Search

In this study, triaxial seepage tests on sandstone specimens containing a preexisting fissure were conducted for three different fissure filling states to investigate the effect of fillings on the mechanical characteristics, fracture behaviors and permeability evolution during the seepage stress-induced failure of jointed rocks. Furthermore, the final 3D crack networks were reconstructed using the X-ray CT technique to qualitatively and quantitatively reveal the internal damage characteristics. The results show that the enhancing effect of fillings on the stress thresholds of specimens with a low-dip fissure is greater than that of specimens with a high-dip fissure, especially for the peak strength, while the axial stiffness is more sensitive to the fissure inclination than the filling state. The mud and sand fillings obviously affect the crack initiation angles and change the failure types around the fissure from tension to shear, especially in specimens with a high-dip fissure. Interestingly, the types and initiation locations of the main cracks may change from those observed for unfilled specimens due to the presence of sand fillings. The reconstructed 3D internal failure models show that the crack paths and damage extent inside the specimens are both affected by the fillings and water pressure. Moreover, the permeability evolution is dependent on both the cracking behaviors and fillings. The permeability in the crack incubation stage is more affected by crack propagation than fillings, but the plugging effect of fillings is fully exerted after the crack networks and shear fractures are generated, especially in specimens with a low-dip fissure. [ABSTRACT FROM AUTHOR]

• The creep deformation and failure modes of sandstone with a single fissure are studied. • A new creep model (the damage bond model, DBM) for Particle Flow Code is proposed. • The regularity of crack propagation in the three interpreted creep stages is studied. • The time effect of sandstone failure modes is analyzed with the DBM. As geotechnical engineering expands to deeper formations, the creep behavior of surrounding rock becomes more significant. To better understand the creep deformation and creep propagation of fissured rocks, this study conducts triaxial compression tests and triaxial creep tests of sandstone samples containing a single fissure. The experimental results show that fissured sandstone has a time-dependent failure mode, and creep loading not only causes the crack that dominates the failure of the fissured sandstone to change from a wing crack to an anti-wing crack but also produces more secondary cracks, which are obvious in samples with a low-angle fissure. The steady-creep rate of fissured samples is higher than that of intact samples and first increases and then decreases with increasing fissure angle. The sample with a 45° fissure produces the maximum axial deformation before entering the accelerated creep stage. The theory of the damage bond model (DBM) applied in Particle Flow Code software is proposed, combining the Kachanov damage theory and linear parallel bond model. The DBM effectively simulates the creep deformation and crack propagation process of sandstone in all creep stages, and the failure mode is consistent with the test results. During the initial and steady-state creep stages, the number of microcracks slowly increases, generating a dispersed distribution that rarely exhibits coalescence. Then, the microcracks propagate unstably and coalesce macroscopic cracks, and the accelerated creep stage starts, which is both stress- and time-dependent. Under the same deviatoric stress, the creep simulation samples generate more microcracks than the triaxial compression samples and exhibit a greater reduction in the width of the preexisting fissure after failure. Creep damage accumulation with time significantly affects the evolution of contact forces and displacement vectors. A stress concentration is more likely to occur along the propagation path of an anti-wing crack in creep samples, and the anti-wing cracks present a trend of shear failure. This study plays an important role in predicting the deformation of fissured surrounding rock in underground engineering and explaining the mechanisms of catastrophic events due to the evolution of damage. [ABSTRACT FROM AUTHOR]

A correction to this paper has been published: https://doi.org/10.1007/s10064-021-02296-1 [ABSTRACT FROM AUTHOR]