New utility locating technologies are combining to eliminate guesswork when construction takes place around underground utilities.
Underground utilities can become a nightmare for the site work or highway contractor. A fraction of an inch of contact with an excavator or even surface pressure from a track machine can damage or break a line. The result? Job progress stopped dead in its tracks while the repair costs start rolling in. Damaging an underground line can turn a potentially profitable project upside down quicker that any other construction catastrophe.
Line locating services provide minimal information — intermittent paint marks on the ground with no depth information provided. But in today's digital technology age, the hit or miss approach to dealing with costly underground installations is antiquated and creates unnecessary liability issues.
A survey firm in Florida has found a better way.
Southeastern Surveying and Mapping has devised a way to combine advanced technologies to obtain real-time utility location data. Precise depth as well as exact surface location information can be available for design and construction purposes.
Southeastern Surveying and Mapping has offices in Orlando and Chipley, Fla. The firm created a Sub Surface Utilities Engineering Department to specialize in services relating to the mapping and protection of underground lines.
Subsurface utility engineering is an engineering process for accurately identifying the quality of subsurface utility information needed for highway plans, and for acquiring and managing that level of information during the development for a highway project. The Federal Highway Administration estimates that for every dollar spent for S.U.E. services, $4.62 is saved in construction costs. FHA found that the cost of S.U.E. services is less than 0.5 percent of total construction costs, and the benefits include reduced construction costs, reduced liability and fewer schedule delays, as well as fewer contract claims and improved safety.
Southeastern's Subsurface Utilities Engineering division is managed by Darryll DeMarsh. Through education and experience, he has become an expert at this specialty work. DeMarsh aggressively maintains a hands-on approach to the projects under his responsibility.
Southeastern's crews use three technologies to determine and record this data.
One of them is ground penetrating radar (GPR). Southeastern uses a device called "The Noggin." This highly-portable radar transmitter/receiver is mounted on a wheeled carriage called a "SmartCart." The Noggin outputs data to a Digital Video Logger (DVL), which is mounted on the handlebars. The DVL has a video display that provides instant visual recognition of underground lines and cables as they are encountered.
Southeastern also uses vacuum excavation technology to expose the line, identify it and record its depth. The test hole is approximately 20.32 cms in diameter. Digging with conventional excavation equipment disturbs large areas, is constrained by vehicular traffic along the roadway and can damage other lines in the area. Settlement in backfill areas can create future hazards. Vacuum excavation eliminates these problems.
Finally, the company is putting GPS location technology to work. The company is using Topcon's HiPer Pro GPS+ survey system for several purposes. A map of the entire project site is loaded on the FC-100 field computer. Using Topcon's Pocket 3D software, the superintendent can locate his exact position. The FC-100 and HiPer Pro antenna can also be used on the SmartCart handle to record surface location data as lines are observed with GPR. After a test hole is opened, the GPS+ antenna is placed on a rover pole and lowered to the top of the line or cable. Depth is recorded on the field computer.
One project where use of new technology and the subsurface utility engineering approach have proven their value is on recent work on U.S. 441 in Leesburg, Fla. That stretch of highway has been suffering with traffic congestion for several years. The Florida Department of Transportation determined that a widening project was justified to alleviate the problem. Originally, the utility location was scheduled to take place in advance of the widening project. The urgency to resolve the traffic flow problem prompted the award of simultaneous contracts, and both phases are being completed at the same time.
The project in Leesburg adjoins two other FDOT US 441 widening projects currently under construction, with a combined cost of $68,212,222. D.A.B. Constructors was the successful bidder on all three projects.
For the preliminary design stage, FDOT contracted with Southeastern to perform a topographic survey and excavate 127 test holes for utility location. The road widening requires the storm system to be redesigned and relocated. Data on existing utilities was fundamental to a conflict-free design.
The city of Leesburg owns nearly all the utilities within the scope of the project. These include potable and reclaimed water, wastewater, natural gas, and electric. Florida Gas Transmission, Comcast and Sprint have the only other lines in the area. Because the right-of-way was limited, all utilities are being relocated to one common trench. Not only is less area required using the single-trench approach, but excavation costs are reduced substantially.
Southeastern is now contracted with Leesburg to mark, map, verify, and protect its utilities along the project path. As part of their services, they will lay out all proposed FDOT storm drain pipe and structures to further protect against conflicts as the relocation takes place. They will also produce as-builts on 300-foot stationing.
The simultaneous completion of both phases of the U.S. 441 project requires Southeastern to staff the project with multiple crews. Constant coordination is required among multiple subcontractors. They must locate existing lines to prevent damage during trenching and boring for new utilities, then protect the newly installed while the old are removed.
Hewitt Contracting, located in Leesburg, is completing construction of the new lines and removal of the old for all owners. They are operating on a labor and equipment basis, with each utility owner providing the materials for their respective line.
According to Willie McMillan, head of the Hewitt's utility division, coordinating, stockpiling and handling of multiple conduits, pipes and cables is one of the two biggest challenges of the job. The other is clean shooting bores under the highway, intersecting streets and myriad of driveways in the maze of underground obstructions.
Projects like this one show how new technologies (which are being developed at an increasing rate) can have real significance when they are applied to solve problems that contractors have struggled with for years. Southeastern Surveying and Mapping found a way to blend three advanced systems and create a long-needed solution for one of construction's biggest unknowns — what's buried in the ground.