GPS System Makes The Grade On Irregular Lake Bed Project

By Larry Trojack | September 28, 2010

One of the inherent strengths of today's newer GPS systems for construction equipment is their ability to present the operator with an in-cabdisplay of the terrain — even when that terrain is under water. That ability alone can shave significant time off a project. Couple that advantage, however, with a reduced reliance on staking and checking; elimination of the risk of over-excavating and an over all improvement in quality; and that system becomes invaluable. On a recent subdivision project which called for creation of a pair of man-made lakes, an uneven lake bottom — deliberately designed to provide for fish habitat — would have stymied most grading firms. For Omaha-based JAM Grading, equipping their excavator with a Topcon GPS+system made it another day at the office.

The Shadow Lake development in Papillion is the latest addition to what is becoming one of the most prestigious — and fastest-growing — suburbs of Omaha. When complete, the 400-acre site will feature 700 mid- to upper-bracket homes and an amenity fairly uncommon to the Nebraska landscape: a 47-acre lake. According to Jon Maloney, project superintendent for JAM Grading, Trucking & Demolition, the firm handling grading for the entire project, that water feature offered its share of challenges.

"The horseshoe-shaped lake is actually two separate digs — one 11 acres, the other 36 acres — which represent removal of about 400,000 yards of material. There were a number of issues that challenged us throughout the course of the project, but none more so than the water table. Despite ahydrologist's report that said it shouldn't happen, water started coming in 5 feet before we hit our designated lake bottom. So we dug a trench to cut off the ground water, pumped out the area and let the ground firm up enough for us to resume bringing in equipment."

Lake depths, according to Maloney, will vary, but will generally be 18 feet to 20 feet deep in the larger Shadow Lake reservoir side and 24 feet in the smaller Midlands reservoir side.

"The Midlands side is designed deeper to allow for a 10-foot accumulation of silt from runoff over the next 20 years. However, if the area continues to develop the way it has, the runoff won't be anywhere near that projected depth."

With a 21-year history under its belt, site development is nothing new to JAM Grading. Even the opportunity to do some lake creation was well within its job description. Where things got murky (literally, in some cases) was in the special contours of the lake bed at Shadow Lake.

"In many areas, the lake bed is anything but flat," says Maloney. "It undulates with bowls, humps and ridges that are designed to be enticing habitats for fish when the lake is filled. While that's a great, environmentally sound idea, it presented a whole new set of grading challenges for us. Based on previous experience with this technology, I made the decision early on to purchase a GPS system; it proved to be one of the best decisions we could have made."

Despite their efforts to keep things dry, Maloney says there were many cases in which the lake bottom was still under water making it impossible to check grade in a traditional manner.

"That was also the case with every one of the bowls and depressions in the lake bottom," he says. "Using the Topcon 3DXi, however, our operator simply looked at the profile on his cab display and saw the whole picture: what he had done, what he was currently doing and what he had yet to do. Based on that, it was simply a matter of digging down to grade; a job which could have been a real headache was suddenly easy and accurate."

The system in place at JAM Grading, a 3DXi GPS+ system from Topcon Positioning Systems (Livermore, Calif.), brings excavator operators the same grade control benefits available for years to users of dozers and scrapers. According to the Todd Bechtel, vice president of Omaha-based DK&B Construction Specialties, which initially rented the system to JAM, the 3DXi features 360-degree CAN-based tilt sensors which continually measure angles from the excavator's cab, boom, stick, and bucket.

"This allows the operator to make a precise cut every time regardless of what angle the machine is at. If he is sitting on a 4-percent grade, for example, and puts the stick out, the unit has already factored in that grade and displays the appropriate terrain shot to him — in real time — on the cab-mounted GX-60 control box/display. That display can prove valuable in a number of ways, including allowing operators to accurately position their machine over a utility centerline, and as an aid in steering indication. I might add that, although the 3Dxi is the most sophisticated system available today, our customers find it to be very user-friendly. So from a support standpoint, we have the best of both worlds."

Bechtel adds that, because GPS-based systems are largely software-driven, changes and upgrades are fast and easy. "Topcon is excellent in that regard as well," he says. "They are very responsive to feedback from the field and make any resultant upgrades free to their customers, which really makes a difference. JAM Grading first took the 3DXi as a 120-day rental and had such success with it that after nine months they bought it outright."

Ironically, a good part of the reason for JAM's extended use of the 3DXi was the result of its success. According to Jon Maloney, the ease with which they were able to make accurate cuts kept things moving along so well that additional on-site work — add-ons, he called them — presented themselves.

"There's no doubt that the accuracy of the GPS shaved time off this project — in our case, I'd say we saved weeks. In this business, both time and money can be lost through over-excavating and on a site comparable to what we were doing at Shadow Lake, just over digging by 1 inch can result in unnecessarily moving 5,000 yards of material. Given that our expenses out there were about $12,500 a day, it's easy to see how that can all add up. Using conventional methods, it is possible to waste $50,000 to $60,000 in a hole that size. Because excavation is no longer guess work, that risk has been eliminated with the Topcon system."

The add-ons JAM "earned" included a number of on-site projects such as digging of new retention ponds and stripping of ditches that had silted over. The work didn't stop there,says Maloney.

"Toward the latter part of the lake excavation, while it was being evaluated by engineers, we did an emergency dig to help out a utility crew on a nearby street. Time was of the essence and, again, we really benefited from having the Topcon GPS system in place. It told us precisely when we were at the required depth to allow the utility crew to get in and do their work. Any time you can pick up an additional project or two and keep people and equipment working, it's a plus for everyone."

Maloney says they had initially planned on wrapping up their portion of the development in the spring but, because of the pace they kept, the majority of the work has now been completed.

"While we are very pleased with the time savings alone, I feel it's important to note that the Topcon GPS not only speeds up the process, it improves the quality and efficiency of the work we do. It gives the engineers exactly what they want every time. We had an area on-site leading from the lakebed up to the home sites that was extremely challenging. It was a step-like feature that went from the lake, up to a flat safety berm, up to a trail, then to another flat spot, then up to the back of the lots, then up to another flat spot, and finally up to the top of the walkout where the houses actually sit."

Despite it being a very complex situation, he says the 3DXi allowed the operator to make the cuts needed for each level without setting any stakes at all. With those cuts in place, JAM's dozers and scrapers followed with all the flatwork.

"There were so may times throughout the course of the job that the GPS helped us out, but this was a facet of the project which really proved that our decision to add the Topcon system was the right one. It's been a nice addition to our business."