Assessment of a New Time-dependent Constitutive Model for Shotcrete in Tunneling

ABSTRACT: The material behavior of shotcrete significantly affects the stability of tunnels. Shotcrete behaviors, such as modulus and compressive strength, are notably time-dependent. Furthermore, the freshly applied shotcrete is subjected to loading immediately after application, making a realistic representation of this material crucial in numerical modeling. Although a few creep models are available, they do not accurately represent the time-dependent behavior of shotcrete, especially at early ages. The time-dependent behavior of shotcrete has been under investigation for several years in our institution. Recently, the Lubby2-SB constitutive law, which describes the creep behavior of shotcrete, was developed at Leibniz University Hannover. Unlike previously developed Lubby2-SB and built-in constitutive models in FLAC 3D, the new model considered the evolution of modulus to represent the creep behavior of shotcrete. In this paper, the assessment and suitability of the implemented formulation of shotcrete for Lubby2-SB constitutive law were carried out, and a good agreement was revealed from a comparison between analytical and numerical solutions. The new time-dependent material law's applicability was verified by modeling a three-dimensional tunnel. Moreover, a comparison between a few creep models and a new model demonstrated that the newly developed shotcrete model more accurately simulates the creep behavior of shotcrete.