Railway tunnel 3D survey

Railway tunnel survey and structural inspection, Aghios Stefanos, Athens – Greece

Purpose

The Greek Railway Organization main railroad, to its northern exit from Athens, passes through a tunnel complex, consisting of four tunnels (two for each railway line), near the small city of Aghios Stefanos. The NE tunnel, approximately 200m long and 5m wide, was built from stones about 50 years ago. Due to suspected deformations of this tunnel in combination with known geological problems of the whole area, the Greek Railway Organizations ordered a stability check, along with a complete survey of the tunnel and the superjacent ground.

Project tasks

• Establishment of geodetic network (GGRS’87).
• TLS survey with Optech ILRIS3D:
  • 8 scanning positions (6 inside – 2 outside)
  • Average resolution 1-2 cm
  • Georeferencing: 8 conical targets, additional control points
• Conventional survey of superjacent ground surface above tunnel.
• Basic processing of TLS data and other measurements.
• 3D modeling of tunnel and superjacent ground, H and V section extraction.
• Inspection in comparison to theoretical geometry.

Results – Conclusions

The cross-section based evaluation and comparison of the surveyed tunnel wall to its theoretical geometry revealed large deformations at specific locations (e.g. section 15). These locations have been defined and mapped in detail and repairing actions have been designed. Tunnel has been closed until repair works will be executed. Further geological investigation defined the reason of the deformations to be the presence of slate (sch) and clay (PT) formations at the tunnel’s area and the existence of a possible fault between them.

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