Spalding DeDecker uses 'old' technology to finish underground tunnel surveying project

By Catherine DeDecker

DETROIT, March 21, 2007 -- Can using old technology be considered innovative? Yes, when doing so is the best, most accurate and efficient way to successfully solve a problem and complete the project. That is what Spalding DeDecker Associates (SDA), a Detroit-based civil engineering firm, did on the Maumee River East Side Watermain Phase II Project.

On the Maumee River project, SDA's surveyors were responsible for ensuring that the tunnel under construction would connect with an existing construction shaft on the far side of the river. The location and scope of the project introduced a number of constraints on typical surveying tools, leading SDA to choose the Gyroscope, a more traditional tool used for mining in the 1960s.

Typically Global Positioning Systems (GPS) technology is used for surveying projects, but for this project GPS was not an option because the tunnel eliminated the required line of sight to the satellites. Complicating matters more was the lack of back-sight available for surveying the tunnel. There was potential for a huge horizontal error with a mere 24 feet available for a back-sight that had to be projected sixteen hundred feet and hit the centerline of the shaft on the other side of the river.

Rather than risking the error, SDA mounted the Gyroscope on the top of a Wild T2 theodolite to measure angles and then aligned the theodolite telescope to true north utilizing the Gyroscope. Following assembly, the Gyroscope was deployed and allowed to run up to its full operating speed of 22,000 revolutions per minute. The gyroscope was then released and the "Turning Point Method" (TPM) was implemented.

The TPM allowed SDA to determine the precise direction of true north and also helped to accurately reach turning points. At least three turning points were observed, from which the horizontal circle reading representing true north was computed.

SDA used the Gyroscope and Wild T2 theodolite to precisely measure the angle of the tunnel on the ground surface before entering the tunnel. Once the equipment was positioned in the shaft, the orientation process was repeated to once again point the instrument toward true north and then to the actual bearing of the survey baseline.

Providing an accurate baseline was paramount for this project because the tunnel provides safe and reliable water service to the City of Toledo and surrounding communities for current use and future growth.

Thanks in part to SDA's precision and diligence, the East Side Watermain is able to provide improved water service. Residents of the southern and western portions of Toledo's distribution system will receive increased water pressure. The project will also strengthen the eastern portion of the system by increasing water availability.

In addition to these upgrades, the project will increase the reliability of the system by providing an additional river crossing and increase the overall efficiency of the system by reducing system pressure losses.

SDA's innovative thinking on this project won them a Surveying Honorable Conceptor award from the American Council of Engineering Companies of Michigan (ACEC/M) and the Michigan Society of Professional Engineers (MSPE).

Spalding DeDecker Associates Inc. (www.spaldingdedecker.com) is an employee-owned civil engineering and surveying and mapping firm. Utilizing a solutions-based methodology, SDA approaches every project with innovative technology, dedicated team members and a commitment to providing value to every client on every project.

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