58 research outputs found
Integrating borehole-breakout dimensions, strength criteria, and leak-off test results, to constrain the state of stress across the Chelungpu Fault, Taiwan
No full textTrue triaxial failure characteristics in rocks from granite to sandstone: experimental results and theoretical predictions – a review
Full text linkMogi’s (1971) seminal article on a new testing machine for conducting true triaxial experiments in rock included the first set of test results showing that failure (in the form of s1, peak) is a function of not only s3, but also of s2. However, Mogi’s pioneering work went seemingly unnoticed by the rock mechanics community. Some 30 years later, Haimson and colleagues (2000–2014) fabricated a similar loading system and employed it to determine true triaxial deformability and failure criteria in several crystalline and clastic rocks. The most important discovery enabled by true triaxial measurements was the effect of the intermediate principal stress s2, for given s3, on failure level s1, peak (it is at its lowest when s2 = s3), on fault-normal direction (always aligned with that of s3), on fault angle ? (? rises, as s2 increases, by up to 20° in crystalline rocks and up to 10° in clastics), and on deformability (the onset of dilatancy rises with s2). Haimson and Rudnicki (2010) complemented true triaxial experimental data on TCDP siltstone with results of shear band localization theory applied to fault angles observed for axisymmetric compression (Lode angle T = +30°) and deviatoric pure shear (T = 0°), to infer properties of the inelastic constitutive behavior. They employed these properties to predict ? for other Lode angles used during the experiments, yielding acceptable agreement with actual observations. The results were used to predict the angle variation for constant mean normal stress with increase in Lode angle, and for constant Lode angle with increasing mean normal stress. More recently, Ma et al. (2014) reported true triaxial experimental results in porous sandstones in which failure stress conditions and failure-plane angles were recorded and analyzed. The observed effect of s2 on both s1, peak and failure-plane angles was compared with Rudnicki (2013) theory. It was found that the theoretical predictions of failure-related s1, peak for given s3 replicated reasonably well actual test data, except for the two extreme magnitudes of s2, where predictions underestimated experimental data. With respect to failure-plane angles, Rudnicki’s theoretical prediction replicated the general rise of the experimentally observed ? with s2 for a given s3, as well as the diminished rise at high s3 magnitudes. The reasonable qualitative agreement between the predicted and the observed failure-plane angles demonstrated not only the applicability, but also the limitations of Rudnicki’s (2013) theory
Failure of two porous sandstones under true triaxial conditions
Full text linkThe role of the intermediate principal stress in rock failure has been a subject of continuing debate since the pioneering work of Mogi in the 1960s with true triaxial tests. These are tests in which all three principal stresses are different, ,, positive in compression. In recent years, an increase in data from such tests, some at constant Lode angle and/or constant mean stress, has provided additional fodder for discussion. Here, we analyze the results of tests on true triaxial data from two porous sandstones, Coconino [1] and Bentheim [2]. The tests are of two types: conventional tests which are fixed and are increased to failure; and novel tests which are fixed and are increased so that the ratio has fixed values: 0, 1/6, 1/3, 1/2, and 1, corresponding to Lode angles of and . The analysis is based on a modified form of the Matsuoka–Nakai/Lade–Duncan condition, employed earlier by Haimson and Rudnicki [3] for the prediction of fault angle: where . is determined by the mean stress dependence in deviatoric pure shear ( ). controls the shape of the failure surface in deviatoric planes: For the shape is circular, as for a Drucker-Prager material; for , the shape is triangular, as for a Rankine material. Dependence of on allows changes of shape of the failure surface with mean stress. For both sandstones, data for are well-fit by a quadratic function for . Data for the Coconino are consistent with a positive slope for whereas those for the Bentheim sandstone suggest a peak in the curve. The dependence of on is determined from the values calculated for . For both sandstones is approximated by a bi-linear function of . For the Coconino remains positive in the range of the data but for the Bentheim becomes negative for greater than about 180 MPa. This feature appears to be related to the peak in the curve. Curves calculated for at other values of fit the data well. These forms for and are used with the above criterion to calculate results for conventional true triaxial tests and compare with observations. The calculated results exhibit the typical behavior that at failure for fixed increases to a peak and then decreases with increasing . Agreement with the data is generally good, although less so for axisymmetric stress states. REFERENCES [1] Ma, Haimson, Abstract T33C-2435, 2011 Fall Meeting, AGU, San Francisco, California, 2011. [2] Ma, Rudnicki, Haimson, Geophysical Research Abstracts, Vol. 16, EGU2014-1800-1, 2014. [3] Haimson, Rudnicki, Journal of Structural Geology, 2010
Consistent trends in the true triaxial strength and deformability of cores extracted from ICDP deep scientific holes on three continents
No full textMechanical characterization of pink lac du Bonnet granite: Evidence of nonlinearity and anisotropy
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Aspects of Mechanical Behavior of Rock under Static and Cyclic Loading. Part B. Mechanical Behavior of Rock under Cyclic Loading
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