Seventeenth Canadian Geotechnical Colloquium: The effect of cohesion loss and stress path on brittle rock strength
Seventeenth Canadian Geotechnical Colloquium: The effect of cohesion loss and stress path on brittle rock strength
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DOI：
10.1139/t97-030
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发表时间：
1997-08
影响因子：
3.6
通讯作者：
C. Martin
中科院分区：
文献类型：
--
作者：
C. Martin
脆性岩石的应力-应变曲线表现出三个特征应力水平：裂纹萌生、长期强度和峰值强度。低围压下的损伤控制试验表明，长期强度和峰值强度对诱导损伤量敏感，即，损伤量越大，长期强度和峰值强度越低。这些试验还表明，脆性破坏过程的特点是随着摩擦力的调动而丧失凝聚力。某圆形试验隧道在大块脆性岩石中的开挖导致了隧道周围的破坏。隧道周围破坏岩石的反算强度约为实验室试验测量强度的一半。当荷载超过无侧限抗压强度的三分之一时，邦纳湖花岗岩在实验室和现场都发生了裂纹损伤。然而，与破坏相关的应力水平是加载路径的函数。在实验室中，加载路径单调增加，无侧限样品的极限强度为225 MPa。数值研究表明，在现场的隧道周围的加载路径是比较复杂的，涉及应力增加和减少和应力旋转。对于这种加载路径，失效在100和120 MPa之间的应力下开始。传统的摩擦破坏准则不能充分预测圆形隧道周围测得的脆性破坏程度。损伤控制的实验室试验和隧道施工过程中进行的微震监测的结果表明，恒定偏应力标准是一个可靠的指标，用于预测损伤的发生。这个标准也被发现给一个合理的预测周围的测试隧道的最大深度的故障。恒定偏应力准则的基本假设是，在低围压条件下，例如在地下开口周围发生的情况下，脆性破坏过程主要由粘聚力损失决定。
Stress-strain curves for brittle rocks show three characteristic stress levels: crack initiation, long-term strength, and peak strength. Damage-controlled testing at low confining stresses has shown that the long-term and peak strengths are sensitive to the amount of induced damage, i.e., the greater the amount of damage, the lower the long-term and peak strengths. These tests also showed that the brittle-failure process is characterized by a loss of cohesion as friction is mobilized. Excavation of a circular test tunnel in massive brittle rock resulted in failure around the tunnel. The back-calculated strength for the failed rock around the tunnel is approximately one-half of that measured in laboratory tests. Crack-induced damage of Lac du Bonnet granite, both in the laboratory and in situ, begins when the load exceeds approximately one-third of the unconfined compressive strength. However, the stress level associated with failure is a function of loading path. In the laboratory, where the loading path monotonically increases, the ultimate strength of an unconfined sample is 225 MPa. Numerical studies suggest that in situ the loading path around the tunnel is more complex, involving stress increase and decrease and stress rotation. For this loading path, failure initiates at a stress between 100 and 120 MPa. Conventional frictional failure criteria did not adequately predict the extent of brittle failure measured around the circular tunnel. The results from the damage-controlled laboratory tests and the microseismic monitoring carried out during tunnel construction indicate a constant-deviatoric-stress criterion is a reliable indicator for predicting the onset of damage. This criterion was also found to give a reasonable prediction for the maximum depth of failure around the test tunnel. The fundamental assumption in the constant-deviatoric-stress criterion is that at low confining stresses, such as those which occur around underground openings, the brittle-failure process is dominated by cohesion loss.