DrainsAid, a division of Wakefield-based Peter Duffy Ltd, has successfully completed a major sewer rehabilitation project in Hereford for the Dŵr Cymru Welsh Water’s Capital Delivery Alliance. The Delivery Partner overseeing the project was Morgan Sindall working with Arup.

Higher than expected dry weather flows (DWF) indicated that groundwater was infiltrating a section of sewer and causing operational issues for the downstream sewage treatment works.

A CCTV survey confirmed the prognosis and it was decided the most cost effective and efficient option was reline almost 900m of the affected high capacity sewer network, with both hot cure and UV Lining systems.

The DrainsAid team surveyed the sewer and subsequent CCTV footage. The site investigations produced a refined rehabilitation design proposal, for both the large bore lining of the sewer and rehabilitation of a number of manhole chambers. The solution made full use of DrainAids’ experience and expertise in both CIPP (Cured in Place Pipe) and the innovative M-Coating technique’s utilised for the Manhole rehabilitation.

DrainsAid utilised cutting edge technology in the installation of large bore UV Lining system on this scheme, this method involves winching the protected Liner through the host pipe, inflating to the desired pressure and curing the light sensitive liner with a large UV light train that traverses the length of the liner at a controlled rate.

UV CIPP Lining

DrainsAid has invested heavily in market leading equipment, to complement its substantial fleet of specialist lining and rehabilitation plant, a Hachler HF200 cutter complete with an undercarriage was the preferred cutting unit used on this project to remove substantial encrustation and roots present in the sewer in preparation for the lining process.

For the large bore lining application, the site was protected using proprietary site barriers, upstream flows were controlled by over pumping water to the adjacent downstream manhole chambers, enabling a safe working environment for the teams and suitable application conditions for the liner and its associated equipment.

The scheme design called for some of the lining to be installed using the Hot Cure method.   To enable this lining process a scaffold tower was designed and erected above the inversion manhole, where lifting equipment fed the liner into the host manhole chamber. The end of the liner was clamped around an inversion ring , once secured the Liner was inverted using potable water from a fleet of 60,000 gallon capacity articulated Tankers , the liner was filled to capacity with the hydraulic force of the water pushing the liner to the desired position at the downstream manhole.

Heater hoses that were fed on site by a portable 3m BTU boiler were passed through the water filled liner, this process raised the temperature of the water through a time and temperature design schedule, until the cure rate was achieved and the liner was evacuated of the heated water and flushed with cool water to complete the curing process.

To complete the installation mechanical end seals were installed to stabilise the liner against the wall of the pipe ensuring a watertight seal and the lateral intersecting pipes were reopened using the robotic Hachler cutter.

A number of manhole chambers on this site were identified as in need of rehabilitation, to eliminate water ingress DrainsAid treated the vertical walls using the M-Coating System.

M-Coating is a proprietary manhole rehabilitation process developed by Hermes-Technologie, which greatly reduces the time on site in comparison with traditional techniques and provides a permanent solution to water ingress to the vertical walls of the chambers.

Prior to the M-Coating application, water ingress was identified and a specialist grout, Ergelit KBi was pumped into the structure of the chamber at the location of the leaks to fill any voids and stem all water ingress.

On this project, the manholes were jetted with high pressure water to remove debris grease and residues to create the optimal surface for the M-Coating application process. The product of choice for the given conditions was Ergelit KS1 a high performance specialist mortar ideally suited to this method of application.

The coating is applied using a centrifugal spray head attached to a vertical control arm. The arm is operated remotely from the control module at ground level and travels  up and down the manhole, achieving a 10mm thick coating in  as little as 30 minutes per chamber .

Hermes M-Coating Before & After

Hermes M-Coating Before & After

The many benefits of this operation are the minimal man entry into a confined space and the conservative application that is controlled by a computer programme ensuring appropriate coverage without waste.

By all key business metrics the project was a success. The completed scheme was fit for purpose and exceeded expectations.  The scheme was delivered safely and there were no reportable injuries or lost-time accidents.

The expansive site was in open parkland and had two adjacent schools, working with Morgan Sindall , a movement plan was established to protect all users of the Parkland.

The parkland houses a conservation area with native Otters and Wildfowl present, great care was taken to ensure the works did not adversely affect the Environment. The grassland was protected using a temporary roadway system to allow heavy plant to safely travel across the site without impacting the landscape.

Involvement with representatives from the schools and local groups at the planning stages and throughout the project ensured minimal disruption and an incident free site.

The solution we proposed was effective and allowed the team to showcase their skills and experience on a major sewer rehabilitation project in often challenging conditions.

Following the success of this project we are looking forward to further opportunities to work with water companies and other clients in the future.’

DrainsAid UV Lining


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