Delivering Innovation

The scope of works involved decommissioning 40% of the bridge from the base, excavating and drilling the structure to remove a section of the bridge, in order to create space for a new culvert. Prior to the partial demolition of the bridge, the existing three-span bridge was filled and the vast variety of services and utilities within the bridge had to be diverted, including a large volume of EHV (Electrical High Voltage) circuits and telecom utilities belonging to multinational corporations such as Vodafone and BT. 

FM Conway were also commissioned to divert a Thames Water main, a one-metre diameter pipe that ran north-to-south on the east side of Lisson Grove bridge, which supplied water to over 250,000 residents of London each day. As previously mentioned, this was achieved by the construction of a reinforced concrete culvert structure located between the decommissioned bridge and proposed residential building.

Ismet Sakajani, Contracts Manager at FM Conway, explains:
“The culvert had to be extended on either end of the bridge using a piled wall structure, comprising 20-22 metres deep and 1 metre diametre piles, as well as ground anchors to maximise the strength of the ground and retain the highway embankment."
 

Ismet continues: “The section immediately adjacent to the bridge segment included twin contiguous piled walls, connected by a base slab acting as a permanent prop. The passive ground anchors installed within the piled wall were mounted at two levels to limit the overall deflection of the culvert, following the building excavation on the east side. The anchor heads rest on a wailing beam which spans across the front of the piles, above the slab level”.

In order for the Thames Water main to be completely diverted, two thrust blocks were built on each bending of the bridge, supported by a base slab and pile wall. The remaining length of the structure in continuation of the south thrust block included a piled wall with ground anchors positioned at different levels. 

Ismet summarises: “This proposed structural arrangement was chosen to limit the ground movement following the building excavation, with the objective of protecting a Cadent gas main and the Thames Water main." 
 

Challenges and Solutions 

Due to the location of the project, careful planning was critical to ensure the works were delivered safely within a high-profile location, minimising our impact on residents and members of the public alike. This was achieved through constant communication with residents, businesses and the wider community through FM Conway’s Public Liaison Officer, ensuring stakeholders were informed ahead of the works, with additional signage displayed around the local area to ensure those affected could plan to minimise disruption. 

The site team had to ensure they were extra careful throughout the project to avoid damaging the live utilities and to preserve the safety of those working on site. Due to the fragility of the gas main – 60 tonne restriction - FM Conway’s structures team developed bespoke temporary bridges to facilitate the movement of plant and materials on site. Whilst diverting the gas main, the team developed a temporary rider around the site to inhibit the flow of gas within the live gas pipe, enabling the continuing of work in gas-free conditions.