Study on shear creep test and nonlinear model of granite structural plane under coupled freeze-thaw cycle and chemical corrosion

Abstract

To investigate the combined effect of freeze-thaw cycles and chemical corrosion on the shear creep characteristics of rock structural planes in cold regions, taking the granite structural planes of Huibai Tunnel in Jilin Province as the research object, microscopic structural observation and shear creep test were carried out on the structural surfaces treated by acidic, neutral and alkaline solution immersion and freeze-thaw cycles, analyzed the damage characteristics and creep mechanism of structural planes. The results show that: (1) With the increase of freeze-thaw and chemical corrosion, the structural plane of the mineral particles significantly reduced, the structural plane shows phenomena such as dissolution and hydrolysis, and the surface is gradually smoothed. (2) Compared with the natural condition, the instantaneous deformation of the samples under 20, 40, and 60 freeze-thaw cycles in H₂SO₄ solution increased by 47.43%, 64.52%, and 128.57%, the creep deformation increased by 36.58%, 53.68%, and 107.31%, and the instantaneous shear modulus decreased by 25.34%, 40.31%, and 64.35%. The instantaneous deformation, creep deformation and creep rate of the structural plane gradually increase with the increase of freeze-thaw and chemical corrosion, while the instantaneous shear modulus and long-term shear strength show a decreasing trend. (3) Compared with the natural condition, the instantaneous deformation of the samples in H₂SO₄, NaOH and NaCl solutions increased by 128.57%, 68.29% and 85.36% respectively under 60 freeze-thaw cycles, the creep deformation increased by 107.31%, 62.52% and 76.88% respectively, and the instantaneous shear modulus decreased by 64.35%, 50.31% and 56.54% respectively. The acidic H₂SO₄ solution has the greatest impact on the damage and creep parameters of the structural planes, followed by NaOH solution, with NaCl solution causing the least damage. Furthermore, in the damage process of structural planes, the freeze-thaw cycle and chemical corrosion promote each other mutually, since the combined influence of two-factor on damage and creep characteristics are greater than the influence of single factor. Based on the experimental results, considering the influence of freeze-thaw and chemical corrosion on model parameters, a nonlinear viscous element was introduced to describe the accelerated creep characteristics, the shear creep damage model of structural plane was established, and the reasonableness of the model was verified through test data. Finally, the three-dimensional roughness JRC^3D of the structural plane was selected as the evaluation index, and the influence of the three-dimensional roughness JRC^3D on the shear creep mechanical properties of the structural plane was discussed. The research results have guiding significance for the long-term stability evaluation of rock mass engineering in cold regions.