Viscoelastic–plastic rheological model and its application to tunnels

Abstract Tunnels exhibit obvious continuous deformation during excavation and operation. This behavior is closely associated with the time-dependent behavior of rocks, which is induced by groundwater level fluctuation. This paper proposes a rheological model consisting of a Hooke elastomer, Kelvin body, and novel plastic element in series (called the HKP model) to describe the creep response of rocks with consideration to groundwater change characterized by dry–wet cycles. First, dry–wet cycle creep tests were carried out to investigate the time-dependent behavior, that is, the creep behavior of sandstone. Then, the creep equation of the viscoelastic–plastic model was derived, and the damage coefficients under the effect of dry–wet cycles and time were obtained. Finally, the HKP model was established to investigate the continuous deformation during tunnel excavation. The results reveal that dry–wet cycles have obvious effects on the physical properties and creep behavior of sandstone. The creep behavior of sandstone undergoes three stages, namely, the decaying, steady, and accelerated stages, which can be reasonably described by the proposed HKP model. Tunnels exhibit obvious creep behavior owing to excavation. The proposed model can accurately predict tunnel deformation in practice. Thus, the HKP model can help in establishing tunnel maintenance strategies to ensure long–term safety.