Flimby: State of the Nation – Culvert Rehabilitation

Location: Flimby, Cumbria

Client: Environment Agency
Contractor: Volker Brookes Atkins (VBA)

The Project

Further to previous successful works for VBA, NRC WWS LTD were invited to provide a fee proposal and methodology for Culvert Rehabilitation of 650lm of delipidated culvert (900mm diameter) running through the high street of Flimby.

The culverts had been subject to immense flooding issues in the past. Such was its chronic condition; some floods made the national news.

Our Proposal and methodology included innovative ideas of remediation. Consideration for the residents of Flimby was paramount as the proposed scheme was in the heart of the village community.


Scope of Work

Upon Award of the contract NRC WWS LTD presented the client with a Method Statement and Risk Assessment for each aspect of the works including but not limited to; Confined Space Entry, Over-pumping, Excavation, UV Lining works and Precision Cutting. During the approval process we visited site on several occasions to scope the works with the client and speak with local landowners to explore the possibility of renting land space.

An agreement was made with a local famer to rent space on his land for the duration of the contract period to set up a site compound and welfare facilities.

Following approval of our RAMS from the main client, we commenced with our mobilisation to site. The mobilisation involved delivery of site cabins / welfare facilities, plant and materials. This initial set up was undertaken by our Contracts Manager and site operatives prior to undertaking the main contract works two weeks later. Upon completion of the initial site set up an additional team of 12 personnel were mobilised to site to commence the works.

The scope of works was to undertake no dig culvert rehabilitation using non-intrusive repair methods which was agreed by the client to be a proven method of the Ultra Violet (UV) lining system of 18 different lengths of a 900mm culvert.


Installation of a 900mm UV Liner

To undertake the rehabilitation works, we firstly had to set-up an over-pumping system to take the stream entering the culverts away from our works area.

This involved building a cofferdam at the inlet and diverting all flows away from the works.
The over-pumping set-up was challenging in the fact that the diversion of the water was over 1500lm in length and involved road crossings and fields. This took away all the disruption from the village and its residents

A detailed Traffic Management plan was also submitted and approved by the local highways department to enable the works to be undertaken. The TM plan had to consider the local traffic flows and residents due to the location of the works.

Due to the existing condition of the culverts, with most lengths having no inverts and voids on the bottom of the pipe of more than 300mm deep, we firstly had to come up with the innovative idea of how to fill these voids without man entry prior to installing the UV liners.

After discussions with our technical department and various suppliers we decided that we would have manufactured a 900mm sponge pig.

This would enable our on-site personnel to pour a large amount of dry mix concrete into the manhole chamber and then winch the sponge pig through the culvert from manhole to manhole. This in turn would fill the voids, thus eliminating any risk to on-site personnel with the need for un-necessary confined space entry to fill the voids by hand.

Once the concrete had cured 24 hrs later, NRC then proceeded to winch into place the UV lining material for the final part of the rehabilitation.

Once the UV Liner had cured and all the lateral connections were reopened, we completed a post survey of the culverts proving they were back to being efficient and fit for purpose reducing the risk of storm water floods to the residents of Flimby.

The job was a total success and we were complimented by our clients.


Technical Challenge

During the project there was no contamination noted throughout any of the various watercourse and culverts. All plant and machinery used bio-degradable oils so in the event of mechanical failure there would be no detrimental impact to the environment.

The appropriate use of the correct PPE and RPE meant that the risks associated with this could be reduced to the lowest risk reasonably possible.

The infill of the voids within the culverts using the pig and winch system proved very Technical and Effective, which also eliminated the risks associated with confined space entry works and danger to our operative entering the system.

Key Facts

  • Work completed ahead of time and within budget
  • No injuries or incidents throughout the duration of the project
  • Project duration 15 weeks
  • 650lm of 900mm culverts located within the main street of Flimby fully rehabilitated using UV Lining techniques
  • New and innovative solution was used with the Foam Pig and the Voids in the culvert
  • Successful remediation of culverts significantly reducing the risks of floods for Flimby residents
  • All modular surfaces reinstated and signed off by local Highways inspector
  • No Pollution to existing watercourses during the contract period
  • All wastes derived from the project disposed of at licensed waste disposal facilities