Rock-concrete composite specimens with different interface inclination angles: Creep characteristics and nonlinear damage constitutive model

Abstract

Weak rock-concrete interfaces significantly affect the stability of underground supporting structures. This study aims to investigate the effects of interface inclination on the creep behavior and failure mechanisms of composite specimens. Seven rock-concrete composite specimens with different inclination angles under hydrothermal curing at 60 °C were prepared, and uniaxial and graded loading creep tests were completed. The results show that with increasing interface inclination, the compressive strength of the composite specimens initially decreases and then increases, with the minimum strength observed at inclinations between 60° and 75°. Three typical failure patterns were identified: axial failure, composite failure, and interface failure. The creep failure strength exceeded the uniaxial compressive strength, indicating improved time-dependent deformation resistance under elevated temperature curing. The instantaneous strain initially decreases and then increases as the interface inclination angle grows. Compared to 0° inclination, specimens with 45°, 60°, 75°, and 90° inclinations exhibited reductions in instantaneous strain of 2.64%, 18.84%, 23.29%, and 0.73%, respectively. The steady-state creep rate and creep ratio exhibited a decrease-stabilization-increase trend with increasing stress levels. Creep strain increased with increasing stress levels for all inclinations, with a sharp increase near the failure stage. A nonlinear constitutive model considering interface inclination and creep damage was developed based on damage theory. A nonlinear damage-based constitutive model incorporating interface inclination effects was developed, and its theoretical predictions closely matched the experimental data in all creep stages. These findings provide a quantitative understanding of creep failure mechanisms in rock-concrete interfaces and provide practical references for enhancing the safety of underground support systems.

Keywords

rock-concrete composite / interface inclination / stress level / creep / nonlinear damage model

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