At a glance

Godstone High Street in Surrey has reopened after 18 months of repairs following a major ground collapse caused by a burst water main and historic mine workings. Mainmark UK, part of a team appointed by Surrey County Council, used resin injection to strengthen the ground and prevent future collapses. The project highlights the growing risks of ground collapse in the UK due to ageing infrastructure and underground voids, emphasising the need for early investigation and remediation.

The reopening of Godstone High Street after an 18-month repair programme has brought one of the UK’s most complex recent ground collapse projects to a close. However, Mainmark UK warns that ageing infrastructure, water leakage and historic mine workings continue to contribute to ground movement and ground collapse risks across the country.

Final works have been completed in this Surrey village following the major collapse in February 2025, which created a hole 20 metres long, five metres wide and five metres deep. The collapse was initially linked to sandstone erosion caused by water from a burst water main. However, investigations later uncovered an underground mine network eight metres below the village, requiring extensive ground strengthening before the road could be reconstructed.

Mainmark worked as part of a multidisciplinary team appointed by Surrey County Council, carrying out resin injection works to strengthen weak and disturbed ground beneath the affected roads. Following remediation of the deeper mine workings by the wider project team, Mainmark carried out targeted resin injection between one and four metres below ground level to strengthen weakened and disturbed ground and address potential pathways for future void migration. Mainmark installed approximately 600 resin injection points across High Street and Salisbury Road during the three-week programme of ground improvement works.

Ground-strengthening techniques such as resin injection can be used to improve weak or disturbed ground while minimising disruption to surrounding infrastructure and communities. The works were supported by pre and post treatment Dynamic Penetrometer Testing, which confirmed measurable improvements in ground strength across the treated areas.

David Hedley, Infrastructure Lead at Mainmark UK, said: “Ground collapse events rarely have a straightforward cause. While damaged utilities can contribute to the formation of underground voids, investigations at Godstone also identified historic sand mine workings beneath the site, creating a more complex remediation challenge that required multiple ground engineering techniques.”

Mainmark has been involved in a growing number of projects across the UK where ageing buried infrastructure, leaking utilities and historic underground workings have created ground movement and collapse risks for highways, commercial assets and residential communities. “The challenge is that many of these risks develop silently over years or decades. By the time cracking, settlement or a road collapse becomes visible, the underlying problem may already be extensive.”

When a buried utility leaks, water gradually removes fine particles from the surrounding soil, creating a hidden cavity. Collapse occurs when the remaining ground can no longer support its own weight or the loads above it.

“Before repairs can begin, engineers must identify the root cause, assess ground conditions, understand any risks to nearby structures and protect live utilities. Depending on the complexity of the site, this process can sometimes lead to extended traffic restrictions while investigations, design work and remediation plans are completed.”

“The true cost of a sinkhole is not only the physical repair, but the disruption caused while communities wait for action,” David added. “The longer a void remains untreated, the greater the risk of further movement affecting roads, utilities and foundations.”

The Godstone project demonstrated how complex ground collapse incidents often require multiple remediation techniques working together. A layered ground engineering approach was adopted, with different techniques used at different depths to address specific ground conditions. Deep mine workings required remediation, while Mainmark’s resin injection strengthened the shallower layers beneath the road and helped improve the condition of disturbed ground above.

David said: “There is rarely a single standard solution. The priority is to identify the cause quickly and select the least disruptive, technically appropriate combination of treatments. “As underground assets age, local authorities and contractors must place greater emphasis on early investigation, accurate records and rapid ground-strengthening measures. That is how we protect homes, secure highways and help communities move again sooner.”

Established in the UK in 2016, Mainmark Ground Engineering (UK) Ltd is a subsidiary of the Mainmark group of companies.

Editorial insight

The completion of repairs to Godstone High Street brings a high-profile infrastructure challenge to a close, following a significant ground collapse in early 2025. The incident has drawn attention to the persistent risks associated with ageing underground assets, leaking utilities and the legacy of historic mining beneath many UK towns and villages.

While Godstone's experience was unusually severe, the factors behind it are not unique. Engineering firms and local authorities across the country continue to face similar, if less visible, risks as buried infrastructure ages and ground conditions change. For communities and businesses, the wider lesson is that ground movement can remain undetected for years, with disruption and repair costs escalating once problems surface. The Godstone project also highlights the need for early investigation and the use of a combination of remediation techniques to minimise disruption and restore vital routes safely.

Story ideas and journalist angles

Environmental/social impact

The Rising Threat of Ground Collapse in the UK: A Closer Look at Infrastructure Vulnerabilities

The increasing frequency of ground collapses due to ageing infrastructure and underground workings is a growing concern in the UK. This story explores the contributing factors, potential future risks, and the need for proactive measures from authorities and engineers.

Target audience who would cover this Story potential 8/10 Local/community

Impact of Extended Infrastructure Repairs on Local Communities: Lessons from Godstone

The extended repair period of Godstone High Street due to a sinkhole caused significant disruption. This piece examines the social and economic impacts on local residents and businesses, alongside the challenges faced by authorities in managing such projects.

Target audience who would cover this Story potential 7/10