Model-Based Deep Line Utility Survey

By John W. Jaeger, Senior Project Manager, Binkley and Barfield Inc. | April 2014, Vol. 69 No. 4

The successful use of the Dual Spar equipment prompted use on a gas line in the Monte Belvieu area of Texas. This line was reported to be 35-feet deep and efforts to designate it had been ongoing for over a month. At high cost, twelve, 36-inch diameter by 35-foot deep test holes had been excavated in the attempt to locate this line. Using the Dual Spar methodology, the gas line was designated in less than two hours and shown to be at a depth of 33.5 ±1.2 feet. The line was immediately excavated via hydro excavation at the new location and found. The depth of the line was surveyed at 34.1 feet (an eight-inch difference between the exposed depth and the remote sensing depth and within the reported error).

That same day, BBI went to another gas line location and used the Dual Spar to locate two lines crossing under Beltway 8. These lines had proven to be un-locatable by standard methods due to interference from electric towers. Both of these lines will be crossed by a directional bore. Knowing the horizontal and vertical locations of these lines to complete the design of the directional bore is critical.

Again the Dual Spar System quickly collected the X, Y and Z data on the two lines and work was completed within four hours. The collected data showed the gas line depths to be 16.1 (±0.9) and 15.4 (±0.8) feet deep at the crossing of the directional bore. The utility owners requested a QL-A Test Hole on each gas line at the crossing of the directional bore. The test holes were excavated at the locations the Dual Spar indicated and the depths were 16.8 and 15.8-feet deep (nine- and five-inches difference and within the confidence intervals reported by the software).

A short time later the utility provider requested another SUE QL-B Designation using the Dual Spar on a gas line running diagonally under Beltway 8. Improvements to an overpass required new piers going as deep as 60 feet and the diagonal running gas line threads the needle between them. The gas line was reported to be 48-feet deep and there had been numerous unsuccessful designation attempts over a period of a year. A 60-inch diameter by 50-foot deep test hole was also unsuccessful in finding the gas line. A smart pig had been used to give an approximate location of the gas line and showed the proposed pier locations to be within eight feet. The utility provider wanted additional verification of the gas line location and due to the depth, there wasn’t adequate time to perform another test hole excavation.