Issue 66

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

The lithology along the tunnel alignment is mainly composed of argillaceous sandstone and sandstone. However, the argillaceous sandstone is more predominant and is initially broken with many spectacular fractures. The surrounding environment of the tunnel is classified as soft rocks because of its low uniaxial compressive strength which is less than 10 MPa. In spite of drill-and-blast excavation method provokes more additional damage to the host rocks than those caused the TBM [37], it was adopted with reasonable sequence to excavate the Weilai tunnel, due to complexity associated with the site. Groundwater is relatively abundant in aquifers close to the surrounding rocks. As a result, geohazards such as groundwater inflows occurred during the construction of the tunnel. On top of that, the tunnel experiences strong creep and exhibits large convergence deformations. To assess the convergence deformation of the tunnel, traditional monitoring method was carried out with the Total station and convergence gauges where monitoring data were taken for 27 days. The final cross-section size of the tunnel, the disposition of the monitoring points, and an illustration of monitoring operation are illustrated in Fig. 16. Thereby, based on the on-site monitoring data, the evolution of tunnel convergence deformation is shown in Fig. 17.

Figure 16: Tunnel cross-section size, monitoring arrangement and illustration

Figure 17: Convergence deformation of the tunnel based on-site monitoring data

A robust support scheme has been designed to ensure the long-term safety and stability of the tunnel. It is composed of “Pressure aid + deep grouting + fully grouted rock bolts + fully grouted cable bolts + steel arch + secondary lining”. Nevertheless, due to the overall severe conditions of the tunnel environment, in order to effectively guarantee long-term

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