Texas construction firm documents 28% to 33% increase in productivity using Trimble Machine Control
Dust on a Houston jobsite is a given. The terrain is flat and the topsoil is hard. Combine that setting with long stretches of dry weather under an unforgiving sun and it becomes clear why Tony Clark, Survey Manager and Machine Control Technician, for M. Hanna Construction, refers to central Texas soil conditions as being “extremely challenging.”
Site-prep machines, working on the 82-acre residential subdivision on the far north side of Houston, are trailed by clouds of dust that can reduce visibility to near zero. “Soil conditions here at the Grant Meadows project are typical for the area,” Clark said. “The top foot is a hard, dense, but fertile topsoil. Below that is a three- to five-foot layer of what we call ‘black gumbo’ -- a low PI, sandy mix of clay and vegetative matter that during the wet season, or in undisturbed area, never really dries out.”
During wet periods, the ability to move equipment is extremely difficult, to say the least. Clark referred to instances when whole machines were nearly swallowed up by the water-soaked soil.
Considerable soil prep
Before work could begin in earnest on the Grant Meadows subdivision, M. Hanna spent close to 40 days performing soil prep to achieve the necessary soil densities.
“There is no natural aggregate in the area so we need to bring in very large mixers to add lime or fly ash to create engineered fill that can replace the top two feet of soil throughout the project,” Clark said. Once the soil is placed, it is compacted to the required density by using a vibratory sheepsfoot drum roller.
The 65 craftsman-quality, upper-middle price range homes to be built on this tract, will be placed on fairly large lots. The subdivision is flat. According to Clark, there is nothing over a one percent grade on any buildable surface or roadway throughout the entire project. “Conservatively, at least 80% of the project is designed at a half of a percent of slope. Because that’s nearly impossible to grade by naked eye, it becomes one of a number of reasons why we use GPS grade control,” Clark said.
When it rains, it pours
“When it rains in Houston, it’s like a deluge rather than a sprinkle,” Clark said. “So, as typical building practices in the area, each lot will be bordered by a drainage well that feeds into a retention pond.”
The storm water management plan has some complications that a GPS machine control system is well-suited to handle.
“We selected the Trimble® GCS900 Grade Control System to use on our two new Caterpillar D6N LGP Track-Type Tractors because it is powerful, easy to install and easy for machine operators to learn,” Clark said. “The capabilities of the GCS900 excel when dozers have to come up to a high point around the edge of the pond where the design plan calls for the placement of barely discernable catch basins. These formations are based on such a minute percent of grade that I can’t imagine accomplishing this without GPS grade control.”
Hard rains can also cause complications for M. Hanna in working on its sites. “The Trimble GPS system is instrumental in keeping a site clean and draining at all times,” Clark said. “We don’t have to worry about pockets of water forming after a downpour, which, in and of itself, keeps us productive and saves money by preventing redos due to mothernature.”
Time savings: GPS vs. no GPS
In talking about eliminating redos and saving time, Clark said: “Our primary reason for using the Trimble GPS system is that with one machine pass we’ve got an accurate grade…there’s no guessing. This ability becomes immensely valuable not only for flat grading but in complicated situations like we have here at Grant Meadows with its unusual drainage needs.
“We have proven through our experience and collecting data over the past five years that GPS grade control gives us a 28% to 33% increase in productivity. To do it any other way is truly archaic.”
Complex site plans welcome
For the future, M. Hanna Construction anticipates tackling more complex projects. “We literally have the most sophisticated GPS 3D grade control system available, said Clark. “It allows us to take on complex projects. For example, we recently completed the site prep for a new high school and its grounds. The project included building pads, ball fields, tennis courts, parking lot areas and an exorbitant amount of catch basins not only for open areas but along curb lines. We couldn’t have hit production deadlines and quality marks without the Trimble GCS900 3D Grade Control System.”
Published in Trimble Productivity, Fall 2005