Around the country construction sites are changing. The days of pegging out key points of a building or a road are numbered and pins are being phased out with machines rising up to take up the challenge.
So-called “machine control” is now creeping onto site and if you do not know about the technology – you should.
The use of machine control is no better demonstrated than on the £380M A1 widening project between Leeming and Barton, south of Darlington. This last remaining 20km long section of dual carriageway on the main road connecting Scotland to the south of England is being transformed into a three lane motorway in a long awaited upgrade.
Here, specialist global positioning system (GPS) 3D technology has been embraced across the whole of the project by joint venture (JV) contractors Carillion and Morgan Sindall after an extremely successful trial on the previous phase of the project.
The A1 widening project
The £380M scheme which includes £268M of construction cost commenced in March 2014 and completion is planned for spring 2017. It comprises three sections: the southern, central and northern sections.
Both the southern and northern sections are being widened either with one new lane on either side of the existing road or by building two new lanes to one side and moving the central reservation to give three lanes on the non-widened side. In the central section, the road is being realigned and the existing road detrunked.
Currently the northern section is 59% complete, the central section is 66% complete and the south section is 79% complete.
The works are complex with construction affecting 61 structures, including building 13 new and demolishing 13. Just to add to this there is 125km of drainage, 3M.m3 earthworks and 625,000t of pavement (road surfacing).
Client: Highways England
Contractor: Carillion-Morgan Sindall joint venture (JV)
JV designer: Aecom/Grontmij (Sweco)
“It’s a culture on this project to embrace technology,” says the JV’s planning manager Tom Stanton.
The system works by installing sensors on the plant equipment, for example, on a bucket of an excavator. These sensors send accurate data about the plant’s location and combine it with the 3D building information model and survey models. This is then used by the plant’s operator to work more accurately and more efficiently. Up to date 3D models can be sent directly to the screen in the cab without a piece of paper in sight.
All of the plant on the A1 project is fitted with such sensors and GPS technology. Here, dozers and excavators, fitted with Trimble machine control, have been used to move around 3M.m3 of muck. Cuttings up to 9m deep have been created to high surface tollerances while other areas are being filled with the excess material. The sensors on the plant have also been used to lay all of the layers of the pavement from the sub base, through to the blacktop which comprises a base, binder and final surface course. Graders fitted with GPS were used to trim the surface courses giving a high level of accuracy on the horizontal and vertical axes.
Such is the demand for the new technology, that new plant leaving factories of the principle industry players is now fitted with brackets as standard to allow the system of choice to be easily attached. Older plant can also be retrofitted with the necessary equipment to carry the new technology.
It’s a culture on this project to embrace technology
When it comes to the operators who use the plant on a daily basis, the new technology has been embraced, even by those who might traditionally be thought to prefer conventional techniques.
“In terms of the operators on site, there’s a good mix of old and new,” says Sitech heavy civils sales consultant Peter Brooks. Sitech supplies the Trimble equipment to the project. “Even the old hands, after a matter of hours, know what they’re doing and by the end of the week they don’t want anything else.”
Carillion Morgan Sindall JV survey manager Keith Kemp-Dillon adds that the operators can now take more control of their work and therefore have the systems in place to ensure all files containing design information are the most up to date versions. This makes the process more efficient.
“The operators aren’t relying on someone to come and set it out for them, as long as they have the correct files then they’ve got everything they need to continue,” he says.
“We have a system in place to make sure that they’re using the most up to date files.”
We’re confident that we’re achieving sub-millimetre accuracy between the stations
Files are transmitted to the plant on site via radio signal and, in addition, to the main base stations, special repeater units have been installed at key locations to ensure that there is good coverage across the site.
“You do get radio interference, but we’ve put additional repeater units in and the two base stations at Leeming and at Scotch Corner have got their own unique [telecoms regulator] Ofcom-approved licenses so they get less interference,” says Kemp-Dillon.
The system works to improve the accuracy of the work while it is being carried out, and also improves checking accuracy.
Kemp-Dillon says that to check an area, the machine control GPS antenna can simply be removed and replaced with a prism. This can then be used in conjunction with a total station via a radio link to give a greater degree of accuracy of work completed.
“We have a network of control stations throughout the project and they’re all digitally levelled so we’re confident that we’re achieving sub millimetre accuracy between the stations,” says Kemp-Dillon.
Brooks also points out that the frequency with which the works are checked is also increased. This allows the model to be updated and changes which are required to be implemented faster and more smoothly.
“You’re now controlling that model every centimetre of its distance rather than two guys pulling a string line of 10m chainage – what’s in between those 10m is anybody’s guess,” explains Brooks. “Now it’s checking it 20 times a second and comparing it to the models and making fine changes.”
But there is still a way to go to maximise the efficiency of the system, says Carillion Morgan Sindall JV construction manager Ashley White. He points out that as the pace of change has overtaken the standards, designs are still not where they should be.
To fully use the potential of this technology, standards need revising. Only then will you get full efficiency out of the machines
“The standards haven’t kept pace with technology,” says White. “We’re now trying to shoehorn new technology into old standards.
“To fully use the potential of this technology, those standards need revising. Only then will you get full efficiency out of the machines.”
This, he says, will come with clients like Highways England specifying machine control on its jobs.
Despite this however, the benefits of using the system could not be clearer to the team on site. Kemp-Dillon says that the vertical tolerances on the build up of the different layers is able to be far tighter than the allowable range leading to a far more precise job.
“We’re permitted to have a [vertical] tolerance on the sub base of +10mm to -30mm,” says Kemp-Dillon. “On this project we’ve actually targeted 0mm to +10mm on the sub base and generally we’ve achieved this tolerance without very much effort.”
Brooks says that because of this accuracy in the different layers, it leads to a consistent finish with the ridability as good as is possible.
Stanton agrees, “When you drive up and down there, you can tell it’s been done with machine control.
“It really is a beautiful bit of road.”
Technology used on site
The use of technology on the project has been one of its main focus points and the Carillion/Morgan Sindall JV has managed to pack a lot in.
- Automatic number plate recognition technology. Used predominantly by the police, it enables the contractor to allow only recognised vehicles to enter site.
- Electric car charging points. The project has four in use all day, every day.
- Finger print recognition. It might sound a little bit 007, but the team has also installed a finger print recognition system for authorised personnel to get access to the site offices.
- Tablet devices. In the reception area these give an overview of the project and relevant safety information and allow visitors to browse who is who on site. All personnel are listed with a photo and short synopsis of their role on the project. A Facebook for site if you will.
- Electronic snaggig document. Snags and problems on site are geographically linked and tagged in an electronic snagging document, allowing the history of an area to be brought up at the touch of a button.
- ”Personal shields” Plant is equipped with a new “personal shield” system. If a worker strays into the path of a machine, it is instantly disabled and a warning is sent to the driver.
- 360°video Six GoPro video cameras secured to a pole record a 360° view of the site, which can then be used to train site operators and for logistics planning.
Use of technology extends to live traffic using the A1 during the widening work. In some areas, the second lane is narrowed with heavy goods vehicles banned to allow the extension works to be carried out.
A number of accidents had occurred in the area and it was found that heavy goods vehicles (HGVs) driving in the second lane, were one of the major causes. The team then worked with speed camera manufacturers to slightly change the angle of the laser to recognise HGVs straying into the second lane. Cameras then record the number plate and can send the offending company a fine.
As part of a prevention campaign, letters were sent to all local HGV users explaining the measures. To date, the threat of being caught has meant that the team has not had to fine anyone yet. Through this simple measure, the accident rate on the Leeming to Barton section of the A1 has been vastly reduced.
“There’s been a 94% lane reduction in accidents,” says Carillion Morgan Sindall JV planning manager Tom Stanton. “So it’s now being spread across the country. The cost was almost nothing as it was just a small modification, but it’s saved lives and accidents. It’s also helped the flow of the traffic.”