Ingenious surveying helps keep an oversized crane safe and on schedule and a small firm profitable.

Surveyors monitored the crane from below as it was used to lift the twin derricks and drilling deck. At 450,000 pounds, this was the heaviest lift of the project, and topped out at more than 300 feet.

Nathan Weber is an early adopter. He’s keenly interested in new technologies and eager to put them to work. For Weber’s company—Diamond Design and Land Surveying in Murray, Utah—the use of new technology has kept things hopping through the economic downturn. But that’s not just due to the fact that the firm owns the latest and greatest instruments. A big part of Diamond’s success has been the innovative ways in which it applies the new tools for its clients.

During the last few years, Diamond has diversified from its focus on land surveying to include work on industrial sites including factories, mines, and refineries. The firm carries numerous safety certifications, enabling it to work on almost any industrial facility in the state. And Diamond’s array of surveying systems—robotic total stations, 3D scanner, and advanced spatial imaging and GPS instruments—provides the capability to handle surveying for industrial customers as well as cadastral and land development projects.

One of Diamond’s industrial clients is the Chevron Refinery in Davis County near Salt Lake City. Diamond has worked at the plant for more than five years and completed numerous construction and engineering surveys for that client. In the summer of 2008, Chevron began a maintenance project on a coking unit in the refinery. Two cylindrical coking drums needed to be removed and replaced. Each drum was 93 feet tall, 19 feet in diameter, and weighed 319,000 pounds. Before the drums could be removed, two derricks and other superstructure had to be lifted from the tops of the coking drums. The tops of the derricks were about 300 feet above the ground. To complicate matters, the coking unit was surrounded by the tanks, pipes, and machinery of the active refinery.

Mark Vaughn, Chevron’s project manager for the coking unit work, summed it up: "Everything we do revolves around safety. We needed to lift some very big, very heavy items in a limited work area hemmed in by flammable materials."

The project called for an enormous crane, intensive planning, and innovative surveying.

The crane selected for the project was a Lampson TransiLift 1200 (LTL 1200), manufactured by Lampson International of Kennewick, Wash. The LTL 1200 sat on two crawlers, 36 feet wide and 6 feet high. The forward crawler supported the boom attachment while the rear crawler held the counterweights. A platform between the two crawlers held the crane’s machinery, cable spools, and operator’s cabin. The total length of the assembled crawlers was about 145 feet. The crane’s boom was 460 feet long, and the combined weight of the crawlers, booms, machinery, and counterweights was about 4 million pounds.

Carried in pieces on dozens of flatbed semi-trailers, the crane began to arrive on site in July 2008. The project plan called for the crane to be staged on assembly pads and then "walked" about one-fourth mile to a construction pad next to the coking unit. Constructed of highly compacted road base with an asphalt overlay, the assembly pad needed to support the weight of the crane and keep it stable during the assembly and test phases. In addition to supporting the main crane, the assembly pad also had to accommodate several smaller cranes needed to assemble the behemoth.

Diamond’s surveying work on the assembly pad was the preliminary step to the larger, more complex project. "Chevron asked us to do the topographic survey and design for the assembly pad," Weber said. "We did some conventional earthwork construction surveying and laid in control for the next phases."

Diamond also surveyed the route that the crane would take when moving to the construction pad. The team used a 3D scanner to verify that the road could handle the weight and that there was sufficient space to allow the crane to pass by. In one location, there was less than 2 feet of clearance for the gigantic, difficult-to-maneuver machine. And a more difficult problem awaited them at the construction pad.

Nathan Weber, L.S., (right) and Lucas Blake monitored the huge crane with a Trimble VX Spatial Station as it moved to the construction pad. Two Trimble MultiTrack targets are visible over their shoulders.

Removing risk
A crane the size of the LTL 1200 must have a stable foundation. This depends heavily on the soils at the project site. In many projects, the large cranes are placed on mats made of multiple layers of large hardwood timbers. But the soils at the Chevron site were not suitable for this approach, even with large timber mats. "The bearing capacity of the ground was adequate, but well below what is commonly seen," said David Duerr, an engineering consultant on the project. "It was the first time I had seen such a large crane set up on that type of soil."

To provide the needed stability, Chevron engineers designed a concrete mat that they described as analogous to a catamaran sailboat. On a catamaran, forces on the sail and mast are moved to the sides of the vessel and distributed along the length of the hulls. The result is high stability and excellent control. The Chevron mat was approximately 70 feet wide and 120 feet long. The mat was 2 feet thick in the center and 3 feet thick around the edges. The pad was reinforced with 28 miles of #9 rebar and contained about 1,200 cubic yards of concrete. The thick edges of the pad functioned like catamaran hulls to distribute the weight.

Before the crane could be moved to the construction pad, the engineers needed to monitor the mat for settlement and to evaluate how the mat would behave under the immense loads. To accomplish this, Weber installed a series of markers in the mat and used a Trimble DiNi Digital Level to establish control for monitoring measurements on the concrete mat. The Lampson team loaded the crane’s rear crawler with more than 2 million pounds of counterweights and walked it onto the construction pad. To test the pad, the crawler was parked at different locations on the pad over a few days, and then walked back to the assembly area.

Crews then placed 40 large tanks filled with water on the concrete pad to induce settlement and compaction. The surveyors took digital level observations while the loaded crawler was on the pad and twice per day for three weeks while the pad was loaded with the water tanks. The Trimble DiNi Digital Level provided measurements to 0.001 foot, and the team used the precise data to quantify the pad’s settlement and behavior under heavy loads. To ensure accuracy, Weber kept the measured lines short, usually less than 75 feet. The surveyors avoided the heat of the day by taking measurements in early morning and again in the evening. As the settling slowed, the surveyors reduced the measurement interval to once per day until the Chevron engineers were confident that the pad was solid and would not tilt or buckle under the weight of the crane. The soil problem was solved.

With the tests completed, it was time for the crane—now fully assembled—to return to the construction pad. The crane specifications state that during walks and lifts the crane should be kept level to within 3/4 inch (0.06 foot) across the 36-foot width of the crawler. Traditionally, this is done with a simple fluid level that is visible to the operator and others on the ground. Weber had a better idea.

He proposed to use his Trimble VX Spatial Station to monitor the crane continuously and provide precise numerical information about any tilt or settlement of the crane or the ground beneath it. The surveyors mounted two Trimble MultiTrack targets onto the front of the forward crawler, about 16 feet apart. For the lifts and walks, Weber used a Trimble S6 total station to supplement his Trimble VX. Each instrument was connected to a Trimble TSC2 controller running Trimble Survey Controller software.

For the measurements, the two instruments were set up side by side, each with its own operator. At each setup, the Diamond team measured the height of one instrument and shot to several targets around the site. The height of the second instrument was determined by measuring to the targets, and then double-checked to confirm that the two instruments were exactly on the same vertical datum. Whenever the crane was walking or making a lift, two Diamond surveyors continuously measured the two targets and compared readings. Ideally, the elevation of the two targets would stay the same. If they noted a difference of more than 0.015 foot, then they alerted the operators.

Because the crane had to stop whenever the survey crews were moving from one setup point to the next, it was essential to do the setup and calibration procedure quickly. "Accurate and fast are not mutually exclusive in some cases," said Weber. "The speed of the Trimble system allowed us to move quickly and minimize the downtime for the machines." Weber also noted that the cable-free communications between the Trimble instruments and data collectors was important. If necessary, they could operate the instruments remotely and still provide precise data on the crane’s behavior.

As the crane went to work lifting the enormous loads, the surveyors’ work intensified. Starting 30 minutes prior to each lift, they measured the targets every 30 seconds to establish baseline data. The monitoring continued throughout the lift and for an additional 30 minutes after the lift was completed.

The heavy lifts seemed to go in slow motion, allowing the teams to see how loads on the crane affected the concrete mat. Sometimes the load needed to be held for hours, and the continuous information about the crane provided by the Trimble system was important. Any tilt or motion could be detected immediately. The surveyors could tell the contractors if things were moving, and by how much. There were a lot of 18-hour days, Weber noted. "We needed to stay ahead of the contractor crews and keep things on schedule. In spite of the huge size and complexity of the project, things ran smoothly."

The Diamond surveyors used the Trimble TSC2 controller to record the measurements for future analysis by the Chevron engineers. Vaughn said that the concrete mat did its job. "We saw some vertical motion as the loads on the crane changed, which was expected. But there was virtually no tilting, and that was our main concern. The information we got from the surveyors prevented problems and removed risk."

Consultant Duerr was also pleased. "The presence of the surveyors added a valuable layer of safety and precision to the work," he said. "They provided another set of eyes to keep things going as expected." By mid-October, the heavy lifts were completed and the crane had moved back to the assembly pad to be disassembled and shipped to its next project.

Diamond Design and Land Surveying’s Nathan Weber, L.S., (left) and Lucas Blake compare measurements to the two targets on the crane. The surveyors took readings every 30 seconds during the lifts.

A flexible future
Weber was happy to share what he learned on the project. "Take care of the important things first," he said. "We made sure our control was accurate and stable, and then looked for other ways to apply our expertise to the project. Without the Trimble VX, Trimble S6, and Trimble DiNi, this project could not have turned out as well as it did."

Weber envisions keeping his company small and agile because it allows him to make quick decisions to purchase advanced technology. He plans to use the Trimble VX Spatial Station to provide geo-referenced, orthorectified images for cadastral, industrial, and architectural clients. And he sees the instrument’s video capability as important for the firm’s frequent one-person surveys. "Flexibility is the key in today’s market," he concluded, "and our investment in technology has paid off. It’s kept us working and profitable."


John Stenmark, L.S., is a writer and consultant working in the AEC and technical industries. He has more than 20 years of experience in applying advanced technology to surveying and related disciplines.