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TUNNEL INSPECTIONS AND MONITORING

 

The survey of the final lining intrados may be carried out with an accuracy better than 1 mm, which may be adjusted per the Client’s needs. The first survey provides a reference or baseline for future inspections or monitoring surveys of the tunnel in order to determine:

 

  • Any displacement (e.g., convergence or settlement of the ceiling), and/or
  • Any change in the lining defects: cracks (length, width, number), spalls (area and number), and water ingress.

 

The quantities to be surveyed (displacements and defects) are chosen by the Client. LRRT uses special lighting systems devised in order to evenly illuminate the lining even in dark situations, such as air ducts, and to ensure that the colours of the lining and its defects are reliably reproduced. For a COMPARISON WITH A LASER SCANNER LiDAR.

The speed of photo acquisition depends on: the accuracy required, the minimum distance between the cameras and the tunnel lining, and whether the tunnel is accessible to vehicles or not. LRRT has developed special technology in order to achieve the performance detailed in the following table (click to enlarge).

 

Close-up views of the photogrammetric model of a shotcrete liner in an underground excavation: (a) baseline (March 2013), (b) Survey 2 (May 2013); (c) Survey 3 (February 2014). It is evident that seepage through the lining has increased substantially over less than a year.

Here are coloured contours of the length of the displacement component orthogonal to the  shotcrete surface for an underground excavation: green means less than 1 mm; white means between 1 and 5 mm; red means over 5 mm. The displacements occurred over a period of 8 months.

 

The Figures below provide an example of a three-dimensional model of a road tunnel lining and its use in identifying lining defects.

Some of the cracks have been digitized in: the rightmost crack is a typical construction (pour) joint, but the others are not, and their orientations allow one to infer the causes of distress in a specific area of the lining. Such inferences are very difficult to be made while inspecting the tunnel and while mapping the cracks by hand. In addition, the orientation of the cracks is useful to determine the orientation of the grouting holes.

 

3D model of Liberty Tunnel Inbound Tube by the Ventilation Shaft. The next figures show close-up views of the circled spall.

 

Detail of spall by the Ventilation Shaft.

 

Foreshortened view of spall by the Ventilation Shaft.

 

Detail of exposed aggregate and rebar by the Ventilation Shaft.

 

Backside view of spall by the Ventilation Shaft to better appreciate spall depth and extent.

 

Closed green polyline to determine the area of the concrete spall by the Ventilation Shaft. The depth of the defect may be determined point by point.

 

Typical survey of existing cracks in a final lining.

 

Via Nazionale 206 - 38123 - Trento, Italy

 

Phone: +39-0461942345

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The survey of the final lining intrados may be carried out with an accuracy better than 1 mm, which may be adjusted per the Client’s needs. The first survey provides a reference or baseline for future inspections or monitoring surveys of the tunnel in order to determine:

TUNNEL INSPECTIONS AND MONITORING

  • Any displacement (e.g., convergence or settlement of the ceiling), and/or
  • Any change in the lining defects: cracks (length, width, number), spalls (area and number), and water ingress.

 

The quantities to be surveyed (displacements and defects) are chosen by the Client. LRRT uses special lighting systems devised in order to evenly illuminate the lining even in dark situations, such as air ducts, and to ensure that the colours of the lining and its defects are reliably reproduced. For a COMPARISON WITH A LASER SCANNER LiDAR.

The speed of photo acquisition depends on: the accuracy required, the minimum distance between the cameras and the tunnel lining, and whether the tunnel is accessible to vehicles or not. LRRT has developed special technology in order to achieve the performance detailed in the following table (click to enlarge).