Experimental studies on the chemical and mechanical characteristics of backfill grouts

One important operation for the successful mechanized excavation of a tunnel is the immediate filling of the annular gap progressively created between the final tunnel lining and the excavated soil/rock profile. This task, known as backfilling, consists in the injection of mortars, usually two-component grouts, at the end of the TBM shield.

GEEG has been developing research activities on this issue, with the aim of contributing to the understanding of the chemical and physical factors that influence the performance of these mixtures and to the standardization of the relevant test procedures. These materials are entrusted with various functions, such as ensuring uniform contact between the lining and the surrounding soil to avoid surface settlements and/or concentrated loads, supporting the lining rings, withstanding part of the loads transmitted by the TBM during the thrust and integrating the waterproofing; it seems therefore evident that these mixtures must meet certain requirements in terms of workability, gel-time and mechanical behaviour.

The study that GEEG is developing aims to identify the factors that most influence the performance of the two-component mixtures, through the adoption of repeatable sample preparation procedures (able to replicate the mixing process and the injection conditions) and laboratory tests for the measurement of the strength, stiffness and durability of these materials during ageing.