SPECIAL WORKS
The suction excavator to one side of the bridge culvert site which also allowed pedestrian access to be maintained throughout the works.
structures. The sub-contract for the surface removal and Vacuum Excavation was appointed to Vac UK Ltd, a Kilkern Company.
On site Vac UK Ltd operated its RSP- manufactured, twin fan suction excavator which is based on a Mercedes tridem AROCS 8x4 chassis. The twin fan system creates a suction power of 44,000 m3/h and a max vacuum pressure of 55,000 Pa.
The opening works were completed in relatively small sections, about 500mmwide, with the outer culvert wall being exposed using the small hydraulic pickpowered from the vacuum excavator and the spoils being removed as the road surface was broken down. This was possible because the weight of the vacuum unit did not have to be placed on the bridge structure directly but just to one end. This meant little or no direct excess loading on the bridge/culvert structure. Once the road surface was removed and the depth of the excavation around the crown and down the arch sides progressed, spoil removal became easier as the soil type changed from hard road and substrate to softer soil type materials. Once a section of arch was exposed over about 2 to 3 m, the section was cleaned and grouted to provide the extra support needed. This process was repeated until one side of the bridge was completely supported. Excavation then moved to the other side of the road and the process repeated.
Once the full width of the culvert arch was fully grouted the road surface was backfilled and
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Once the surface works were completed the inside of the culvert was hand-grouted and repointed.
replaced to the required standards, the operation switched to the inside of the culvert.
Removing all but the necessary internal support, a man-entry system was established within confined space working regulations. The inner surface of the culvert was then cleaned and repointed using the specially formulated lime mortar to provide a finish that closely resembled the lookand form of the culvert as it would have been originally constructed. All supports were then removed and the culvert and bridge returned to normal operations.
With the repair works completed the bridge will be able to carry all normal highway traffic loads up to 44 tonnes.
Commenting on the project for Somerset Highways Nick Jacklin, Senior Engineer – Structures said: “This was never going to be the easiest of bridge/culvert renovations given the Listed status of the structure. However, working together and utilising some of the newest vacuum excavation technology the project has been fully successful and we expect the bridge and its culvert to now be operation for many decades to come. Our congratulations must go to the Walters crew and the Vac UK team for enabling this to be the case.”
For Vac UK Ltd, Joanne Ashford commented: | August 2021 |
www.draintraderltd.com
“We were particularly pleased to be able to offer a solution for the uncovering of this culvert given its age and structural state. To be able to use such a large machine on such a delicate works programme has really shown us that vacuum excavation can be utilised in a variety of circumstances where many may not expect to find it operating.”
For Walters Group site manager, Craig Ellis said: “I must congratulate our team on the success of this particularly delicate operation. The utilisation of the vacuum excavation system really aided the success in exposing the fragile outer surface of the culvert whilst minimising any potential for further deterioration inside the culvert. This operation just goes to show how authorities, contractors and subcontractors can workclosely together to achieve a very successful solution to the most challenging of projects. I would also like to thankthe local population for putting up with us for the weeks necessary for the works. They have been patient and understanding even though they have been required to travel some extra distance to allow these works to be concluded successfully. I am sure they will feel the benefits now the road is fully open to all traffic.”
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