Study on a Creep Constitutive Model of Phyllite Considering the Coupling Factors of Bedding, Confining Pressure, and Water Saturation

Layered phyllite excavation works show very strong creep behavior when encountering water, and the creep characteristics are greatly affected by bedding and the stress environment. Therefore, a creep test of saturated phyllite is carried out to study the creep characteristics of saturated phyllite under different bedding and confining pressure conditions, establish a creep constitutive model that can accurately express the coupling relationship between various factors, and reveal the coupling effect of the bedding and confining pressure on the creep of saturated phyllite. The results show that (1) in the case of uniaxial compression creep, the relationship between parameter <i>E</i> ₁ and bedding dip angle β shows a "<i>U</i>"-type relationship, and <i>E</i> ₂, <i>E</i> ₃, η₁, and η₂ all have a "<i>W</i>"-type relationship with the bedding dip angle. (2) During triaxial compression creep, <i>E</i> ₁, <i>E</i> ₂, <i>E</i> ₃, η₁, and η₂ exhibit a bedding dip angle β in a "<i>U</i>" shape; as the bedding angle gradually increases from 0° to 90°, the creep parameters all show a law of first decreasing (reaching the minimum when the bedding angle is 45°) and then increasing. (3) When the confining pressure is 15 MPa and the bedding angle is 0° and 90°, the triaxial creep fitting parameters are geometrically multiplied compared with the uniaxial creep parameters with the same inclination, which indicates that the confining pressure has an inhibitory effect on the creep of the bedding angle of 0° and 90°, while the bedding angle of 30°∼60° has a small increase in the creep fitting parameters, and its deformation and damage are mainly controlled by the bedding. (4) The uniaxial and triaxial creep simulation results of the FLAC^3D constitutive model are in good agreement with the test results, which verifies that the secondary development of the creep constitutive model is successful and reliable.