Project in focus

Project Category:Infrastructure – Utilities
Project Name:Thanet Adit Exfiltration Project
Client:Clancy Docwra on behalf of Southern Water
Location:Thanet, Kent

Concrete Pipe After Rehabilitation

Thanet 4
Project Brief:Prevent exfiltration from the sewer network into the chalk ground in Thanet. A historic problem of surcharged sewers overflowing into the open chalk Adits (Tunnels) needed to be addressed. Clancy Docwra on behalf of Southern Water, engaged the McAllister Group to work with them to provide a trenchless solution to allow for the isolation of the sewer network from the ground regardless of flow volumes.
Client Brief:Reduction in ground water nitrate levels; the avoidance of deep excavation in narrow streets with few diversion options; Short works duration on any one site thereby minimising disruption for individuals and streets and minimal lorry movements within Thanet in contrast to the ‘muck away and reinstatement works’ associated with excavations up to 12m deep.
Works preparation:CCTV Survey of 7km of sewer using mobile works/minimum Chapter 8 to minimise resident and traffic disruption; Design of no dig solution to form an overflow network within the chalk Adits; Custom design of UV cured CIPP liners for the free in air installation and to be able to withstand adit damage or collapse; Installation of 7km of UV lining in over 80 separate Adit lengths; Adit entrance sealing by brick work; Installation of Tideflex valves on all downstream Adit brick ends to allow ground water release.
Solution:UV Cured GRP Liners custom designed and supplied by Impreg, with a custom developed outer grid foil to protect the liner from over inflation and impact loading within the Adits. The Impreg GL13 liner provided increased strength with a lower wall thickness than ever. 10% sampling of liners subjected to independent laboratory testing to confirm design strength achieved.
Outcomes:People – No public, staff or third party HSQE accidents or incidents during the project

People – No complaints from residents or road users at any stage, and no Fixed Penalty Notices issued. Clancy Docwra handled all the public interfaces allowing McAllister bros. to concentrate om the works on site

Technical – Liner strength: Long term Emodulus resitance = 14,900 N/mm2 and Long term bending resistance = 240N/mm2

Technical – All individual sites were typically mobilised, works completed and demobilised within 10 hours

Technical – Pipe depths range from 5m to 18m, making all sites subject to strict man entry controls

Environment – significantly reduced carbon footprint

Environment – all delivery packaging and timber recycled

Environment – Approximately 800 Kg of offcuts for entire project sent to landfill

Environment – 6 tonnes of silt and debris removed and treated as contaminated waste

Environment – No water was used in the cleaning operation with the use of recycling JetVac units utilising available flow

Client perspective:“The Clancy Docwra and McAllister solution avoided enormous disruption for our customers, and we have been delighted by the professional delivery of this work to date.” Norman Howell, Southern Water