Hard rock TBM performance: Preliminary study based on an exploratory tunnel in the Alps

Abstract

Explorative tunnels are one of the best ways to assess the rock quality in the preliminary stage of a long tunnel excavation project: this strategy allows predictions for evaluating, with good accuracy, methods, costs, and technical problems related to the excavation of the main tunnel. The paper presents the first results of a study carried out on a 6.3 m diameter exploratory tunnel excavated in hard rock by TBM. A study of the data taken during the TBM's advancement is ongoing. The evaluation of the rock cutting efficiency, through the excavation specific energy (SE) is performed. A method for the evaluation of the grain size distribution of the muck produced during the excavation is proposed. The development of Matlab code to automatically analyze the machine acquired data in relation with the rock mass characteristics is reported in the paper.

La Maddalena exploratory tunnel

“…The minute gneiss and quartzitic mica schist (AMD) as well as the Clarea mica schists (CL) show a decrease in rock mass quality. The rock mass quality is linked to the schistose and micaceous nature with conditions being in general of lower quality also due to a generally greater degree of fracturing of the rock mass with discontinuities often set along the same foliation [6].…”

“…Furthermore, the recorded values were lower than the expected minimum and maximum inflows in steady state conditions, despite the measured data referring to a transient value of total inflow that should be higher than the stabilized flow rate. This difference is due to an overestimation of the expected inflow for some hydrogeological units such as Quaternary deposits (Q), Carniole (1) and calcareous schists (6).…”

Determining the Particle Size of Debris from a Tunnel Boring Machine Through Photographic Analysis and Comparison Between Excavation Performance and Rock Mass Properties

“…To face the above problems, the present study proposes a methodology for the analysis of the debris from TBM through photographic analysis. This method, previously adopted by Rispoli et al (2016), allows to quickly analyze a large volume of debris (about 3 m 3 for each sampling), with contained costs: it does not need an analysis laboratory and requires little labor (both the sampling and the processing phases may be carried out by one operator). The method, due to its simplicity, is systematically implementable (on a daily basis, together with the other investigations carried out during the progress of TBM) and not interferes with the excavation cycle, since the sample is taken from the piles of debris outside the tunnel.…”