Post-Peak Stress–Strain Curves of Brittle Hard Rocks Under Different Loading Environment System Stiffness

• Published in: Rock mechanics and rock engineering 2022-07, Vol.55 (7), p.3837-3857
• Main Authors: Hou, P. Y., Cai, M.
• Format: Article
• Language: English
• Subjects: Axial strain; Axial stress; Brittleness; Civil Engineering; Compression; Control systems; Deformation; Design engineering; Distribution; Earth and Environmental Science; Earth Sciences; Energy absorption; Failure modes; Geophysics/Geodesy; Modulus of deformation; Original Paper; Rock; Rocks; Servocontrol; Slope; Slopes; Stiffness; Strain; Strain rate; Stress-strain curves; Stress-strain relations; Unloading
• ISSN: 0723-2632; 1434-453X
• DOI: 10.1007/s00603-022-02839-2

To systematically study the influence of loading environment system stiffness ( LESS ) on post-peak stress–strain curves and failure modes of brittle hard rocks, marble and granite specimens are tested under uniaxial compression under axial-strain-controlled loading using a brittle hard rock testing system named Stiffman with variable LESS . The test results show that the post-peak descending slopes of the stress–strain curves under low LESS are steep, and with the increase of the LESS , the slopes are gentle. In addition, as LESS increases, AE events in the post-peak deformation stage gradually transit from a concentrated distribution near the peak strength to a dispersed distribution in the whole post-peak deformation stage, and the maximum AE rate and the maximum cumulative AE count decrease approximately linearly with the increase of LESS . The number of splitting macrocracks and the degree of damage decrease as LESS increases, indicating that the post-peak failure process is more stable when LESS is high. The mechanism that leads to different post-peak descending slopes of stress–strain curves under different LESS is analyzed by comparing the variations of axial stress, axial and lateral strains, rates of axial and lateral strains over time in the loading process, and analyzing the relations between the maximum axial stress drop rate, the average axial strain rate amplitude, the maximum lateral strain rate and LESS . Fitting formulas relating LESS to the post-peak deformation modulus are established. Finally, pillar stability is discussed based on energy absorption and release considering the post-peak slopes of the pillar and surrounding rock. Considering the influence of LESS on the post-peak stress–strain curves of rocks, it is advisable to obtain strength and deformation properties of brittle rocks in line with the field LESS so as to provide more accurate parameters for rock engineering design and analysis. Highlights Influence of loading environment system stiffness ( LESS ) on post-peak deformation of rock is studied experimentally. LESS affects the amount of loading/unloading adjustment by the servo-control system. Rock dilation is reduced with the increase of LESS , which will result in smaller unloading adjustments. As LESS increases, the post-peak stress–strain curve becomes flatter.