18km Fibre in Sewer Installation, London’s West End


JSM was appointed to provide a fibre in sewer (FiS) solution for our client involving 3 different network operators.  3 x 144f, one per operator, connected to two West End of London Exchanges.




11 Months

Date Completed

October 2019

This project referred to as “Project Montana” in the heart of Mayfair was divided in a North and South Route involving the construction and connection of 85 breakout chambers for future customer connections. The overall route was approximately 18km long with the same start and end points: Mayfair BT exchange to Gerrards BT Exchange.


JSM had early engagement with the client and their appointed designers to identify the most cost effective and practical routes, using the Thames Water sewer networks as a starting point.


Whilst not principal designers, JSM assisted and advised throughout the early design stages, offering advice and expertise where required.

Local Authority Engagement

Discussions with local authority to plan the best approach to permitting the works for the sewer breakout locations.

Thames Water Liaison

Work closely with waste water operator to gain access to the sewer network in a safe planned manner.

Key Project Deliverables

  • Civils installation

JSM constructed 85 chambers within the West End in popular areas including Soho, Mayfair, Piccadilly, connecting them all to the sewer network.

JSM Streetworks Department obtained all necessary licences and permits from relevant London Borough of Westminster and TfL to suspend bays, close or divert roads to carry out civils works as necessary;

Options were explored if trial holes revealed congestion including moving the chambers from footway to carriageway or vice versa, slewing the chambers or proposing a redesign to the client;

A number of Section 58 issues were managed efficiently to avoid delaying the programme for example in Maddox St, Baker St. Reinstatement of  a wide range of surfaces including Chinese setts, cobblestones;

  • Cable installation and Jointing

JSM Installed a total of 72,400m of 144f cable with 224 joints for 3 operators including 54no 144f joints, 26no prep/loop spur joints; 102no prep/loop joints; 144f cable install diverse;  and the 144f terminations into 2 BT exchanges in Mayfair and Soho.

  • Testing 

Bi-Directional testing of 3 main 144f core cables at 1310, 1550 & 1625.

  • Customer Connection

From new chambers install route for cables to access building premises, creating new building points as required.

  • As Builts and hand over

Video survey of sewer installation, photographic record of every chamber installed. CAD as built drawings for subduct in sewer and all chambers. Detailed duct space records for each chamber identifying each cable for each of the operators. Fibre test results in 3 different formats to satisfy the needs of each operator.

Services Provided

  • Surveys
  • Design Advice and Support
  • Project Management
  • Stakeholder Management
  • Site Supervision
  • Excavation
  • Chamber Construction
  • Installation
  • Reinstatement
  • Splicing & Testing
  • DSRs
  • As Builts
  • Video footage of completed sewer installation