Ultrasonic measurements for assessing the elastic parameters of two-component grout used in full-face mechanized tunnelling

The use of shield machines and instantaneous segment linings for tunnel construction is one of the most used tunnelling methods today. Despite a large number of applications in different tunnelling projects all around the world, knowledge of the behaviour of two-component grout is quite limited, mainly due to the fast hardening process that inhibits using the classic approach for concrete characterization. In the present work, an innovative approach based on ultrasonic measurements is introduced, aimed to characterize the elastic properties of this innovative backfilling material. Specifically, ultrasonic pulse velocity was applied to two-component grout samples to describe the interesting and fast evolution of the material from the mixing phase until 6 months of curing using geophysics parameters. The dynamic Young’s modulus (E) and the dynamic shear modulus (G) exhibited a clear increasing trend, starting from values of a few tens of MPa to final values equal to 1000 MPa and 340 MPa, respectively. The Poisson’s ratio (ν), close to the value of incompressible materials (0.5) at the short curing time, exhibited a decreasing trend, reaching roughly 0.445 after 3 months of curing.