Viscoelastic–plastic rheological model and its application to tunnels

Abstract

Tunnels exhibit obvious continuous deformation during excavation and operation. This behaviour is closely associated with the time-dependent behaviour of rocks, which is induced by groundwater-level fluctuation and prolonged periodic rainfall infiltration. 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 considering the characteristics of dry–wet cycles. First, dry–wet cycle creep tests were carried out to investigate the time-dependent behaviour: that is, the creep behaviour 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 continuous deformation during tunnel excavation. The results reveal that dry–wet cycles have obvious effects on the physical properties and creep behaviour of sandstone. The creep behaviour of sandstone undergoes three stages – namely, the decaying, steady and accelerated stages – that can be reasonably described by the proposed HKP model. In practice, the proposed model can accurately predict the creep behaviour of rocks in tunnels owing to excavation. Thus, the HKP model can help in establishing tunnel maintenance strategies to ensure long-term safety.