A 3.000Mb PDF of this article as it appeared in the magazine—complete with images—is available by clicking HERE
It was a pre-dawn routine that became familiar over the course of the six-month project to place steel transmission line piles into Nueces Bay. Sometimes fog had moved in during the night and our headlights barely cut a 100-foot path ahead. Switching to ATVs at the staging area, we would drive another 20-30 minutes to the base station site. Our first task was to check the GPS control stations along the shore of Nueces Bay. A second team would set up conventional survey equipment and run control checks on an area parallel to the Nueces Bay work site. With the GPS equipment up and running we headed to the dock and jumped into our boat. Some mornings the temperatures would drop to near freezing and the winds would blow at a constant 25-35mph. Typically, the ride took about 25-30 minutes, but there were many days when strong tides and heavy swells would pound on us, making progress slow. When we would finally get to the work platform, we would be soaked; even our cold weather suits didn’t help. We were now two hours into a normal 16-18 hour day, as the construction team warmed up their equipment and the diesel engines came to life . . .
Nueces Bay was but a segment of a transmission line improvement project undertaken by American Electric Power (AE P), today called AEP Texas Central Company (TCC), in Corpus Christi, Texas. Starting in 1999, the San Antonio firm of CDS/Muery Services was contracted to provide support for the entire project, which included 12 major electrical lines covering more than 75 linear miles of electrical circuit. The goal was to upgrade and strengthen the South Texas electrical grid. Along with rebuilding existing 69kV, 138kV and 345kV lines, the three-year project included placing more than 40 miles of new 138kV electrical circuits. The main part of the project was between the Lon C. Hill Power Plant and the Nueces Bay Power Plant, with more than a dozen substations tapped into the primary lines (see map). The project encompassed rural areas, downtown subdivisions, industrial and refinery areas; it also passed over the Corpus Christi ship channel and through the waters of Nueces Bay.
Setting Control
CDS was involved in all phases of the project, from planning to final completion. After line route plans, rights-of-way, tax records, deeds and all environmental issues were resolved, CDS was ready to start surveying. Utilizing Trimble Global Positioning System (GPS) technology and aerial photography, CDS set a GPS control network over the entire area. The network included 25-30 points over an area of 20 square miles, each no more than three miles apart. The points were tied into a variety of National Geodetic Services (NGS) published control monuments. From the primary GPS network, CDS set more than 800 control points for the entire project, establishing a secondary network for each project area.
After the main control network was in place, CDS began an intensive topographic and boundary survey. Several crews in different areas collected more than 75,000 points for everything from found boundary monumentation, underground pipelines, roads, distribution lines, wells, buildings and fences to line heights of anything close to the proposed route. Several local and state agencies conducted detailed environmental studies in Nueces Bay and provided the information to CDS for integration into the main information database. CDS generated a detailed Digital Terrain Model (DTM) consisting of more than seven million points and more than 30,000 breaklines from aerial photogrammetry, hydrographic data, and conventional and GPS ground surveys. Once the data was compiled, CDS choose proposed structure locations along the proposed routes within the design file.
Constructing the Line
After the line design was completed, CDS staked each structure location. In the waters of Nueces Bay crews used 3"x10′ PVC piping to mark the center of each structure location, the limits of the oyster reefs, seagrass and areas to be dredged. Markers were color coded to match coding on maps generated by CDS and provided to the contractors and project staff. Utilizing Trimble GPS we were able to set all markers and navigation buoys before the start of the water construction phase. In shallow water, crews sometimes waded out from shore with a GPS pack and set markers in only a few feet of water. CDS generated a centerline for the main navigational corridor and provided the data to the marine contractors to upload routes into their navigation equipment. The uploaded routes and navigational markers gave the contractors a clear and concise corridor to navigate to and from the job site safely. CDS crews returned to the water and removed all the navigational aides after the marine contractor and related traffic was finished.
For the Nueces Bay segment, CDS set more than 100 additional control points along the shoreline. Each control point was placed on the bisecting angle for each structure located in the Bay; this allowed crews to quickly verify the contractors’ location and the pile-driving operation. Because many points were set in sand, crews constantly monitored the key points for shifting earth conditions and poor soils. CDS mainly used GPS systems for the job, but the team also had backup systems. For example, while surveying across Nueces Bay, crew members had to check against errors caused by signal reflections from the water, also known as multipathing. Crews also constantly monitored the base station to make sure correct positioning was being relayed to the rover units. One team was solely responsible for running conventional equipment along the shoreline and running the check and balance processes CDS had established, maintaining accuracy while driving each pile into Nueces Bay. All contingency or backup plans were preplanned before reaching the site. With 95 poles in the water and another 40 on land that went through marsh and swamp, the team needed failsafe measures to backup all systems and processes. For the six months CDS was at the Bay, crews were on site 24/7. With each pile weighing approximately 50,000 pounds, standing 92-120 feet high, and measuring five to eight feet in diameter, mistakes would have been irreversible and lost time irreplaceable. The pile driving operation needed to stay on schedule as the contractor erecting the transmission line followed closely behind us.
Once the 50-foot-tall steel framework was placed and anchored to the sea bottom over the centerline mark, the CDS surveyor would don a fullb ody fall-arresting harness along with Trimble RTK GPS 5800 equipment. Putting the gear on was a serious matter; if the harness was not properly worn, one slip could mean falling 40 feet through the steel framework to the water below. With a strong sea breeze (or storm winds and rain) and a 50,000-lb pile being placed down through the framework, crew members had to focus on their task while maintaining complete awareness of all operations going on around them. The steel beams we walked on and worked from were just 12 inches wide. GPS and sometimes conventional positions had to be marked on all four sides of the outer steel frame. This allowed the inner frame bracing to be bolted onto the outer framing and hold the pile on the correct angle and axis during the driving operation. C D S utilized handheld computers loaded with our database; the graphical displays showed coordinate values that enabled crews to immediately cross-check and verify the GPS positioning values for the layout of each pile. As this was one of the most hazardous parts of the project for the survey crews, crew members took turns laying out each pile so no one b ecame too fatigued; CDS credits the success and
safety of this operation to each crew member and the detailed safety processes in place.
Accessing the Channel
As the pile driving operation transitioned from Nueces Bay to the north side of the ship channel, CDS surveyed the viable access roads and levees in order to find a safe way to get the heavy construction equipment where it was needed. Utilizing the tracking feature of the Trimble RTK G PS 5800 system, crews mounted the receiver onto an ATV and collected thousands of points in just one afternoon. The data provided the outlines of the existing dirt roads and levees in and around the transmission line area. Detailed topographic data was also collected along both sides of the ship channel. Next, the plan was made to barge the heavy equipment, cranes, piles and transmission poles up the Corpus Christi ship channel to the temporary dock that was constructed at the project site.
Grading and slope information was critical to the success of driving a large crane off the barge and up the levee system to the project location. The existing levees were dozed down to form a road and bridges to each structure location. The topographic data collected allowed the contractor to compute volume reports, as well as plan and move vast amounts of earth into each location. Once construction was complete, the earth was moved back to reform the levees and reconstruct the existing features. It is hard to appreciate this operation without knowing what happens when heavy equipment is moved through water-soaked sand; even 4×4 survey trucks got stuck if crews wandered a few feet off the path. CDS utilized ATVs for most of this work area and kept 4×4 trucks at a solid staging area. Before the road system was constructed ATVs often had to move in pairs, one behind the other. The lead vehicle would find all the soft spots and on several occasions had to be pulled out by the trailing vehicle.
Refined Surveying
Part of the transmission line work went through the middle of Corpus Christi’s main refinery area, offering new challenges and unique approaches to surveying features and construction techniques. An intensive topographic survey had to be completed during the design survey phase of this project. Unlike crossing the field or water segments, which had few aboveground obstructions, the refinery areas provided many details needing to be factored into the design: pipe rack crossings, blow-off stacks, guy downs, refinery buildings, tanks and complex areas of fencing and equipment. One of the greatest challenges of this portion of the project was to explore below the surface of the ground; teams needed to find areas to place foundations for transmission poles without jeopardizing piping, telephone lines, control cables and other underground obstructions. CDS had to explore these areas without damaging any underground features or posing any safety risks to the personnel or equipment.
Using a hydro-excavation technique, a utility location contractor under CDS direction cut a four-inch-wide trench as deep as possible at key locations. The high-pressure water stream could cut through the ground without damag ing or providing any safety risks to personnel and underground utilities. The hydro-cutting action was designed at the end of a vacuum hose used to cut and simultaneously suck the ground and water into a storage tank. This process was a huge success, enabling us to find the exact location of each structure’s foundation and determine any size restrictions. Each trench was surveyed, and the results documented and reported to the engineer for design and placement. This exploration provided valuable information for the design and ultimately enabled each foundation to be constructed safely.
As spring approached, the project came together. With more than six primary companies involved, an on-site work force of 75+ personnel and a team of support staff numbering well over 100, the project was a testament to successful teamwork and collaboration. As the sun set, crews took their final ride along the newly constructed transmission line and electrical current started running through the lines. The CDS team remains proud to have been involved in such a challenging and rewarding project.
Travis Lung is a Project Manager/ CADD Manager at CDS/Muery Services in San Antonio, Texas.
A 3.000Mb PDF of this article as it appeared in the magazine—complete with images—is available by clicking HERE