Deeper probes carried out around St Albans’ sinkhole site

More surveys are being carried out near St Albans' sinkhole, Fontmell Close, April 2016. Pictured ar

More surveys are being carried out near St Albans' sinkhole, Fontmell Close, April 2016. Pictured are, left, Emma Small, of Opus, and Richard Knight, highways operational officer at Herts county council - Credit: Debbie White

Specialised drilling equipment has again been a feature in a residential cul de sac, as the soil around St Albans’ sinkhole undergoes further investigation – 45 metres into the ground.

The Herts Advertiser visited the site in Fontmell Close last week as geotechnical experts, joined by utility services representatives, carried out further checks.

These included surveying beneath a concrete footpath which was damaged when the 12m-wide cavity suddenly appeared in the road on October 1, to ascertain stability of the subsoil.

One of the reasons for the further investigations is to establish whether there is a void deeper within the ground, as initial microgravity surveys along the road length last year highlighted areas of concern, and a potential anomaly, close to the site of the collapse.

Historic plans of the area show that a large clay pit was once located where Fontmell and Bridle Closes were later developed, and where the current collapse occurred.

Herts county council has conducted multiple surveys of the area, alongside private investigations organised by the insurers of some neighbouring homeowners affected by the sinkhole.

While the vast majority of residents in Fontmell Close returned to their homes some time ago, four households have been unable to do so, nearly seven months after the road collapse.

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A spokesman for the county council said: “Our engineers have now examined in detail the findings of the microgravity survey and exploratory drilling carried out under and next to the sinkhole in Fontmell Close.

“After cross-referencing these reports, we have identified an area under the highway where further investigation is required to form a more comprehensive picture of the make-up of the subsoil.

“A further borehole in the highway was drilled [last] week with work scheduled to be finished [this] week. Our priority will then be to analyse the soil samples as quickly as possible.

He added: “We have also commissioned investigatory works on the highway in the rest of Fontmell Close and in Bridle Close and expect to receive a report on those works shortly.

“We appreciate residents’ patience while we carry out this work. By ensuring we have the most complete understanding of the ground beneath Fontmell Close we will be able to take the best approach possible to reinstate the road in the long-term interests of residents.”