Works to repair a sinkhole that opened up in St Albans a year ago is expected to be finished by Christmas, according to Hertfordshire County Council.
In the early hours of 1 October 2015, a hole measuring 12m wide and 7m deep opened up in Fontmell Close cutting off gas, electricity and water supplies, and preventing access to 52 properties.
The council said that the initial response focused on making the area safe. It has since been working with its highways contractor, Ringway, to fill the hole with concrete to stabilise it and prevent a further collapse.
The council said that it had been working on a number of in-depth investigations to find a permanent solution to the problem. It has carried out a full microgravity survey and undertaken exploratory drilling to examine the ground beneath the road to establish the cause of the hole and, more importantly, if there were further issues that needed to be addressed.
The investigations found that the most likely explanation for the cause of the collapse was a chalk excavation in the bedrock beneath an historic clay pit on which the area was built.
However, the council said that work to reconnect the utilities to affected homes and subsequently reinstate the road could only begin when it had gained a complete understanding of the ground beneath Fontmell Close and neighbouring Bridle Close, and established that there was no further cause for concern.
Hertfordshire County Council also carried out investigative work on the lower field behind the houses where a temporary road was established, and St Albans City and District Council investigated parts of the recreation area at Bernards Heath. It said that neither area had shown cause for concern.
“It was essential that we established the cause of the collapse before we started repairs. The safety and peace of mind of the residents was a prime factor,” said Hertfordshire County Council cabinet member for highways Terry Douris.
“I have been impressed by the considerable cooperation amongst all of the utility companies.”
Douris said that Thames Water had rebuilt its sewers in August, which allowed Ringway to bring the road up to foundation level ready for the other utilities. Affinity Water has also completed its repairs and has now handed over the site to National Grid to re-establish the gas supply.
UK Power Networks is set to restore electricity within the next two weeks, and BT and Virgin are then scheduled to complete the utility works, laying phone and cable television connections. Douris said that once these works are complete the roadway and pavements can be finally reinstated.
“This has been an extremely stressful time for the residents and it would be wonderful if they can be safely back in their homes for Christmas,” said Douris. “If all goes to plan, we will do everything we can to have the road re-opened by then, and we hope householders and their insurers can reach agreements to allow them to return home.”