A preliminary study of the parameters influencing the perfomance of two-component backfill grout

In the mechanized tunnelling with Tunnel Boring Machines (TBM), the filling process of the tail void that is created simultaneously to the advancement of the TBM between the excavation profile and the extrados of the precast concrete segments of the final lining takes on particular importance. The effectiveness of this operation depends on the injection methods and the mechanical characteristics of the injected material, which is crucial for the success of the excavation, the correct positioning of the lining elements and the reduction of the effects induced on the surface (settlements). This note presents the preliminary results of a study on the two-component backfill grout commonly used during mechanized tunnelling to fill the annular gap between the excavated soil and the lining. The research, carried out by GEEG srl, startup of Sapienza University of Rome at the geotechnical laboratory of Dept. of Structural and Geotechnical Engineering and the chemical laboratory of Dept. of Chemical Engineering, Materials, Environment, is still ongoing and aims to a better comprehension of the chemical and physical factors that influence the performance of these mixtures and to the standardization of the test procedures to be applied in other to measure them. In particular, the data here presented explore the influence of the composition and the methods of preparation of the specimens on the mechanical properties of the grout obtained with alkaline and alkali-free accelerator.