Clay Technology magazine
7 Jun 2019

A mass of concrete weighing a record-breaking 105 tonnes was found under the streets of London. Shardell Joseph reports.

‘Concreteberg’, a 105 tonne (t) and 100m-long concrete mass, was found in a London sewer as a result of the material being poured down the drain. The mass has blocked three Victorian Era sewers under Hall Street, Islington.

According to Thames Water, it is the largest mass of concrete the company has ever seen – it could take up to two months to remove and cost up to £150,000. To tear the concrete apart, work will take place at the junction of Goswell Road and Hall Street in Islington, and is likely to cause traffic disruption.

‘Normally blockages are caused by fat, oil and wet wipes building up in the sewer but, unfortunately, in this case it’s rock-hard concrete,’ said Thames Water Operations Manager Alex Saunders. ‘It’s in there and set to the Victorian brickwork, so we need to chip away at it to get it removed,’ he said.

Caused by concrete dumping, Thames Water claims the money needed could have been spent on important matters such as investing in the network and helping customers in vulnerable circumstances. To remove the hardened mass, a range of cutting tools will be used, including jackhammer pneumatic drills and high-pressure jets.

Local residents were informed of preparatory work that started at the beginning of May. Tankers are also on standby to pump out waste 24 hours a day to protect the environment, and ensure nearby properties are not flooded with sewage caused by the blockage.

‘This is not the first time damage has been caused by people pouring concrete into our sewers but it’s certainly the worst we’ve seen,’ said Saunders. ‘It’s very frustrating and takes a great amount of time and effort to resolve. We’re now doing everything we can to deal with it as quickly as possible, making sure our customers don’t have to suffer because of this mindless abuse of our network.’

An investigation into the source of the concrete is currently underway, w ith Thames Water hoping to recover some costs from the culprits.

Maintaining the London sewers

London sewers are an impressive example of Victorian engineering, with an operational life expectancy of 500 years. However, with a growing population and the shrinkage of green spaces – absorbing the rainwater – greater demand has been placed on the ageing sewers.

Each year, more than 15 million people in London and the Thames Valley flush or drain 2.8 billion litres of used water for treatment, and Thames Valley clears around 75,000 blockages from the sewers. A combination of the greater demand and irresponsible disposal of materials has created huge challenges to the sewage system over the years.

In 2017, a 130t mass of unflushable debris described as ‘fatberg’ was discovered under Whitechapel in London, made up of congealed fat, wet wipes, nappies, oil and condoms which had accumulated over the last few years.

In the same year, emergency roadworks were sparked in south London after a rogue builder irresponsibly tipped concrete into a sewer, which caused a block 10m-long. With this smaller amount of concrete, workmen were forced to completely replace the pipes it destroyed.

Last year, Thames Water was called to clear 42,000 blockages caused by fat and non-biodegradable matter, a 6% increase on 2017, and the company spends £18mln every year clearing blockages from its sewers. The water industry is taking steps to educate the public on what can and cannot be flushed in its fight against sewer blockages. Earlier this year, Water UK created a ‘fine to flush’ symbol to help consumers identify products, such as wet wipes, which can be safely flushed.

Thames Water has pledged to invest heavily to improve the network and increase monitoring as part of its business plan for 2020-2025, expecting to use up to 200,000 new sewer depth digital monitors.