HS2 (Bromford Tunnel)

Due for completion in 2033, the HS2 (High Speed 2) rail network is among the most significant building projects taking place in the UK. In 2022, WJ was contracted by the Balfour Beatty and Vinci joint venture to provide hydrogeology solutions towards the construction of an intermediate ventilation shaft at Bromford Tunnel, near Birmingham.

Location

HS2 (Bromford Tunnel), nr. Birmingham, UK

Client

Balfour Beatty and Vinci (joint venture)

Year

2022

Features

Tunnels | instrumentation plus monitoring

The ventilation shaft design

The shaft installation posed unique engineering challenges for WJ Groundwater’s hydrology experts because it required an effective solution to manage groundwater pressures within the mudstone layer, which may have led to basal heave during construction. The project required WJ’s meticulous planning as it would reside centrally between two tunnel bores that would connect to the train tunnels at track level.

The Bromford Tunnel’s intermediate ventilation shaft measured approximately 33 metres deep with a diameter of 19 metres. It had been constructed using diaphragm walling to ensure stability and featured a secondary inner lining along its lower portion. When connecting the shaft into the running tunnels, sprayed concrete lining (SCL) was applied.

WJ's groundwater control solutions

Within the shaft’s footprint, WJ installed an array of passive relief dual-purpose wells. These wells were integral in providing controlled flow paths to alleviate potential groundwater pressures effectively.

The dual-purpose design enabled active pumping offering additional capacity if the passive system proved inadequate under high-pressure conditions. The added functionality also allowed a flexible and robust approach to groundwater management throughout the excavation and construction phases of the project.

Real-time groundwater monitoring

In tandem with the groundwater control measures, WJ installed a series of fully grouted multi-level vibrating wire piezometers within boreholes across the shaft area. These piezometers provided crucial real-time data on groundwater levels and pressures for both WJ’s technical team and the client.

Utilizing WJ’s bespoke cloud-based monitoring portal, this data was accessible instantaneously, offering stakeholders a continuous overview of conditions. Such advanced monitoring ensured that any anomalies could be promptly addressed, therefore minimizing risks and delays. The combination of cutting-edge technology and WJ’s expertise ensured the success of the groundwater control and monitoring operations in this challenging environment. The dual-focus and holistic approach –preventative measures alongside real-time monitoring – exemplified the standard of engineering required for large-scale projects like HS2.

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WJ Groundwater has completed similar groundwater management projects in the UK and globally. Click on the links below to learn more about what we do.

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