Erosion in tunnel under Kasaragod house still active; soil pipe extends beneath road: radar survey

Kasaragod: More than a month after an underground tunnel was discovered beneath Sadan K and Ramya’s house at Ottamavungal in Kasaragod's Kuttikol panchayat, scientists who inspected the property on Monday, September 14, found that the soil pipe is still active and that the erosion has extended beneath the road. They advised the family not to stay in the house until their detailed analysis is complete.

A team from the National Centre for Earth Science Studies (NCESS), Thiruvananthapuram, and the Federal Institute of Science and Technology (FISAT), Angamaly, scanned the property and its surroundings using ground-penetrating radar (GPR) in multiple directions to assess the extent and stability of the passage.

The survey indicated that the soil pipe extended from beneath the property towards and across the road, said senior NCESS scientist G Sankar, who led the team. Sankar is an expert in soil piping and has studied the phenomenon in Kerala’s highlands and foothills. He had also submitted recommendations in 2016 on measures to prevent soil piping-related disasters.

The team will analyse the GPR data on a computer before making a final assessment of the extent of the underground erosion, he said.

The scientists physically entered the passage and found that the soil pipe is about 72 metres long. It initially runs east-west and then turns north-south, beneath the house, before crossing the road and eventually discharging into a pond roughly 200 metres away, Sankar said. At one point, the underground cavity reaches about seven metres in height, giving an indication of the scale to which the subsurface erosion has developed.

Most significantly, the underground erosion, called soil piping, is still active. “When we were there, the ground was continuing to collapse. As you saw, water was also actively flowing underneath. So, we need to be more cautious," Sankar said.

He said the team did not find any immediate indication that the underground erosion had affected other houses. “At present, we don't see any problem with the other houses. The problem has started beneath the road. We will suggest a solution for that. But we need to analyse the data on the computer before making a final assessment,” he said.

Sadan and his wife Ramya invested around ₹30 lakh and nearly completed the house when they discovered the tunnel underground while digging a pit for the sewage tank.

Sadan, a tile mason, had undertaken much of the construction himself and had borrowed money, taken bank loans and sold Ramya's gold to finance the construction. The family had planned to move into the house on August 28, the day of Chathayam, but abandoned the plan after the underground passage was discovered.

The scientists have advised them to wait further. The GPR survey is only the first stage of the assessment. The team plans to conduct an electrical resistivity survey once the ground becomes dry.

Electrical resistivity surveying is a non-invasive method of investigating what lies beneath the ground by sending a small electrical current through the soil. The survey can help the scientists identify water-bearing zones, cavities and variations in the subsurface material and better understand the strength of the soil pipe.

The NCESS team will analyse the GPR results along with geotechnical inputs from FISAT's Panjami K, an expert in soil mechanics. "We will submit a report to the District Collector in two weeks before the electrical resistivity survey is conducted," said Sankar. The findings will then be forwarded to the Disaster Management Authority.

Sankar said the immediate purpose of the investigation was to determine the extent of the soil piping and assess whether the house and surrounding infrastructure could be made safe.

'Strict building rules needed'
The soil piping is not rare in northern Kerala. Sankar said soil piping has been observed extensively in Kasaragod, Kannur, Malappuram, and Kozhikode, besides Wayanad. “Therefore, when constructing houses or large buildings in such areas, we must first ensure that there is no such phenomenon beneath the site,” Sankar said.

He said the government may have to introduce stricter measures for foundation and structural design. "For instance, if there is hard rock underneath, we can construct the building by providing pillars that reach down to the hard rock. There are such methods available, and we may have to adopt them here in the future."

'People begin fundraising'
Irrespective of the scientific findings, residents of Kuttikol, under the leadership of panchayat president K Sobhana Kumari, have begun raising funds to help Sadan and Ramya build a new home.

A joint account operated by Sobhana, Sadan and convenor Madhusoodanan has received ₹7 lakh, just two weeks after the fundraising began.