French contractor meets tolerance after machines pass over a one-centimeter (.39 inch) capping layer, saving material and avoiding rework

APRR, a subsidiary of the well-established  Eiffage Group, was selected for construction and project operation of the A719 road expansion, estimated at approximately €100 million ($111 million US dollars). This effort included building a 14 kilometer (8.7 mile) motorway link between the cities of Gannat and Vichy in Central France. The project consisted of widening the existing road to four lanes over one kilometer (.6 miles) following the current A719 route. This roadwork project essentially gives motorists an alternative to taking the small RD2209. 

Starting in the fall of 2012, archeological assessments around the site and initial utility work were completed, and forested areas surrounding the site were prepared. 

Integrated with the Eiffage Group, Forezienne d'Entreprises was hired for the development and civil engineering phases of the 135 hectacre project. Forezienne d’Entreprises began the development phase of the project in the spring of 2013. The company was responsible for excavation, sanitation works, implementation of the roadway subgrades, and utilities. Looking for improved productivity during excavation and precise grade accuracy, Forezienne d'Entreprises turned to Trimble and SITECH France for assistance. 

Solution: 

The team adopted Trimble® Business Center – HCE, Trimble GCS900 Grade Control System on six different machines while the construction survey team used Trimble Site Positioning Systems with the SCS900 software. Three bull dozers and one grader were installed with Trimble GCS900 Dual GPS and two graders with the Trimble GCS900 Grade Control System with SPS930 Universal Total Station for the finishing work.

Benefits: 

• Completed roadwork and installed 16 separate civil engineering works, 10 water retention ponds and one toll plaza all in two year timeline
• Excavated 1.5 million cubic meters (4.9 million cubic feet) of earth 
• During the subformation phase 8,500 cubic meters (27,887 cubic feet) of capping layer of aggregate was applied every day at two stations. This process took 11 to 12 hours of work per day; very little time and material was wasted, saving significant costs in rework
• During inspections nearly 100% of the points were within tolerance after the machines passed over a one-centimeter (.39 inch) capping layer screed

The scope of work covered 135 hectares and required the installation of 16 separate civil engineering works, 10 water retention ponds and one toll plaza. Serge Lafaye, Chief Surveyor for the A719 project, explains that a total of about 150 people were mobilized in the various phases of this job. Lafaye supervised a team of surveyors, a team for excavation and another team in charge of plant operations. Eighty to 90 pieces of heavy highway equipment were also utilized. 

"Trimble equipment is ideal for construction job-site working conditions: robust and intuitive, its ease of familiarization and use won over all the users, even those who were accustomed to working with competing equipment," said Lafaye.

Construction survey in action

The team used Trimble Site Positioning Systems with the SCS900 software for earthworks and construction survey in the initial stages of development and throughout the project. 

“The SCS900 software is intuitive and designed for the construction site,” Sylvain Sauvignet, Forezienne d'Entreprises surveyor on the earthwork team. “Everything is done from the same screen and it is all quickly accessible. It only took me a week to become familiar with it."

Used with the Universal Total Station, SCS900 allowed site engineers to easily check grade, stake and measure as-builts efficiently and accurately, without slowing down operations. 

“We opted for Trimble equipment because it is especially well suited to large construction projects such as BPL or the A719,” said Olivier Richard, head of the surveying department at Forezienne d'Entreprises. “It is precise and of very high quality. This investment was also driven by the quality of SITECH's service: their service-after-sales is very responsive."

The second phase of the project was devoted to major works such as excavation/backfill, installation of sanitation works, underground waterworks, and the installation of a fiber optic network that runs beneath the motorway's emergency lane. 

"The decision to equip our heavy equipment with Trimble grade control systems reflected a will to maximize the use of the equipment in order to save time in scheduling and achieve savings," said Pascal Perrin, Forezienne d'Entreprises lead job site superintendent.

In total, during the excavation phase, 1.5 million cubic meters (4.9 million cubic feet) of earth were moved. Perrin explains that the team also improved safety on the jobsite because he was able to keep his surveyors off the ground. 

"We improved job-site safety while also working with greater efficiency than before, and now we have a rendering in the vicinity of one centimeter with GPS and a half centimeter when the machines are guided by the Trimble SPS930 Universal Total Station," he said.

The third phase of the A719 project is the application of the road material, roadway furnishings and drainage. In order to widen the existing road to four lanes, the team had to grade to the subgrade level; then place the aggregate mix for asphalt paving.  Lafaye explains that when widening a road, accounting for proper water drainage is also critical. This includes placing gutters and earth and concrete culverts to collect water to be transported to treatment centers. He explains that it’s imperative to lay material to the appropriate depth because if it is not, water may become trapped at the base of the original pavement and cause weakness in the expanded roadway.

For grade work, the Trimble SPS930 Universal Total Station provides the exact position, accurate cross slope and heading of the blade. Lafaye explains that this was particularly advantageous for complex design surfaces such as super-elevation grading tasks faced throughout the A719 build. During the subgrade level phase 8,500 cubic meters (27,887 cubic feet) of capping layer of aggregate were applied every day at two stations; this process took 11 to 12 hours of work per day.  

Grading precision with Trimble

Lafaye insists that the guidance systems play a key role in the grading of the capping layer treated with hydraulic binder. 

"Once the material is delivered, it needs to be completely graded within three hours,” said Lafaye. “After that time period, the material hardens and becomes nearly impossible to grade correctly. Automatically guided machines allow us to grade the capping layer quickly and thus avoid needless touch-ups, which are ultimately a waste of time, materials, energy, and money.”

The operator of a grader equipped with a Universal Total Station-based GCS900 system also believes the improved accuracy helped to save significant rework across the project. During inspections nearly 100% of the points are within tolerance after the machines pass over a one-centimeter (.39 inch) capping layer screed. 

"As for implementation of the capping layer, it takes about three passes by the machines: a first pass to spread, a second pass as a "rough" grading with a bull dozer, and lastly a fine-grading pass by the grader,” said Lafaye. "Previously, the surveyor was called upon to come and check the grading. Now, the equipment operators can be free of continuous topographic tracking. The time savings are enormous. Since there are fewer passes, it's better for the blade. We work both faster and more accurately.”

Changes in construction surveyors' work flow

In addition to optimized machine use, Lafaye also used Trimble Business Center - HCE software for data preparation, 3D modeling and to seamlessly share information from the office to the field. 

"The design is created in the office and is sent to the machine's control box,” said Lafaye.  “The surveyors spend less time on the setting out and focus more on job site monitoring."

Lafaye attributes the success of the A719 roadway build to better data workflow, site positioning and tremendous grading accuracy delivered by on and off machine Trimble technology and support from SITECH France. He believes without Trimble’s construction technology these results could not be achieved.