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Three-dimensional laser scanning for geometry documentation and construction management of highway tunnels during excavation.

Gikas V - Sensors (Basel) (2012)

Bottom Line: This paper discusses the use and explores the potential of laser scanning technology to accurately track excavation and construction activities of highway tunnels.Also, it discusses the planning, execution, data processing and analysis phases of laser scanning activities, with emphasis given on geo-referencing, mesh model generation and cross-section extraction.Specific case studies are considered based on two construction sites in Greece.

View Article: PubMed Central - PubMed

Affiliation: School of Rural and Surveying Engineering, National Technical University of Athens, 9 I Polytechniou Str., Zographou, Athens 15780, Greece. vgikas@central.ntua.gr

ABSTRACT
Driven by progress in sensor technology, computer software and data processing capabilities, terrestrial laser scanning has recently proved a revolutionary technique for high accuracy, 3D mapping and documentation of physical scenarios and man-made structures. Particularly, this is of great importance in the underground space and tunnel construction environment as surveying engineering operations have a great impact on both technical and economic aspects of a project. This paper discusses the use and explores the potential of laser scanning technology to accurately track excavation and construction activities of highway tunnels. It provides a detailed overview of the static laser scanning method, its principles of operation and applications for tunnel construction operations. Also, it discusses the planning, execution, data processing and analysis phases of laser scanning activities, with emphasis given on geo-referencing, mesh model generation and cross-section extraction. Specific case studies are considered based on two construction sites in Greece. Particularly, the potential of the method is examined for checking the tunnel profile, producing volume computations and validating the smoothness/thickness of shotcrete layers at an excavation stage and during the completion of excavation support and primary lining. An additional example of the use of the method in the geometric documentation of the concrete lining formwork is examined and comparisons against dimensional tolerances are examined. Experimental comparisons and analyses of the laser scanning method against conventional surveying techniques are also considered.

No MeSH data available.


Related in: MedlinePlus

Example of a tunnel portion generated using a 2D mesh algorithm (a); and a successfully constructed 3D irregular mesh model (b); The problems associated with the use of a 2D mesh algorithm are evident at the top areas where the TIN triangles are actually “filling up” the space rather than forming a realistic representation of the tunnel surface. Also, at the sides of the tunnel the TIN (Triangulated Irregular Network) triangles are fictitiously elongated indicating failure in the 2D mesh model construction.
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f5-sensors-12-11249: Example of a tunnel portion generated using a 2D mesh algorithm (a); and a successfully constructed 3D irregular mesh model (b); The problems associated with the use of a 2D mesh algorithm are evident at the top areas where the TIN triangles are actually “filling up” the space rather than forming a realistic representation of the tunnel surface. Also, at the sides of the tunnel the TIN (Triangulated Irregular Network) triangles are fictitiously elongated indicating failure in the 2D mesh model construction.

Mentions: The second method presupposes the generation of a full 3D mesh model of the tunnel tube. Generally, the mesh generation refers to the practice of generating a polygonal or polyhedral mesh in the form of a 3D grid that approximates a geometric domain. Various algorithms exist for this purpose such as the polygon mesh and Delaunay triangulation [38]. Depending on specific application needs two types of mesh models can be considered. Firstly, regular type mesh models which constitute a mathematical representation of the surface in question, and secondly, irregular (or unstructured) type mesh models the geometric properties of which cannot be described by a regular mathematical surface. In tunnel surveying applications the regular mesh models is not an option. This is because the surface of a tunnel (especially at the early stages of construction), is so irregular that it cannot be approximated by a mathematical surface. Also, it should be noted that, the common 2D meshing algorithms usually employed for the generation of DTMs in road design, topographic surveying and GIS software packages cannot be used for the creation of a fully 3D irregular mesh model. This restriction stems from the fact that all ordinary 2D mesh algorithms assume a one to one correspondence between the scanned points and the reference plane (datum). Apparently, this is not the case in tunnel surveying as for every individual point fix on the projection surface (i.e., the cross-section) correspond more than one point fixes on the tunnel wall. Today, the mesh modeling algorithms applied in TLS software have been specifically designed to face successfully this problem; and therefore, the mesh modeling method has prevailed in tunnel survey works. However, there exist situations where the processing analyst/engineer shall need to manually proceed to corrective actions to ensure quality assurance in the final product. Figure 5 shows an example of a successfully (3D) and an erroneously (2D) produced mesh model.


Three-dimensional laser scanning for geometry documentation and construction management of highway tunnels during excavation.

Gikas V - Sensors (Basel) (2012)

Example of a tunnel portion generated using a 2D mesh algorithm (a); and a successfully constructed 3D irregular mesh model (b); The problems associated with the use of a 2D mesh algorithm are evident at the top areas where the TIN triangles are actually “filling up” the space rather than forming a realistic representation of the tunnel surface. Also, at the sides of the tunnel the TIN (Triangulated Irregular Network) triangles are fictitiously elongated indicating failure in the 2D mesh model construction.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3472883&req=5

f5-sensors-12-11249: Example of a tunnel portion generated using a 2D mesh algorithm (a); and a successfully constructed 3D irregular mesh model (b); The problems associated with the use of a 2D mesh algorithm are evident at the top areas where the TIN triangles are actually “filling up” the space rather than forming a realistic representation of the tunnel surface. Also, at the sides of the tunnel the TIN (Triangulated Irregular Network) triangles are fictitiously elongated indicating failure in the 2D mesh model construction.
Mentions: The second method presupposes the generation of a full 3D mesh model of the tunnel tube. Generally, the mesh generation refers to the practice of generating a polygonal or polyhedral mesh in the form of a 3D grid that approximates a geometric domain. Various algorithms exist for this purpose such as the polygon mesh and Delaunay triangulation [38]. Depending on specific application needs two types of mesh models can be considered. Firstly, regular type mesh models which constitute a mathematical representation of the surface in question, and secondly, irregular (or unstructured) type mesh models the geometric properties of which cannot be described by a regular mathematical surface. In tunnel surveying applications the regular mesh models is not an option. This is because the surface of a tunnel (especially at the early stages of construction), is so irregular that it cannot be approximated by a mathematical surface. Also, it should be noted that, the common 2D meshing algorithms usually employed for the generation of DTMs in road design, topographic surveying and GIS software packages cannot be used for the creation of a fully 3D irregular mesh model. This restriction stems from the fact that all ordinary 2D mesh algorithms assume a one to one correspondence between the scanned points and the reference plane (datum). Apparently, this is not the case in tunnel surveying as for every individual point fix on the projection surface (i.e., the cross-section) correspond more than one point fixes on the tunnel wall. Today, the mesh modeling algorithms applied in TLS software have been specifically designed to face successfully this problem; and therefore, the mesh modeling method has prevailed in tunnel survey works. However, there exist situations where the processing analyst/engineer shall need to manually proceed to corrective actions to ensure quality assurance in the final product. Figure 5 shows an example of a successfully (3D) and an erroneously (2D) produced mesh model.

Bottom Line: This paper discusses the use and explores the potential of laser scanning technology to accurately track excavation and construction activities of highway tunnels.Also, it discusses the planning, execution, data processing and analysis phases of laser scanning activities, with emphasis given on geo-referencing, mesh model generation and cross-section extraction.Specific case studies are considered based on two construction sites in Greece.

View Article: PubMed Central - PubMed

Affiliation: School of Rural and Surveying Engineering, National Technical University of Athens, 9 I Polytechniou Str., Zographou, Athens 15780, Greece. vgikas@central.ntua.gr

ABSTRACT
Driven by progress in sensor technology, computer software and data processing capabilities, terrestrial laser scanning has recently proved a revolutionary technique for high accuracy, 3D mapping and documentation of physical scenarios and man-made structures. Particularly, this is of great importance in the underground space and tunnel construction environment as surveying engineering operations have a great impact on both technical and economic aspects of a project. This paper discusses the use and explores the potential of laser scanning technology to accurately track excavation and construction activities of highway tunnels. It provides a detailed overview of the static laser scanning method, its principles of operation and applications for tunnel construction operations. Also, it discusses the planning, execution, data processing and analysis phases of laser scanning activities, with emphasis given on geo-referencing, mesh model generation and cross-section extraction. Specific case studies are considered based on two construction sites in Greece. Particularly, the potential of the method is examined for checking the tunnel profile, producing volume computations and validating the smoothness/thickness of shotcrete layers at an excavation stage and during the completion of excavation support and primary lining. An additional example of the use of the method in the geometric documentation of the concrete lining formwork is examined and comparisons against dimensional tolerances are examined. Experimental comparisons and analyses of the laser scanning method against conventional surveying techniques are also considered.

No MeSH data available.


Related in: MedlinePlus