Horizontal directional drilling used to install 33kV cables under London in £7M project

UK Power Networks (UKPN) has installed 9km of 33,000V cross-linked polyethylene cables under tramlines, railway and roads in South London, by using horizontal directional drilling (HDD). The £7M cable replacement project from Sydenham Park to Churchfields, in south London, was designed to upgrade electricity infrastructure and improve the reliability of power supplies. UKPN said a horizontal directional drill was used to “pave the way for the most significant part of the route”, which included going under railway and tramlines at Avenue Road Station. The HDD carved a 50cm tunnel to house cables that were installed under the railway and tramlines, while passenger services continued as normal. The power company described HDD as “a specialist technique that allows cables to be installed safely beneath railway infrastructure without the need for major roadworks”. It added: “By using an underground bore, the method helps reduce disruption for passengers, road users and the local community.” Ramboll lists benefits of HDD over other tunnelling techniques including “reduced environmental impact”, because “quicker, less intrusive construction reduces fuel consumption and carbon emissions compared to cut-and-cover.” However, it also lists a series of limitations, such as “risks associated with frac-out and borehole collapse”. It adds: “Frac-out is when the bentonite slurry that is used to stabilise the borehole escapes into the ground due to weak or fractured soil, or excessive slurry pressure. “This can have [an] environmental impact due to contamination and cause delays to a project.” UKPN said the project supports its “commitment to environmental stewardship, aligning with the Groundwater Regulations 2009 and industry standards”. In addition to the HDD-enabled cable replacement, the project also includes “the installation of spare ducts to future-proof the network and facilitate further upgrades,” it said. The cable upgrades project between Sydenham Park and Churchfields is “closely coordinated” with the £20M Beddington to Sydenham 132kV project, “maximising efficiency and minimising disruption for residents and businesses,” UKPN added. UK Power Networks project manager Jason Callaghan said: “We’re installing modern cross-linked polyethylene cables, futureproofing the network and delivering a more resilient supply for our customers. “The main driver for the project is to upgrade the cable circuits between Sydenham Park and Churchfields; it’s a major step forward for local network reliability. “There has been close liaison with Transport for London, Network Rail and the council, to carry out the HDD effectively.” UK Power Networks portfolio manager Claire Sheridan said: “We’re investing around £30M to replace 132,000V and 33,000V cables between Sydenham Park to Churchfields and Beddington to Sydenham. “It’s an extremely busy route with lots of other utilities’ equipment underground, and above ground we are squeezed between residential streets, tramlines and an active railway.” She added: “The HDD is a complex engineering operation that keeps the trains running and the streets open while the works take place. “First, we drill a small pilot hole, then we progressively widen it four times in order to achieve the correct diameter to pull the ducts through. We pulled the ducts through beneath the railway, keeping a safe distance from homes and track.” McCormack Drilling spokesperson Fintan McCusker said: “This was a challenging project given the tight suburban location, railway infrastructure, and utilities to be negotiated by HDD. “Our team worked closely with UK Power Networks and Clancy to develop a workable solution to the many engineering challenges at this location. “It required meticulous attention to detail right through from feasibility, design, planning through to installation.” Savills Utilities and Infrastructure team client delivery lead Richard Fisher said: “Working alongside UK Power Networks Major Projects Consents and Stakeholder Engagement teams in a complex urban environment, Savills Land Assembly and Building & Project Consultancy teams provided a suite of services to support the successful delivery of this project. “Close coordination between teams across UK Power Networks, Savills, and delivery contractors was essential in securing the necessary consents and maintaining relationships with stakeholders throughout the project.” A report commissioned by the Department for Energy Security and Net Zero (DESNZ) and produced by Ramboll, published in June 2026 titled RAF021/2425 Study of the Potential for Cost Reduction in Undergrounding Transmission Lines over Long Distances described HDD as “a trenchless construction method that can be used to install cables or conduits without the need for extensive excavation”. “The drilling rig […] is set up at the surface without the requirement for a shaft or pit to launch from, and a small diameter pilot hole is bored along a pre-determined path, it said. “HDD has become a prevalent method for installing underground crossings for cables within the industry in the UK and globally. HDD has been used to install cables in the ground with voltages from 132kV (AMS, 2024) up to 400kV.” Like what you've read? To receive New Civil Engineer's daily and weekly newsletters click here. Have your say or a new account to join the discussion.