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SAFETY BARRIER & FENCING PROJECT

A421 Noise Barrier Replacement

a collaborative approach with the client, designer and specialist supply-chain

Carnell installed a mile of noise barrier across three sites on the A421 in Bedfordshire for National Highways in the East region.

Scheme Background

Since being installed 15 years ago when the A421 was upgraded to a dual carriageway, the noise barrier adjacent to the A421 had fallen into disrepair. Despite repeated interventions by National Highways’ Maintenance & Response contractor, rotting timber posts and collapsing panels led to several sections having to be removed, significantly reducing its effectiveness.

Carnell were selected as Principal Contractor by National Highways, responsible for managing the removal and replacement of the barrier with a more durable and effective solution. This would mitigate environmental issues in these Noise Important Areas.

Delivered through the Construction Works Framework and latterly the Scheme Delivery Framework, National Highways also employed Atkins Realis as the Principal Designer and HW Martin as Traffic Management Provider.

ECI & Construction Phase

The initial proposal was for a like-for-like system, but there were concerns over the longevity and compliance to LD 119 standard. During ECI, the scheme evolved and the Principal Designer accepted the suggestion of auger boring to create 2m deep foundations, as well as the use of resilient and recycled Tilon Noisewall reflective panels.

SITE 3

We mobilised in November 2022, to start work at Site 3: Wootton Eastbound. However, it soon became apparent that difficult ground conditions were hampering the removal of the old barrier and installation of the new posts. Work was needed to improve the barrier design, and we sought the advice of our specialist barrier supplier Versco. Working collaboratively with Atkins Realis, a new methodology was agreed and we returned to site in March 2023. Versco supplied 10 hydraulic formers to create the shuttering for a reinforced concrete beam foundation and the steel in the piles was tied into this structure. With works progressing smoothly, an installation team followed behind, 3m high fence posts were bolted into anchor plates and the lightweight Noisewall panels were slid into place. The result was an acoustic fence measuring 350m in length.

SITE 2

Further work was done with the foundation design and we returned a few months later to replace the noise barrier at Site 2: Lower Shelton Eastbound. The reinforced concrete beam foundation was specified, with auger piles no longer required. The old barrier and foundations were removed and excavation carried out to the required levels. A challenge to the specification meant that once the foundations and posts were in place, Versco ‘VC+EB-L2 system’ absorptive panels and capping were lifted into place. This formed a 414m long barrier which was 3.2m high.

SITE 1

Upon receiving the task order for Site 1: Marston Moretaine Westbound, we commenced the construction phase in February 2024. The work here was split into three phases due to the differing ground conditions. Phase 1 again used the reinforced concrete beam foundation. Phase 3 was the second to be undertaken and had the added issue of a narrower working area congested with utilities, due to the adjacent Bedford Road which was also about a metre lower. The existing barrier had been mounted on a gabion wall which needed to be replaced with a more suitable foundation. We used sheet-piles and a concrete pour to create a level base which brought it up towards the level of the A421 along a 200m stretch. Pre-cast concrete beams were laid on top to form the foundation for the barrier. Finally Phase 3 was completed in the same way as Phase 1. This created a continuous 807m long barrier of absorptive panels.

Sites & Phasings

This section of the A421 is between Milton Keynes and Bedford. 

The order of the sites and phases was as follows:

Site 3: Wootton 

  • Eastbound from MP 9/9 to 10/2

 Site 2: Lower Shelton 

  • Eastbound from MP 6/7 to 7/1

Site 1: Marston Moretaine

Westbound

  • Phase 1: MP 7/0 to 6/5
  • Phase 3: MP 7/2 to 7/0
  • Phase 2: MP 7/4 to 7/2
locations of noise barriers installed

Overcoming Barriers

In total, a 1571m length of noise barrier was replaced. 525 posts were erected with a similar number of panels which had an area of more than 5,000m2 – the same size as a football pitch!

There were many challenges to the programme, but we were praised by the client for our proactive and problem-solving approach. This led to National Highways requesting that the same team deliver their A1 St Neots Noise Barrier scheme.

Benefits

Safety
  • Zero RIDDOR Reportable Incidents across 37,000 working hours.
  • 208 Near Misses reported.
  • Pre-cast base blocks had integrated fall-arrest system.
Customer
  • The new noise barrier protected residents from the noise of 55,000 vehicles per day, a traffic count which has doubled in the last 20 years.
  • Mobile VMS deployed for road user information / updates.
  • Roadspace shared with M&R and road marking scheme.
  • Working from the Bedford Road under signals to reduce TM on the adjacent A421.
Delivery
  • Collaborative approach between client, designer and delivery partners from ECI to completion.
  • Change management approach to overcome challenges to keep delivery on track.
  • Efficiencies created from the manufacture of 10 innovative hydraulic formers.