Abstract
To study the fracture propagation and meso damage evolution law of saturated sandstone under unloading (unloading confining pressure), three unloading confining pressure tests of sandstone under different initial axial pressures were designed. By means of nuclear magnetic resonance (NMR) technology, the variation characteristics of rock porosity and T2 spectrum curves were analyzed, the relationship between damage degree and unloading confining pressure ratio was established, and the fractal characteristics of NMR were analyzed. The results show that: (1) The larger the initial axial compression, the larger the axial strain and the smaller the radial strain when unloading failure occurs. With the increase of unloading confining pressure ratio, the elastic modulus decreases, and the Poisson’s ratio and strain increase. (2) T2 spectrum peak shows that the pore size increases with the increase of unloading confining pressure ratio. The larger the initial axial compression, the larger the pore size. (3) Porosity increases exponentially with the increase of unloading confining pressure ratio, in which the number of micropores continues to increase, the number of mesopores and macropores first decreases and then increases. The initial axial pressure promotes the development and expansion of pores. (4) The relationship between pore characteristics, energy and damage degree is generally consistent, and the fractal characteristics of three sizes of pores show different changing rules with the increase of unloading confining pressure ratio.
Highlights
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With the increase of unloading confining pressure ratio, the rock gradually changes from elastic deformation to plastic deformation.
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The failure of the sample is caused by the sharp increase of the number and size of pores.
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Porosity increases exponentially with the increase of unloading confining pressure ratio.
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With the increase of unloading confining pressure ratio, the number of micropores continues to increase, and the number of mesopores and macropores first decreases and then increases.
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Data availability
The data that support the findings of this study are available on request from the corresponding author.
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Acknowledgements
This experimental work was financially supported by the National Key Research and Development Program of China (2022YFC2905003), the National Natural Science Foundation of China (Grant No. 52274109), the National Natural Science Foundation of China (Grant No. 51974012), and the Postdoctoral Science Foundation of China (2021M690361) for financial support.
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JF funding acquisition, writing – review & editing. WC investigation, methodology, writing – original draft. YT writing – review & editing. JW funding acquisition, writing – review & editing. WS funding acquisition, writing – review & editing, supervision.
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Fu, J., Chen, W., Tan, Y. et al. Experimental Study on Pore Variation and Meso-Damage of Saturated Sandstone Under Unloading Condition. Rock Mech Rock Eng 56, 4669–4695 (2023). https://doi.org/10.1007/s00603-023-03293-4
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DOI: https://doi.org/10.1007/s00603-023-03293-4