This article described the triangulation cover used to survey the Du Toitskloof (Huguenot) Tunnel. A network based on permanent survey stations that connect at least three control points close to the western and eastern portals was selected. Connection between these groups of points via permanent beacons erected along the top of the mountain range was considered essential. For optimum results it was considered necessary to have distance measurements along all sides of the triangulation and for a simultaneous least squares adjustment using both sides and angles to be made for the entire network. A network height datum was selected at 400 m above mean sea level, this being the mean elevation of the tunnel portals. The selection of a local origin close to the meridian of the centre point of the tunnel would obviate corrections to spheroidal observed directions. To allow for possible additional long orientation, especially at the western portal where additional construction was planned, the local network would have to be oriented on the national system. The network could thus be completed on the plane with little or no special refinements to field observations being demanded from subsequent users during construction. Details of special requirements set to attain the required results were also provided. This included specifications for design of the points of the network, and beacon signals, instrumentation and data collection. A limited constraint solution using local origin and one additional station fixed on the national network was used. The two stations chosen were 4.7 km apart and situated close to the extremities of the network. The existing software developed by surveys and mapping was used to analyse the measurements. Early relative positional predictions were tested against those of the completed tunnel. An excellent closure error of 1/380000 or 12 mm over a distance of 4.8 km was obtained. (TRRL)

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  • Corporate Authors:

    South African Institute of Civil Engineers

    9 St Davids Place, Parktown, P.O. Box 62129
    Marshalltown,   South Africa 
  • Authors:
    • Rousseau, DPM
    • Hough, AJT
  • Publication Date: 1988-4

Media Info

  • Pagination: p. 171,173
  • Serial:

Subject/Index Terms

Filing Info

  • Accession Number: 00493087
  • Record Type: Publication
  • Source Agency: Transport Research Laboratory
  • Files: ITRD, TRIS, ATRI
  • Created Date: May 31 1990 12:00AM