Utilizing Laser Scanning Technology for Existing Conditions Surveying and Mapping

The Saint Lawrence Seaway Development Corporation (SLSDC) was planning to reconstruct a failing tainter valve at the Snell Lock located in Massena, New York. The SLSDC determined that the valve was not closing completely and may have been out of alignment. To confirm the alignment and determine the best course of action, the SLSDC retained Thew Associates to perform an existing conditions survey of the valve trunnions, guide bushings, culvert walls, bull nose plate, chimney, and strut arm (topside).

Thew Associates utilized a Riegl VZ-400i terrestrial laser scanner to perform the existing conditions survey of the tainter valve. The topside strut arm was referenced to the valve trunnions, guide bushings, bull nose plate, and culvert walls. A complete three-dimensional model of the tainter valve components to include the surrounding chimney and culvert was created using the terrestrial laser scanner.


The terrestrial laser scanner and survey crew were lowered into the chimney and culvert by crane and man basket. Scanning in the culvert shaft was performed on a tripod at ten-foot intervals along the centerline of the culvert. The crew and scanner were then lifted into the chimney to begin scanning the vertical portion of the project. Anchor bolts mounted on the face of the chimney wall at 10-foot intervals, beginning 5 feet from the bottom of the shaft and ending 1-foot from the top of the shaft were required to mount the scanner on a pre-fabricated mount. The crew mounted the scanner and were subsequently lifted out of the chimney before remotely triggering the VZ-400i allowing the scanner to measure the existing conditions at each vertical increment.

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The data was post processed and a 3D model was prepared. The required measurements were extracted from the 3D model and expressed on 2D plan section view mapping. SLSDC rebuilt the components in the horizontal shaft using the information from the existing conditions survey and successfully installed a new tainter valve that is now operational.



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