During November, a significant amount of construction work has been undertaken in the areas of the new Westley Bridge, new slip roads and what will be the new A46 gyratory.
Overview:
During November, a significant amount of construction work has been undertaken in the areas of the new Westley Bridge, new slip roads and what will be the new A46 gyratory.
The most noticeable aspect for the public travelling through the works area is the opening of the new northbound on slip. Public traffic is now using the new slip road to head north and the old northbound on slip has been decommissioned in order to create a working area to assemble the deck of the new A46 Bridge.
The earthworks fill operation has continued throughout together with early-stage construction of the new Dalehouse Lane roundabout taking place. Work has also been undertaken in the form of drainage and kerbing although this will be an ongoing process over the next few months.
Progress to Date:
Westley Bridge Cofferdam
Throughout the course of the month, pile cropping has taken place on the northside of Finham Brook to prepare for constructing the pile caps and subsequent abutment foundations. Pile cropping is the process of reducing the height of the previously installed concrete piles to the correct level in a manner which ensures that no damage occurs to the pile reinforcement steel. A specialist piece of equipment – called a pile cropper – undertakes this work and reduces the concrete down and leaves the reinforcement steel protruding. An image of the completed cropped piles can be seen in Figure 1 and a pile cropper can be seen in Figure 2. Although the pile cropper carried out the majority of the removal, operatives completed the final stages to create a level platform in preparation for fixing the reinforcing bars to the pile caps. Integrity testing was carried out to check the piles had not been damaged during the cropping process.
In the future, reinforcement steel will be fixed around the protruding pile reinforcement and will enable the casting of the pile cap. This ensures that the pile cap works as a single structure in conjunction with each pile and the entire structure must consider things like freeze thaw weathering, ground conditions (including groundwater) and the potential for ground movement.
This is done by fixing a “cage” which is then ready for the concrete pour. Formwork will be placed around which will contain the wet concrete until it has time to set.
Northbound On Slip
At the start of November carriageway surfacing was completed for the northbound on slip. This led to the successful opening of the new slip road on the 8th November. A temporary running surface has been laid on the west gyratory and will be surfaced with the final material when the rest of the gyratory is constructed and also to allow construction works to continue around the area. The old slip road has now been decommissioned to create a temporary working platform to assemble the bridge deck for the new A46 bridge. Figures 3 and 4 show the new slip road and gyratory arrangement.
New A46 Temporary Working Area for Bridge Deck Assembly
With the opening of the new northbound on slip road to traffic, the original northbound on slip has been decommissioned. The area will now serve as a temporary working area to construct the new A46 bridge deck and in the future, the deck will be manoeuvred into its final position.
In order to do this, a large part of the original slip road has been flattened and a temporary working platform created. A series of four trestles have been constructed and adjusted to the correct level. These form a support for the future bridge deck and are an essential part of ensuring there is a working platform for the deck assembly. The deck will comprise of eight number beams in total. However, pairs of beams have been connected together forming four pairs of beams as a single unit. They are being manufactured in a specialist steel building facility and - during the weekend of the 27th November 2021 – three pairs of beams for the new A46 Bridge were delivered, with the last beam planned to arrive midway through December. Figures 5 and 6 show the three pairs of beams that have been delivered to site, along with a close up showing the interconnecting pairs of beams.
Attenuation Pond
Significant progress has been made in terms of constructing the second attenuation pond alongside the existing Stoneleigh Road. Attenuation ponds allow rainwater to be collected from the highway drainage system and reduce the risk of flooding in the area. Attenuation ponds are a proven environmentally sustainable system for dealing with rainwater from a road as they can remove urban pollutants from rainwater from a road through the planting of a variety of aquatic vegetation and water plants. The ecological benefits can be substantial due to the opportunities generated in terms of development of wildlife habitats.
Further Information:
The construction work to Westley Bridge will continue in the form of steel reinforcement caging on the north side of Finham Brook and the pouring of the concrete for the pile cap. On the north side, further excavation and the installation of sheet piles will enable the piling to be cropped in a manner similar to that reported previously for the north side. The earthworks fill process will progress with emphasis on the development of the new Dalehouse Lane Roundabout.