Norse Highways, a partnership with Norfolk County Council, is part of Norse Group, the UK's leading local authority trading company. This is the story of how Norse Highways combined its in-house expertise and collaboration with partners to handle an emergency in Norwich.
In March 2022, a significant carriageway collapse occurred at Whistlefish Court in Norwich. The carriageway lies in a densely populated area two miles from the city centre; it is an adopted highway with a single route in and out serving approximately 100 properties. The key priority for this project was to repair the damage quickly and with minimum disruption to the residents.
It was believed that underground water had washed away fines from the ground causing the road to collapse and, in turn, caused a significant leak from the water main. This had a notable impact on the main utility supplies within the area.
Due to the collapse (pictured above), lost water from the main line and soil fell beneath the surface of the carriageway. As a result, this material is likely to have entered a natural dissolution feature or a man-made void.
The size of the collapse, location, and nature triggered a significant out-of-hours response. Norse Highways acted quickly making the area safe, initiating emergency work with the affected utility companies, putting temporary access in place for road users, and supplying traffic management.
Whistlefish Court was initially constructed above infilled pits. Lime kilns shown on historical mapping indicate that chalk was taken from the pit. However, in 1990 after a case of subsidence, tunnels were found within the chalk beneath a neighbouring crescent. It was found that similar tunnels extended to the east of the pit directly beneath Whistlefish Court.
Initially, the site was investigated by Norfolk Partnership Laboratory (NPL) using a ground penetrating radar to determine the extent of the shallow voiding around the collapse, other uncommon features, and the location of various utilities. This was followed by dynamic probing and window sampling. The purpose of the probing was to locate any voids at depth and to assess the ground's load-bearing capacity for larger plant, which would be required to assist with repairs due to the project's complexity.
Norse Highways also commissioned a geophysical survey using microgravity techniques to locate and identify the size and nature of any voids at depth. This microgravity survey identified areas of low and high gravity across the site.
Due to considerable interference from utilities, the surrounding buildings and the surface void, it was impossible to determine whether a chalk tunnel was present or whether the lost material had entered a natural dissolution feature.
NPL carried out further dynamic probing and window sampling to examine further the features identified by the microgravity survey. This proved that the low gravity features were voids beneath the carriageway or sewer access chambers. The high-gravity areas were shown to be dense natural sand that had not been disturbed by quarrying. The neutral areas were comprised of well-compacted fill to the old pit.
On determining the extent of the voiding as accurately as possible, the base of the hole was cleared of loose debris and then plugged with foamed concrete. Norfolk County Council’s Structures team then designed a reinforced concrete slab; this was constructed above the foamed concrete and extended to ensure that the ends were founded on good natural ground.
In addition, the design provided that constructed sections could support and facilitate all works and equipment as the repair work was completed in stages. The highway was then reconstructed above the slab using conventional methods.
This project required a highly collaborative approach with utility companies, emergency services and refuse collection providers, ensuring that everyday life continued for the residents.
Support for this project was provided from within Norse Group, including site security, marshalling of residents and structural surveys of neighbouring properties. In addition, the Norse Highways Compliance team, along with the Norse Safety Health Environmental and Quality team (SHEQ), were heavily involved in the operation, bringing significant experience and expertise. This ensured that the highest safety standards were maintained, protecting residents, staff, contractors, and the public.
(Good as new: The road after the repairs.)
Norse Highways (part of Norse Group) provided significant engineering support to the Highway Authority and Norfolk County Council by deploying its specialist lab (Norfolk Partnership Laboratory), highways operations, civil engineering, and groundworks teams. The use of in-house resources ensured a joined-up approach and allowed for a rapid response and quick completion – as well as ensuring value for money.
The Group's well-established supply chain contributed significantly to the operation's success. In addition, specialist providers of ground support equipment and plant played their part as Norse achieved the balance between employing appropriate long-reach equipment and working within the known capabilities of the surrounding ground and the wider environment.
The nature and scale of the collapse at this location were severe and had a significant impact on residents, which would have been far worse if Norse Highways had not acted so quickly and effectively. In addition to the immediate highway requirement, essential underground services were affected, which required coordination with utility services to repair or divert and restore supplies to the community.
Norse Highways was the lead in delivering the works to reconstruct the highway. Furthermore, Norse Highways used their labs' extensive experience to undertake the ground investigation, calling on specialist contractors for a detailed microgravity survey. In addition, the expertise within Norse was invaluable in maintaining site safety and security in a challenging location.
Karl Rands, assistant director of highways services, Norfolk County Council, said: 'The contribution of Norse Highways was significant, professional, and produced a durable and quality outcome for Norfolk.'
