M25 Junction 25 Improvement & Holmesdale Tunnel Refurbishment

The M25 London Orbital Motorway is a fundamental component in Britain’s motorway network designed to allow traffic to bypass London. Since its completion in 1986 it has become one of the busiest motorways in Europe. The northern section, where the Holmesdale Tunnel is situated, experiences traffic flows of over 120,000 vehicles per day.
Holmesdale Tunnel Refurbishment
Holmesdale Tunnel is a 650 meter long cut and cover tunnel consisting of two parallel bores aligned approximately east to west.

The purpose of the project was to upgrade the tunnel and junction from 2 lanes available for through traffic to 3 and refurbish the tunnel mechanical and electrical equipment which had reached the end of its design life and becoming beyond economic repair.

Work began on 6 May 2006 and was completed three months early in September 2007.

VVB were appointed by the main contractor, Costain to supply the labour and engineering services required to complete the electrical and mechanical installation elements of the project. Our involvement ranged from assisting with design, procurement and supplier selection to installation, testing and commissioning.

Our works included:

  • Installation of HV transformers
  • LV electrical switch gear and distribution network
  • Replacement of tunnel lighting system
  • Saccardo nozzle tunnel ventilation
  • Replacement of tunnel fire main
  • Tunnel Plant Monitoring & Control System (SCADA system)
  • Video Incident Detection system (VID)
  • Maintenance and upgrading of tunnel drainage and pumping equipment
  • Radio Re-Broadcast System
  • Tunnel Public Address System
  • Motorway communications hardware upgrades: CCTV, MIDAS, traffic signals, emergency roadside telephones and NRTS longitudinal communication cables
  • Building services: Intruder alarm, fire alarm, fire suppression, local CCTV, maintenance telephones and access control
  • Temporary HV and LV power distribution and site setup
  • Temporary tunnel safety systems: SCADA, gas monitoring, public address, telephones and ventilation