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International Journal of Frontiers in Engineering Technology, 2021, 3(9); doi: 10.25236/IJFET.2021.030910.

Loading-Unloading Mechanical Characteristics and Constitutive Model of Porous Rock


Zhe Liu, Jiajing Li, Wei Wang

Corresponding Author:
Zhe Liu

School of Petroleum Engineering, Guangdong University of Petrochemical Technology, Maoming 525000, Guangdong, China


This paper studies the stress-strain relationship of rock in the process of loading and unloading. Taking sandstone as an example, conventional triaxial loading and unloading experiments are carried out. The non-linear characteristics of rock during the post-peak unloading stage are analyzed, and the damage variable of rock is defined. An elastic modulus model for describing the stress-strain relationship during post-peak unloading is presented. The relationship between the axial strain and the radial strain in the loading-unloading process is analyzed; the Poisson's ratio model in unloading process is obtained. The D-P plastic model is introduced to modify the hardening function according to the plastic hardening characteristics of sandstone; a damage model associated with equivalent plastic strain is established. The computational model is matrixed and then calculated numerically. In the process, the following conclusions are drawn: (1) The porous rock shows obvious non-linear characteristics during loading. With the increase of body stress, the elastic modulus of rock increases gradually. (2) When the axial stress is greater than the confining pressure in the process of unloading rock after peak load, Stress-strain can be described by multiplying the elastic modulus model of the pre-peak elastic stage by the continuity factor. (3) With the increase of equivalent plastic strain, Poisson's ratio increases first, then decreases, and finally tends to be stable. In the post-peak unloading process, the equivalent plastic strain does not change, while the Poisson's ratio remains unchanged. The results show that the proposed model can reflect the stress-strain law of rock during post-peak unloading. 


Rock Mechanics, Stress-Strain Relationship, Modulus of Elasticity

Cite This Paper

Zhe Liu, Jiajing Li, Wei Wang. Loading-Unloading Mechanical Characteristics and Constitutive Model of Porous Rock. International Journal of Frontiers in Engineering Technology (2021), Vol. 3, Issue 9: 56-65. https://doi.org/10.25236/IJFET.2021.030910.


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