Project Overview

Following the successful delivery of the Bank Station Capacity Upgrade with Dragados, Joseph Gallagher’s tunnelling expertise was once again called upon - this time at the heart of one of the UK’s largest infrastructure projects.

Our team was commissioned to construct a new tunnel beneath the HS2 construction site at Euston Station, providing a crucial connection between a new traction substation (TSS) and the London Underground network.

With over 40 years of specialist experience and an award‑winning reputation in complex tunnelling and infrastructure works, Joseph Gallagher continues to help deliver vital upgrades across the UK’s transport network.

Scope of Work

The works involved sinking an 8m internal diameter shaft, belling out to 10m ID, to a depth of 20 metres using a combination of segmental lining and SCL (Sprayed Concrete Lining) techniques.

This shaft connected two newly constructed 6.5m diameter SCL tunnels totalling 100 metres in length. The alignment required exceptional precision, threading the new tunnels between multiple critical live assets including:

The operational Northern line tunnels directly below
A high‑voltage electricity tunnel
A major water main

Working within one of the most congested underground environments in London required meticulous planning, advanced engineering, and strict control measures.

Challenges & Innovations

Bespoke Travelling Shutter System

One of the most significant engineering challenges occurred during the secondary lining works. Due to restricted space within the tunnels, a traditional shutter system was not feasible.

To overcome this, our team designed and implemented a bespoke travelling shutter that allowed:

A section of the crown to be cast, struck, and wheeled forward
Rapid repositioning without dismantling the shutter
Achieving an impressive three‑day pour‑to‑pour cycle

The shutter was fabricated in three modular parts, pre‑assembled at pit bottom, and transported into the tunnels. This modular approach also enabled us to negotiate tunnel curves by moving sections individually and reassembling them in position.

Overcoming the National Steel Fibre Shortage

During construction, the UK experienced a steel fibre shortage - heightened by COVID‑19 impacts and global supply chain disruptions, including the 2021 Suez Canal incident.

To maintain programme delivery, Joseph Gallagher proposed and implemented an alternative structural design, replacing fibres with steel reinforcement mesh and applying SCL in two layers. This solution was fully approved and executed without compromising tunnel integrity or safety.

Outcomes

The project delivered the first SCL works on the entire HS2 programme, marking a significant achievement for both HS2 and Joseph Gallagher.

The team successfully broke through into the 117‑year‑old Northern line tunnels, constructing a precisely aligned radius tunnel to meet existing cast‑iron linings. Works were completed safely within the live LU environment, including core‑drilling and controlled breakout of a brickwork wall to exact specification.