Internal forces arising in the segmental lining of an EPB bored tunnel

This paper presents experimental data obtained by long-term monitoring of the strains occurring in several segments of a precast RC segmental lining adopted to support a bored tunnel. Careful and tight control of the strains was also carried out during the early installation stages, which only lasted a few hours. The strains were measured using vibrating wire gauges embedded in the segments during construction at the manufacturer’s plant. The measurements were recorded using a wireless data logger, which allowed accurate follow up of the strain changes in the segments beginning with the concreting stage and for a long time after the tunnel construction. With reference to the various construction stages, the measured strains are presented and discussed. Their maximum values are just a few hundred microstrains, making the thermal effects on the gauge readings significant. For this reason the problem of their elimination is briefly addressed in the paper. The process used to derive the internal forces in the lining is not at all straightforward and the paper describes the process and reports the obtained internal forces both in short- and long-term conditions.