St Albans sinkhole: survey machinery leaving site this week

Work continues to fix the damage caused by a sink hole in Fontmell Close

Work continues to fix the damage caused by a sink hole in Fontmell Close - Credit: Archant

Heavy machinery brought in to a residential street to conduct in-depth surveys of ground below and near St Albans’ sinkhole will be removed this week.

Protective hoarding was put around the 12-metre-wide cavity in Fontmell Close to allow engineers to take deep plugs of soil, to determine what lies beneath the road, the location of a former clay pit.

Peter Brett Associates have been at the site since mid-December, investigating subsoil conditions and checking the safety of the ground in the cul-de-sac after the road collapsed on October 1 last year.

Angled drilling has been carried out to explore what lies beneath four anomalies discovered in an initial survey at Fontmell and Bridle Closes, along with one at a nearby playing field used for emergency access.

These and other sites were pinpointed in an initial microgravity survey by Geotechnology Ltd consultants in October which showed a second, larger, cavity was potentially looming near the existing collapse, under neighbouring properties.

A spokesman for Herts county council said machinery used to drill 20 metre deep boreholes would be removed by the end of this week, with the findings to be analysed over the next few weeks.

Additional drilling will shortly take place under the corner of Seymour Road and under the portable building used by engineers in the street, which will also be removed.

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Four boreholes were drilled at the site of the sinkhole, which was nearly filled with a concrete plug immediately after the collapse.

But the county spokesman was unable to say how many boreholes were drilled at private properties, as those are being dealt with separately by loss adjustors.

A spokeswoman for St Albans district council said that although a temporary road had now been built on the playing field in Bernards Heath behind Bridle Close, residents’ vehicles had not been able to use it because of the further investigative drilling in the green space.

However this work should soon be completed.

A 4X4 shuttle service is still being provided in the meantime to transport people to and from homes and their cars parked nearby.