E.On – Exeter

Project Details

Client / E.On

Exeter Western Transmission Main project

3D Technical Design (3DTD) were engaged by E.ON to develop the detailed design and complement the delivery of the Exeter Heat Network’s extensions in Cranbrook and Monkerton. The design scope comprised the extension of the Western Transmission Main, Eastern Transmission Main, Northern Transmission Main and various other distribution mains.


This work ticks all the boxes of service, turnaround, response time, flexibility, competence, quality...

CaseStudy-ExterThe design work and pipework installations took place on Tithebarn Way and across the M5 motorway, Langerton Lane, Pinn Hill, Hollow Lane, London Road, and exceeded a total of 5km in length.

By introducing 3DTD’s approach of GPR and topographic survey, 3D utility modelling, 3D network design and advanced HAZID processes, and through early coordination with Highways and Structures, the project risks were identified in advance and control measures recommended to de-risk the project pre-construction. Furthermore, by identifying accurate excavation depths, civil and pipe installation costs were reduced, which enabled the landmark project to proceed.

CaseStudy-ExterDue to the requirement for the installation of a large medium-pressure gas main, along the Western Transmission Main on Tithebarn Way, the design had to take into account, the need for wider trench excavations and reduced access for vehicles. To keep the road open and limit the disruption of traffic, numerous options were evaluated, including integrated trenches where practicable, separate trenches where the highway could not be kept open with a wider single trench, and sections where the road could be closed for a limited time. Thanks to the detailed pre-construction design and trench excavation sequence planning, the installation was a great success as testified by E.ON:

This work ticks all the boxes of service, turnaround, response time, flexibility, competence, quality. Everything I want from an external company. You guys truly are the best in class at what you do!


CaseStudy-ExterOne of the most challenging elements of the project was the crossing of the M5 motorway. The district heating pipes were installed through a 65m long concrete jacking pipe, thrust bored under the motorway, with approximately 8.5m depth at its deepest point.

3DTD carried out stress analysis and detailed pipe design and advised E.ON on the optimum approach to compensate for thermal expansion and maintain the integrity of the pre-insulated steel pipes, while making provision for future maintenance by adequate selection and positioning of the pipe supports.

Liaison with clients and subcontractors, as well as reviewing, organising and governing design supplied by third-party engineers, have greatly contributed to the success of the project.


The project team overcame significant technical and coordination challenges during the design and installation of the DN250/450 DH pipework through the tunnel, thanks to close collaboration between all stakeholders.


Stakeholders included:

  • Client (E.ON)
  • Therma-Mech Ltd
  • CPC Civils
  • Joseph Gallagher Limited
  • Technics Utility Surveyors
  • Devon County Council
  • Highways
  • Structures