Abstract
Excavation and unloading operations in underground rock engineering can cause strong disturbances to the original in situ stress, potentially leading to disasters such as spalling and rockburst. To address the inadequacy of strength analysis research, this study employs the energy analysis method. By analysing the relationship between different confining pressure unloading paths, a series of constant deviatoric stress direct and cyclic unloading triaxial tests were conducted to obtain the energy evolution process. Based on this, the energy evolution mechanism of the unloading confining pressure test path was revealed, and the influence of this path on the brittleness of the specimen was discussed. The research results indicate that confining pressure unloading leads to active energy release, triggering energy imbalance release and energy transfer mechanisms, which generate tensile and shear fractures, respectively, leading to energy dissipation. Throughout the entire test process, energy dissipation mainly comes from the elastic energy stored in the specimen before the unloading point, while the external work is relatively small. The elastic energy ratio continuously decreases from the unloading point. In addition, different triaxial confining pressure unloading tests can be regarded as the coupling of two stress path mechanisms: when the stress deviation remains unchanged, the spherical stress decreases, and when the stress deviation changes, the spherical stress remains unchanged. Furthermore, tensile microcracks weaken the brittleness before the peak and enhance it after the peak. The research results can guide the construction schemes of rock underground engineering.
Highlights
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The unloading of confining pressure leads to the active release of energy, triggering energy imbalance release and energy transfer mechanisms, which generate tensile and shear fractures, respectively.
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During the unloading of confining pressure, the dissipation of energy primarily originates from the elastic energy stored in the specimen before the unloading point, with less contribution from external work.
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Different triaxial unloading tests can be considered as the coupling of three energy mechanisms, namely energy saturation, energy imbalance release, and energy transfer mechanism.
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The tensile microcracks generated during the unloading process of the specimen have weakened the brittleness before the peak and enhanced it after the peak.
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Data availability
Some or all data, models, or codes that support the fndings of this study are available from the corresponding author (hliucumt@163.com) upon reasonable request.
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The financial and general supports for this research provided by the National Key Research and Development Plan (Nos. 2016YFC0501103) and the National Natural Science Foundation of China (Nos. 51804298).
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Li, Y., Han, L. & Shang, T. Energy Evolution and Brittleness Analysis of Sandstone Under Confining Pressure Unloading. Rock Mech Rock Eng (2024). https://doi.org/10.1007/s00603-024-03818-5
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DOI: https://doi.org/10.1007/s00603-024-03818-5