Enlarge this picture An example of a DTM that did not correctly feather the intersection of a new road into the old road.

There has been a lot of discussion about the requirement in many states to have a professional engineer or licensed surveyor certify 3D data prep models for GPS machine control and related construction work. Inevitably, events are introduced onsite that render a license completely ineffective and which a professional engineer (PE) or professional licensed surveyor (PLS) cannot resolve. Such events often tend to involve human error. In this column I will share some of the stories about these errors and the lessons learned from them.

Scenario #1: Communication

On a fast-track project that was in operation 24/7 and that included heavy use of GPS machine control equipment, the contractor had a couple of base stations established onsite. Everything was swimming along. As the shift supervisor headed home one night, he received a phone call from a crew member. “Hey boss,” he heard, “is it a bad thing if we knocked over the base station?” Immediately, the supervisor began to think of the ramifications of this question, and a swirl of possible consequences floated through his mind, followed by potential penalties and other negatives that could spoil an otherwise successful day in the field. Before the supervisor finished contemplating the possibilities, the crew member proudly said, “Don’t worry, chief, we put it back up!”

At that moment, the supervisor realized that this was much worse than he had originally thought. He responded with the best question one could ask in this situation: “Exactly when did all this happen?” The answer quickly came: “About two weeks ago.” At this point the supervisor’s heart skipped a beat, again weighing the outcome of these actions. Most of the work in the past two weeks had been controlled using another base station. Although the base station in question was established onsite, work had not progressed to that area of the site yet. The supervisor learned that the base station had been knocked over during some clearing and grubbing by a low-level employee who was devastated by his mistake. He set it back up and waited several days before mentioning it to someone else, who realized the importance of the comment and passed it up the chain of command.

Lesson Learned: A good relationship with staff members will enhance communication and help to identify challenges early on. Issues that seem insignificant to some may be critical to the operation of the project as a whole, so a certain level of education needs to be imparted to all workers on a site--even to those you never imagined would need to know anything about the technology and equipment being used.

Scenario #2: Teamwork

A contractor tasked with grade checking had a GPS rover and walked the site checking elevations to ensure that the heavy iron hit its mark. Although there was nothing peculiar about how this rover antenna was supposed to be affixed to the rod, this worker did not know how to correctly attach the GPS unit. As a result, the antenna was connected to the rod in a flimsy fashion and quivered significantly. As the worker traversed the site carrying the rod, the antenna wobbled around at the top of the rod and hit his hard hat with each step he took. This went on for about a half hour until a fellow worker noticed that a smacking noise periodically occurred whenever his team member was walking. So he ran over to his team member and stopped him to disassemble the antenna and reattach it correctly. He then reshot the data in the area that was compromised by faulty readings.

Lesson Learned: Teamwork is essential for catching problems onsite. To ensure that teamwork is effective, basic training is critical for all members of the construction crew, including grade checkers.

Scenario #3: Safety

As a supervisor was heading home after a long day onsite, his cell phone rang. He answered it immediately assuming it was just a coworker checking on something trivial. But the caller on the other end was breathlessly repeating, “The base station is on fire, the base station is on fire!” The supervisor recognized the severity of the issue and tried to calm the employee.

After a minute, the worker calmed down enough to say that the base station was sparking and smoking. The supervisor said, “Pull the power and disconnect it from the equipment.” In the background, the supervisor heard workers yelling, “Pull the power! Disconnect it!” This was followed by “I can’t--it’s stuck!” Then there was a pause. Finally, the caller came back online and said, “Um, the power was forced into the socket on the base station backward and it looks like it short-circuited the equipment.” The supervisor could only shake his head and conclude that this would not be covered by the warranty.

Lesson Learned: Safety classes for all staff are imperative--even instruction on the most mundane of tasks should be conducted.

Scenario #4: Awareness

Running a dozer with a new GPS and robotics system installed, an operator was pushing earth and backed up toward the crest of a hill. As he was backing up, he lifted his blade at the same time that the center of gravity hit the top of the crest. The momentum of the blade, compounded with the velocity of the dozer approaching the top of the hill, flipped the entire bulldozer 180 degrees down the other side of the hill. Of course, the new GPS antenna system was destroyed.

Lesson Learned: Be aware of your environment, especially when backing up.

Scenario #5: Trust the Machine

As a fairly new operator using GPS machine control to grade an intersection moved his dozer forward, an odd amount of blade chatter was evident to him. Even though he was new, he knew something didn’t seem right--harmonic motion was causing the entire machine to rock. He called his supervisor and suggested that something was wrong with the machine, perhaps the blade bushings or the hydraulics.

To the supervisor’s credit, he dropped what he was doing and came right out to assist. The supervisor couldn’t find anything wrong with the equipment or hardware and began to question the data set. They then called the technical support department of the data model software company. After sending the data set in for review, it was immediately obvious that the consultant had tied a new roadway into an existing roadway that was significantly beaten up by age and traffic. The result was an intersection that had many DTM triangles in it, each reacting to the undulating grades of the existing road (see the figure on page 58). The consultant identified that the new road should have been feathered into the existing road rather than slammed up to match the existing fluctuations. The data was rebuilt with a feathering solution, and the model worked fine from then on. The blade stopped chirping, the cab stopped rocking and the data prep company learned a lesson.

Lesson Learned: Trust your machine. It talks to you.

Scenario #6: Do a Headcount

On one particular project, the field crew needed someone to fill a non-technical surveying role. They grabbed the “print room guy,” a cooperative fellow who was not skilled in surveying. He was asked to climb down into a manhole and capture the inverts of the various features, pipe inverts and bottom of structure. He did it all with a positive attitude. Once the data was recorded, the party chief yelled, “OK, let’s move to the next manhole.” As they packed up their gear and moved about 300 feet forward and set up again, they noticed that the print room guy was not among them. They glanced around and called out to him, but he was nowhere to be found. Everyone was on the verge of accusing him of desertion when one of the field crew members popped the manhole cover. Lo and behold, the print room guy was standing at the bottom with a big smile on his face. “What took you so long?” was his first question.

Lesson Learned: Take nothing--or no one--for granted.

A common thread in all of these scenarios is that training is absolutely essential for everyone involved in the use of machine control technology on the construction site. The purpose of highlighting these anecdotes here is to encourage all crew members to keep up their guard, stay vigilant and support their teammates.