- SPECIAL REPORTS
- THE MAGAZINE
Underground utilities are a major expense in today's construction industry. The cost of the labor, materials and equipment required to install these lines is often a key item in a land development budget. Once these utilities are in the ground, they present ongoing challenges for the site work contractor.
Delays in construction projects due to utility conflicts happen on a regular basis, and often result in escalated costs to the contractor and owner. These conflicts occur when a utility cannot be precisely located or its depth is unknown. Damage to underground utilities during site work and excavation operations can cost utility companies, contractors and owners huge sums of money, as well as cause major inconvenience to the public dependent on them. In most cases, however, these damages can be prevented.
Line location services are available throughout the country, but the system is far from perfect. A narrow corridor within which the subject utilities are believed to exist is marked on the ground. In the majority of cases, precise depth information in advance of excavation is not available; depth can only be determined by exploratory excavations in areas where potential conflicts may arise, particularly with the construction of new storm drainage and sanitary sewer installations. A few inches of intrusion can mean the difference between a successful dig or a breach that shuts the job down and costs thousands of dollars in delays and repairs to the project. But there is a solution to this necessary task, and one land surveying company in Orlando, Fla., is utilizing it with success.
Dynamic Surveying Company Finds a SolutionSoutheastern Surveying and Mapping Corporation (SSMC), founded in 1972 as a traditional surveying firm, today employs 12 professional licensed surveyors and one professional engineer, and maintains 20 field crews. Even in today's highly competitive market, this company is thriving-much due to its resourcefulness. SSMC has developed a new and unique service for the construction industry: real-time utility location. By combining ground penetrating radar, GPS and vacuum technologies, SSMC has created a utility locating service that requires minimal intrusion of the surface, records exact position data (including depth) and safely exposes surfaces with the force of air for a faster and more accurate way to expose underground utilities.
The service springboards off the model of Subsurface Utility Engineering (SUE), 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," according to the U.S. Department of Transportation Federal Highway Administration. This process requires site investigation and records research, and uses sophisticated line locating equipment and surface and subsurface detection methodology. Non-destructive air and/or hydro vacuum excavation machinery is used to safely expose and record all pertinent utility information.
The Federal Highway Administration has determined the cost of using SUE to amount to less than half of one percent of total construction costs, and has estimated a savings of $4.62 for every dollar spent for these services. Similar savings can also be achieved for other types of construction. The benefits of using SUE on a construction project include reduced liability, reduced construction costs, reduced schedule delays and reduced contract claims. Most importantly, SUE increases site safety by decreasing the amount of utilities cut during excavation.
Darryll DeMarsh heads the Sub Surface Utilities Engineering Department of SSMC. He has completed extensive training and continuing education courses in this field of expertise, attaining certification as a ground penetrating radar technician. He has worked with SUE matters since he was 19 years old. In 2000, he was appointed to manage this division and is responsible for coordinating, estimating, managing and administrating utility projects performed for design and relocation purposes. DeMarsh takes a hands-on approach to ensure compliance with schedules and budgets, and backs SSMC's corporate motto: "There is no such thing as "We can't do it.'"
Tools of the TradeDeMarsh and his colleagues at SSMC combined some of today's most economical, accurate and non-intrusive equipment to form an effective, safe and fast method of locating, verifying and exposing utilities on jobsites. Here's what they put to use:
Ground Penetrating Radar UnitGround Penetrating Radar (GPR) enables survey crews to actually see underground. SSMC crews use a device called the "Noggin" manufactured by Sensors & Software Inc. (SSI, Mississauga, Ontario, Canada). This instrument is a 25" x 16" x 9" 250 MHz antenna and weighs 16 pounds. For the purposes of underground utility location, it is mounted on a SSI rolling carriage called a "SmartCart" that looks much like a high-wheeled lawn mower.
The Noggin outputs digital data and timing information that is transmitted to a Digital Video Logger (DVL) for display and recording, which is mounted to the handlebar of the Noggin. The display shows a series of stratified lines indicating the soil beneath the surface. An underground pipe or cable appears as a rising hyperbolic disturbance with an apex just above the top of the line.
GPS and Data Collection SystemSSMC uses the Topcon (Livermore, Calif.) HiPer Pro GPS+ survey system for several important tasks. Additionally, an FC-100 field computer operating with Topcon's Pocket 3D software is mounted to the cart handle with a conventional rover pole. The HiPer Pro rover antenna is mounted on a pole attached to the SmartCart. The FC-100, loaded with the project design files, is used to record exact position data, including depth, of the utilities.
SSMC's job superintendent also uses the HiPer Pro GPS+ system to orient himself on the project and check design features right from his truck. The GPS+ rover antenna is placed on the roof of the truck with a magnetic mount. His FC-100 rides with him in the cab. Wireless communication between the antenna and the field computer enables him to find his location on the job without any cable connections.
The Topcon HiPer Pro GPS+ system offers several advantages for SSMC's high-tech field crews. Four-mile coverage expedites work along linear projects such as transportation corridors. The GPS+ feature enables access to both GPS and GLONASS satellites, making numerous additional satellites available to the crews. Wireless communication between field controllers, rovers and base antennae facilitates field work and eliminates disruptions from lost or damaged cables.
Vacuum ExcavationVacuum excavation is a technology that enables exposure of underground lines with no disturbance of adjacent areas and surrounding surface and subsurface features. Normally, a rubber-tired backhoe or track excavator is used to dig to the approximate depth of the lines. But in urban, developed and heavy traffic areas, using a large piece of equipment (and even some smaller heavy equipment) can be problematic. Unloading heavy equipment, maneuvering in shoulders and traffic lanes, and working around other features makes it a difficult and costly method of exploration. When the approximate depth is reached, hand work with shovels is required to avoid a breach of the line. This process causes a large area to be disturbed, which can cause future problems with settlement in the areas directly surrounding the underground lines. Vacuum excavation avoids these difficulties by creating clean, dry potholes in the surface to expose utilities. SSMC uses a vacuum excavating unit made by Accurate Locating Inc. (Richmond, Va.) called the Utilivac VE75.
Commenting on the three-tiered tool system, DeMarsh says that "in our work nothing is obvious-it's all underground so you cannot see it to bid on it or know how deep it is or how hard it is going to be to find, horizontally or vertically. Common sense tells you to make one trip to a site, not three."
The New Improved ProcessAt the beginning of each project, SSMC crews perform extensive research to determine any possible underground utilities that exist in the work area. They first contact the appropriate one-call locator service to establish the types of lines and general locations. They then study as-built drawings that were created after construction was completed. While these initial investigations do provide some usable information, they can be problematic in two ways. Line location services mark what is believed to be the centerline of utility pipes or conduits. Both methods of research provide general horizontal position information, but do not include elevation or depth levels of the buried lines.
To overcome these obstacles, SSMC has developed utility locating techniques that are fast, efficient and highly mobile. A mid-sized flatbed truck with a utility bed contains all the equipment necessary for swift and productive mapping operations. The Utilivac VE75 System vacuum excavator rides at the rear where it is readily accessible and can be detached from the truck to dig remotely if necessary. Because of the risks involved in working in a vehicular traffic corridor, safety is stressed. For a linear project, like highway construction, locations are obtained by cross-section at set intervals, or if already designed, at the locations where existing utilities are in conflict with proposed construction.
Common utility designation methodologies are applied to horizontally locate and map all subsurface utilities. Conventional electronic line locating equipment is used for traceable utilities (either metallic in composition or having a trace wire placed in the ground with the pipe/cable allowing for location), and the Noggin SmartCart is used for all non-toneable (do not respond to conventional locating equipment) or untraceable lines.
The SmartCart with the Noggin, DVL and GPS+ equipment is rolled across the surface, perpendicular to the theoretical alignment of the underground lines. Carefully watching the DVL display, the operator sees intrusions as the surface is traversed. When the cart is directly above a visible line, a paint mark is sprayed on the ground and the position is recorded with the Topcon FC-100 field controller. The operator continues along the alignment, following the same procedure as other lines are observed.
Using vacuum excavation, SSMC's crew digs a small "test hole" (approximately 8" in diameter) directly down to the utility and safely removes all dirt and debris surrounding it. The crew then makes visual determinations regarding the type and condition of the line. The Topcon HiPer Pro GPS+ rover antenna is placed on a conventional rover staff and lowered to the top of the line. A point describing the precise horizontal and vertical position is collected on the FC-100 field computer.
After the location information is obtained, the test hole is backfilled with clean material and tamped back to density in one-foot lifts with pneumatic air tamps. The surface is then returned to its original condition-asphalt, concrete or dirt.
"By combining our expertise with the SmartCart and HiPer Pro equipment," DeMarsh says, "we have been able to more than triple our previous production rates no matter what the project might entail. Whether it is one simple locate or an entire roadway design/build, this equipment and our personnel have been a great asset to our clients."
The System in ActionThe Florida Department of Transportation (FDOT) awarded a design/build contract for widening Highway 411 in Leesburg, Fla., to handle increased traffic flow. To alleviate the growing congestion, the project was fast-tracked through approvals and funding. Normal map-design-relocate-build phases are now being done simultaneously. The current site under design is four miles in length, but the project will eventually extend across the city's limits. Extensive storm drainage work will be a major component of the project. For preliminary design purposes, FDOT contracted with SSMC to complete a topographic survey and excavate 127 test holes on the utilities along US 441.
The city of Leesburg owns almost all of the utilities within the project corridor including potable water, reclaimed water, wastewater, gas and electric. Florida Gas Transmission, Comcast Cable and Sprint round out the list of utility owners along the project. When the roadway design reached 60 percent of the planning stage, a copy of the proposed plans was sent to all utility companies involved for relocation planning purposes.
The city of Leesburg faced the problem of relocating all its utility systems within the corridor. To decrease the amount of excavation required and to enable all relocations to be placed within the established rights of way, a "common trench" method was chosen. The city contracted with SSMC to mark, map, verify and protect all existing utilities, and to lay out a proposed FDOT storm drainage system to determine potential conflicts. Multiple crews are working on these tasks daily. SSMC will also produce as-built surveys at 300-foot intervals when the relocations are completed. Following the completion of this first phase, work will commence on the next section of roadway.
The US 441 project has already presented many challenges to SSMC's crews. A citrus plant with numerous private utility lines is located along the right of way. There are no plans or as-built records for these installations, and most of them can't be located with conventional devices. Daily coordination of the multiple crews along with the activities of numerous subcontractors engaged in digging, drilling and boring operations has required positive and expeditious communication.
During the course of this project, SSMC was involved in a unique application of ground penetrating radar. A $10,000 directional drill head was lost 14' deep within an embankment when a shaft snapped during a bore. Using the Noggin and SmartCart, SSMC determined its location and then used vacuum excavation to expose it. A cable was hooked to the drill head, enabling it to be winched to the surface. The entire operation took only one day.
DeMarsh says that FDOT benefited from the "real-time exposure solution" by not having delay claims based on utility conflicts or utility owners being unable to relocate or protect their lines. The city of Leesburg, Sprint and Comcast all benefited by having all of their existing utilities mapped, protected during construction and new lines as-built.
The Next LevelNow that surveyors can obtain real-time utility data, how can it be used? For land development purposes, the significance is quite obvious. Through the surveyor's aid, projects can be designed with the confidence that conflicts between proposed and existing storm drains, sanitary sewers and building substructures will be identified and eliminated.
This real-time data can also be taken right out to the jobsite. A new development in machine control technology by Topcon puts real-time knowledge right where it's needed most-in the cab of an excavator. Topcon's 3Dxi indicate-only system enables the operator to actually see underground lines in plan, profile or section view on the screen of his control box. He can also visualize the planned depth of his trench and the movement of his bucket within the framework of the utility lines, giving him the ability to accurately control his digging operations.
New technologies and products for the surveying and construction industries are being developed at a rapidly increasing rate. It takes progressive companies like Southeastern Surveying and Mapping Company to see the possibilities for practical applications that will benefit their clients and the public.