertaken in a triaxial vessel for fine grained and coarse grained AKIYOSHI marbles to reveal the features of bending fracture under confining pressure.
Main results obtained in this study are as follows:(1) When the confining pressure is sufficiently high, the fracture cracks are arrested and, accordingly, the fracture propagation becomes more stable than that under low confining pressure where the rupture takes place immediately after fracture initiation.
(2) The bending moment-outer fiber strain diagram of fine grained marble shows sudden drop of bending moment caused by fracture initiation (Fig. 4 (a)). On the other hand, bending moment in coarse grained marble increases monotonously until rupture (Fig. 4 (b)).
(3) The outer fiber bending stress at fracture initiation increases rapidly with the confining pressure for both fine grained and coarse grained marbles. This suggests that the conventional failure criterion can not predict the outer fiber bending stress at fracture initiation under confining pressure (Fig. 11 (a) and (b)).
(4) Number of fracture cracks initiated between the two loading points increases as the confining pressure increases and decreases as the thickness of the specimen increases (Table 2). On the contrary, average ratio of the length of arrested fracture crack to the thickness of the specimen decreases as the confining pressure increases and also decreases as the thickness of the specimen increases (Table 3).
