Chiswick High Rd void filled, but why are sinkholes becoming more common?

Image above: Cycleway 9 roadworks at the Cranbrook Road/Chiswick High Road Junction

‘Void’ filled in and Chiswick High Rd reopened

The void which road workers discovered under Chiswick High Rd at the junction with Cranbrook Rd has been filled in and the westbound carriageway has been reopened.

Councillor Katherine Dunne, Deputy Leader of Hounslow Council and Cabinet Member for Climate, Environment and Transport Strategy, told The Chiswick Calendar:

“We are pleased to announce that Chiswick High Road has now fully reopened, following the completion of repairs to the void.  We apologise for any inconvenience caused to residents in the Chiswick area.”

This is the second time in four months a hole has been found and repaired as an emergency.

In June a sinkhole opened up outside Turnham Green tube station, resulting in the closure of Turnham Green Terrace for several days while engineers from Thames Water investigated.

It was reported to be 20 ft deep, though the opening in the road surface was quite small. On that occasion the engineers, working with Hounslow Highways, mended a broken sewer and filled the hole.

The hole beneath the surface at the end of Cranbrook Rd was discovered by roadworkers installing new infrastructure for cyceway 9. We asked Cllr Dunne the cause of the void.

“Unfortunately we would be unable to say what caused the void” she said, “or speculate on whether the road has any other voids. However, in partnership with Hounslow Highways, we are monitoring the road closely and will provide further updates if needed.”

Our request for an interview with Hounslow Highways’ chief engineer was turned down.

One sinkhole is unusual, but two holes under the road discovered within four months invites the question why is this happening and whether we are likely to find more.

Are there ways we can find out about holes under the road before the road surface collapses or roadworkers just happen across them by chance, or do we just wait until there is a serious accident?

Images above: Dr Kourosh Behzadian, Thames Water works on Turnham Green Terrace in June 2022 after a sinkhole appears 

Why do sinkholes happen?

We spoke to two academics to try and shed some light on what is happening underneath our roads.

Dr Kourosh Behzadian, Course Leader of BEng and MSc Civil Engineering at University of West London, told The Chiswick Calendar there were two possible reasons why sinkholes happen in built-up urban areas like London:

“The possible reason could be because of man-made reasons of pipeline leakage. Or, it could be natural groundwater or soft-surface flow movement.

“We can’t just say all the time the reason is because a pipe-line has burst. It could be, for example, a spring – which would cause a lot of issues because of heavy rainfall.”

Thames Water admitted in August it is losing more than 600 million litres of water a day through leakage. That is almost a quarter of all the water it supplies.

When the Turnham Green Terrace sinkhole opened up the weather had been hot and dry for weeks. If a sinkhole occurs when there hasn’t been heavy rainfall for weeks, it is more likely the issue one of pipes leaking, Dr Behzadian told me.

“If the leakage has been running for a long time, and washing all the soils and sediments away, it could cause a larger hole.”

Highway maintenance teams usually can find out what has caused a sinkhole, he said, though sometimes it was difficult to find the cause with any certainty.

Thames Water say they are fixing more than 1100 leaks every week, but they have 20,000 miles of pipes, some of them dating back to the Victorian era – 60% were laid more than 60 years ago; the oldest are more than 150 years old.

They have teams out trying to detect leaks. John Joe Healy Matthew, a reduction supervisor for Hydrosave, the contractor that handles Thames Water’s leak detection in north London, told Wired magazine:

“The majority of leaks you’re never going to see. Big leaks that fill streets with water and send people stripping supermarket shelves of bottled water make headlines, but the real damage happens below the surface.”

Image above: Roadworks at the junction of Cranbrook Rd and Chiswick High Rd

Sinkholes a regular occurrence now in London

There have been some spectacular sinkholes recorded recently in the South East of England. A lorry fell into a sinkhole in Wokingham at the beginning of October when a sewage pipe collapsed.

Around 50 properties were damaged in north London in August when a burst water main caused flooding three feet deep and two sinkholes opened up, prompting local MP Jeremy Corbyn to say:

“Thames Water are not investing enough in their infrastructure. They do not want to invest the money. The amount of water wasted each year will fill Loch Ness.

“I think it’s time we gave up on privatisation and brought it back under public control. They are not responsible, the water companies.”

A sinkhole spanning the whole width of a residential street opened up in Bexleyheath in June. This one measured approximately seven metres by seven metres and was four metres deep. A car just stopped in time from falling into it. A motorcyclist tried to jump it and failed, losing his bike in the process, and running away, according to witnesses.

What could be done to proactively detect sinkholes?

We also spoke to Dr Muhammad Naveed, an Associate Professor of Civil Engineering also at University of West London, who said there are various methods highway maintenance teams could use to locate more sinkholes in the area.

“Locating sinkholes and subsidence without digging, probing, or drilling can be accomplished using non-destructive field surveys. Various geophysical investigation techniques can be used including ground penetrating radar, electrical conductivity, electrical resistivity and seismic velocity measurements.”

He added that there were a number of ways to fix and prevent sinkholes, including:

  • Preventing water withdrawal and the decline of the water table
  • Using efficient drainage systems and diverting surface runoff
  • Remediating sinkholes and clogging swallow holes
  • Filling cavities in the soil or rock by grouting
  • Improving the ground by compaction or injection grouting to increase the strength and bearing capacity of the soils

The Chiswick Calendar has approached Thames Water for comment about water mains leaks in the area and will ask the Council again what they are doing to find sub-surface holes before we fall into them.

Read more stories on The Chiswick Calendar website

See also: ‘Void’ discovered beneath Chiswick High Rd

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