Innovation Leads to Increased Production

In May of 1999, the Rose Group was requested to provide professional surveying services for a unique project that required extreme time restraints. The project involved the installation of a new berm atop an existing dike for a dredging containment area at Eagle Island in Wilmington, North Carolina. Eagle Island lies opposite the Port of Wilmington between the Cape Fear and Brunswick Rivers and is home to the Battleship USS North Carolina Memorial. In order to maximize the depth of the harbor area for increased shipping, the Corps of Engineers planned to dredge the harbor and pump the dredged material into an existing cell or containment area on Eagle Island (there are presently three existing cells on the island). Once in the containment area, the solid material would settle with the water leaching out. This area of North Carolina poses some interesting challenges not the least of which is that Wilmington is known as landfall for Hurricane Alley and the time period of this project was during prime hurricane season. In addition, our crew would face the possibility of alligators, snakes, unstable ground, and enough swarms of mosquitoes to compromise the local weather radar. Due to environmental concerns, the window of opportunity for completing the project was extremely limited. The berm had to be completed within 90 days from authorization and the dredging was scheduled to begin immediately following this deadline. With liquidated damages in excess of $800 per day, the contractor was concerned about the need to complete this project in a timely manner.

Primary Duties
The Rose Group's area of responsibility was to provide on site horizontal and vertical control, determine the topography of the existing dike before any construction activity, lay out the offset line to the center of the new berm, continue with quantity calculations as the work progressed for each payment schedule, and ultimately the final as-built survey. The length of the berm was over 15,000 feet and the alignment would need to be staked at all PIs, PCs, PTs and each fifty-foot station. The project control points provided were brass disks set by the Corp of Engineers in the concrete bulkhead, one foot in from the outside edge of the pier on the east side of the Cape Fear River.

Stages of Planning
At our initial "kick off" planning session our team discussed procedures and potential problems. In order to keep the project on schedule, we needed to devise a method to perform our work as quickly as possible without jeopardizing accuracy. The Rose Group's present GPS System consists of two Trimble 4700 Series Receivers and one 4800 Series Receiver, all three of which are 9 channel dual frequency, a Pacific Crest 35 watt Base station and a handheld channel scanner. Since the receiver radios are "voice priority," our crews found on previous projects that in areas of high voice communication, radio traffic (as was the case in the Port area) would break the GPS radio link signal compromising the consistency of the continuous data being collected. This problem could have been alleviated by increasing the frequency of the collected information (by having short time intervals or distances when the data is collected) or by securing a clear radio channel. The crew now scans all available frequencies upon reaching the job site for the channel with the least or no radio traffic. The system is then set to work on the clear channel with no interruption. In situations when there is still a question as to a possible break in the radio signal, the system can be set with the interval between data acquisition closer together. This $100 scanner has saved us from lost time, lost data, and much aggravation.
Since the island was mainly grass and low scrub trees, utilizing the GPS system for the data acquisition and layout was the obvious choice. Still, we needed to put a procedure in place that would expedite the project for at least the initial phase, as the contractor could not do any work until the existing berm was completely surveyed. Walking the entire length of the berm to acquire the topography would have taken a week or more for one crew and we did not have the luxury to send multiple crews for any significant length of time. Fortunately, in today's technological environment we are only limited by our imagination.
We decided to utilize an ATV with one of the Trimble GPS rovers mounted on it to acquire data via "Real Time Continuous Topo." Being experienced in the use of GPS in the conventional sense, we had previous success using the system on a four-wheel drive vehicle, but it was yet untried on an ATV. With regard to the staking of the horizontal alignment, walking with the GPS unit could not be avoided.
The next problem to be tackled was accessing the control points at the pier and maintaining the integrity of the control set on the island during the project. The Corps of Engineers indicated that the ground on the island was unstable and maintaining the integrity of any control would be a problem. Therefore, the contractor opted to set an "I" beam pile driven to refusal as the on site control point. Once this was set it would need to be periodically verified to the project control on the pier. The vertical alignment of the laser that would control the earth-moving with the grading equipment was to be set from this control point with the horizontal alignment for the new berm provided from the staking. All field data was to be mapped and quantity computations performed in AutoCAD v.14 and Softdesk v.8. Upon completion of the initial survey, a digital terrain model of the existing ground surface would be created and as each new survey of a completed section of the berm was finalized, a respective DTM would then be added to the file. The quantities could then be computed by comparing the difference in volume between the two surfaces using Softdesk's Earthworks Module.

Potential Problem
It became clear that if a ship was in port, accessing the control points would be out of the question. A ship, having docked within close range of the GPS unit, would cause multipath to compromise the signal and the data. The contractor acquired permission for The Rose Group to set a control point on the east side of the river in an area that would be accessible as needed, yet protected from being disturbed after working hours for the duration of the project. The Corps of Engineers gave us their blessing on the use of the ATV and we were ready to begin.

Attention to Detail
We began the project on the fourth of June with one man on an ATV and two men staking. Since the contractor had not yet set the "I" beam or acquired permission for the remote point to be set, our plan was to get initial control points established on the island for the first phase. The proximity of the overhead cranes at the port caused some concern so it was decided to transfer the control conventionally. This led to a lesson learned that we all need to remember, and that is to always check your field computations (Survey Class 101). In our rush to get started, a computation was not checked in the field and then overlooked in the office, causing a bust in our initial vertical control of about 0.7 tenths of a foot. Fortunately, it was discovered without causing any serious problems.
Once the control was on the island, the ATV was fired up and the topographic survey began. At the same time the two-man crew began staking the offset points for the horizontal alignment. Since we needed to have sufficient information to create the DTM, the ATV made numerous passes on the dike along the top outside edge, the top between the edges, the top inside edge, and the bottom inside edge. This was all completed in the field in one day. The other crew completed the staking of approximately one half of the alignment in two days. Once back in the office, the GPS data was reviewed by our land surveyor in charge of GPS Services in about three hours and the mapping/computations process was begun. Upon completion of the DTM, cross sections were cut at every fifty feet and digitally sent to the Corps of Engineers' Wilmington Office. The earth-moving operation began in earnest as soon as the initial survey was completed. Under the direction of the contractor we would need to revisit the site weekly in order to determine the quantities of the newly installed berm and to continue staking or resetting points destroyed by construction. These return trips brought to light another challenge when working on Eagle Island—dust so thick we could not see five feet in front of us. With the exception of the safety concerns related to all of the earth-moving equipment in operation, the use of GPS eliminated any down time and the staking stayed on schedule. Twice in August we were hit by hurricanes and twice we were directed by the contractor "to do whatever is necessary to record the amount of material in place." Both times we surveyed the site via ATV/GPS, all completed in less than a day. The contractor was able to complete the project under schedule even with the weather delays.

Interesting Findings
What we discovered from this project is that the use of the ATV and the GPS has dramatically lowered the time necessary to complete the field portion of this type of survey. It did not, however, create a reduction in the amount of office time required for the volume reductions and computations. In fact it gave a disproportionate comparison of field to office time than we were used to seeing. This had to be addressed when the client's billing was produced. We realize that this particular project lent itself to the use of this equipment and not all projects would benefit from these devices. We continue to use the system and have found that with the right personnel in the field and the use of a laptop computer we can reduce, analyze, and confirm the coverage in the field before returning to the office. Since that survey, we have had the opportunity to produce a topographic survey of seventy plus acres using the same methods. On this project we needed to lay out the limits of the area to be surveyed before acquiring the topographic information. This site was completely open with only some hillocks and scrub brush to impede the use of the ATV. A two-man crew, one on the ATV and one walking with a rover completed the survey in less than eight hours. During the one-hour return trip, the data was reduced and ready for mapping on the crew's arrival back at the office. Again this site also lent itself to the success of this procedure.
Our department has realized that technology is a wonderful thing, but every new advancement may not necessarily work best for every project. So, we continue to seek out the best procedures that technology has to offer as we continue to professionally provide for our clients' continuing needs and expectations.

Raymond B. Dawber is a Professional Land Surveyor/Project Manager for The Rose Group in Fayetteville and Raleigh, North Carolina. He is presently the Group Leader in their Raleigh Office.

The author would like to thank Jimmy Holland Jr., LS, as The Rose Group GPS Manager, and Chris Pusey, LSIT, who was instrumental in maintaining the quality of the field operations and computations on the project.

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