Swindon Borough Council and contractor Osborne Infrastructure Ltd are taking decisive action on major works at the White Hart roundabout after groundwater levels were found to be much higher than expected.
For the last three weeks, Osborne has been building the road’s sub base from scratch after serious defects were uncovered earlier this year. Engineers then found that the higher than expected groundwater table had severely weakened the underlying clay, which props up the road base.
Osborne has dug down almost a metre beneath the surface to build a new structure for the road base of the roundabout and is adding reinforced plastic grids due to the discovery of the groundwater levels.
In order to strengthen the road surface and subsequent layers so it can take the weight of heavy goods vehicles for the next few decades, 'a modified road structure design is being introduced which will involve laying reinforced plastic grids above the clay and between the stone layers,' Swindon BC said.
The grids distribute the vehicle load across a wider area, extending the working life of the finished road.
Cllr Gary Sumner, deputy leader of Swindon Borough Council and cabinet member for strategic infrastructure, transport and planning, said: 'It is only when you get right underneath the surface that you begin to get the full picture of what is going on and the work at White Hart is proving to be a case in point.
'Although the extent of the problem with the groundwater softening the clay undersoil was unexpected, we have been quick to identify a solution to redesign the scheme and this means we can rebuild the junction and be confident it will be fit to last for decades to come.
'We anticipate the extra work could take four weeks but our contractor is working six days a week, 12 hours a day, so will be doing everything possible to claw back that time.'
As a result of the extra work the roundabout closure could be extended for an additional four weeks. The extra work is being paid for out of contingency funding for the overall scheme, Swindon said.
Access continues to be maintained for emergency services only and diversions remain in place for all other road users.
Road traffic is still open to use the junction to leave the A419 southbound to join the A420 eastbound, or to leave the A420 westbound to join the A419 southbound only. This has allowed the contractor to maintain access to St Margaret’s Retail Park, Sainsbury’s, the Truck Stop, and other businesses on the A420.
White Hart roundabout is one of several key junctions being upgraded to help mitigate the impact of the New Eastern Villages (NEV) development being built to the east of the A419.
The overall £30m improvement scheme is due to be completed in February next year and also involves creating a new bridge over the Great Western Mainline and a new northbound slip road. Although traffic is due to use the roundabout later this year.
Once completed, improvements to the junction will include an increase in the number of lanes on the roundabout, the addition of traffic signals and the widening of the A419 southbound slip road.
Residents can stay up to date with roadworks as part of the New Eastern Villages (NEV) scheme by signing up to the NEV newsletter: www.swindon.gov.uk/newsletter