Issue 66

W. Frenelus et alii, Frattura ed Integrità Strutturale, 66 (2023) 56-87; DOI: 10.3221/IGF-ESIS.66.04

losses. In order to better control critical damage in the Kaidagu tunnel project (China), a monitoring program was operated by distributed fiber optic sensors installed in the damaged lining [77]. After nearly a year of monitoring, the distributed deformations recorded by the fiber optic sensors have made it possible to highlight the vertical and oblique ovalizations of the tunnel lining [77]. Fig. 9 illustrates the installation of fiber optic sensors in the Kaidagu tunnel lining.

Figure 9: A view of fiber optic sensors installed in the Kaidagu tunnel lining (after Sui et al. [77], with permission from Elsevier).

Tunnel operating age when monitoring assessment

Sensor Capability

Accuracy Range

Study

Study case

Location

Sensor

Monitoring Results

Identification and collection of monitoring information, control the structural stress in tunnel. Detection of lining conditions in tunnels: thickness of first and second lining, boundary between the linings, identification of void layer and Rebar. Evaluation of the contact pressure between surrounding rocks, primary and secondary linings. Measurement of strains in lining in bending mode, Measurement of shear strain amount in linings and its joints

Vibrating wire sensors, surface strain gauges, concrete strain gauges, pressure cells

Tendency of support pressure transfer from the primary to secondary

Liu et al. [78]

Lianchengshan Tunnel

China

No data

30 years

lining. Unstable structural stress.

Decreased secondary lining thickness by 19.39% in one tunnel, and in the others it is between 0 and 1.71%.

Tunnels in South-link Line Railway of Taiwan

Puntu et al. [79]

1000 MHz

20 years

China

VMGPR system

The bearing capacity of the tunnel can withstand the contact pressure between surrounding rocks, supports and linings Peak bending strains detected, the linings underwent rotation, and then significant compressive strains. Peak shear strains measured

Wang et al. [70]

0.01MPa - 5 MPa

 3 months

Minxian Tunnel

China

Pressure sensors

Gue et al. [80]

  30 (BOTDR)

Royal Mail Tunnel

United Kingdom

BOTDR system, and LPDT

97 years

Table 3: A summary of common sensors used in primary and secondary tunnel lining monitoring

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