Burst water main ‘probable’ cause of Surrey sinkhole, geologists say

Surrey County Council

GEOLOGISTS have said a burst water main is the “probable” cause of a sinkhole that led to the collapse of a road in a village in Surrey, southeast England.

Thirty households on the collapsed road in the village of Godstone were evacuated, with residents fearing they may not be able to return home for months. The sinkhole, first reported late on Monday night, had grown to 20 m in length by midday on Tuesday, by which point a “major incident” had been declared by Surrey County Council. The council confirmed yesterday that it is no longer growing.

The sinkhole is understood to have been caused by the ground underneath Godstone High Street becoming saturated with water. Late on Monday night, SES Water, the company that maintains the water mains in the area, reported a burst pipe underneath the road. Andrew Farrant, a regional geologist for southeast England at the British Geological Society, said: “It is probable that the sinkhole is due to a burst water main flushing out weak unconsolidated sands”.

He added: “Many recent sinkholes have been caused by collapses of old sewers or culverts,” including a similar incident in Storrington in West Sussex last October.

The exact cause of the sinkhole is yet to be confirmed, but Surrey County Council and SES Water have begun investigating. Farrant added that there were other possible causes such as an old, undocumented sand mine collapsing.

Phil Collins, a geology and geotechnical engineering researcher at Brunel University of London, said that the “cause appears to be the washout of soil from beneath the road as a result of a burst water main.

“This burst would have pumped a large volume of water into the soil in a short period of time, overcoming its strength and turning it to a slurry which was then washed away.”

SES Water confirmed on Wednesday that the burst pipe was repaired, and that no minor leaks had previously been reported from mains underneath Godstone High Street.

Network blockages

Initially, gas, electricity, and water were shut off to the homes that had to be evacuated due to the sinkhole.

A water industry engineer told TCE that the burst main could create sewage problems in the wider network, while sediment inside water pipes caused by the slurry could lead to flooding.

Carl Bussey, chair of the body set up by Surrey County Council to oversee the incident, said: “The site continues to be assessed by structural experts in order to manage the risk and understand what needs to be done.”

SES Water said they “continue to work closely with other agencies involved in this incident”.