Rising sinkhole threat puts India's infrastructure at risk during monsoon

In Ahmedabad, Gujarat, a sinkhole formed when a road collapsed during heavy rainfall in the Shela area on June 30, 2024. Social media videos captured the road caving in and water gushing into the cavity. There is a growing concern about the increasing sinkhole frequency and severity in India's urban areas.

In another incident, on June 29, 2024, a sinkhole was formed on the KG Halli-Nagawara Road in Bengaluru due to Metro tunnelling work. In March 2024, Lucknow saw a massive sinkhole nearly swallow a car after heavy rain. In December 2023, there was a seven-foot deep and 10-foot wide sinkhole on one of Bengaluru's busiest roads. Chennai faced a road cave-in that swallowed a transformer during heavy rainfall triggered by Cyclone Michaung in late 2023.

These incidents reveal issues with India's urban infrastructure during the South Asia monsoon season. The cities like Ahmedabad, Gandhinagar, Chennai, and Bengaluru faced disruptions due to waterlogging, flooded underpasses, and impassable roads due to sinkholes. The Chennai airport shut down after heavy rainfall.

Why do sinkholes happen on roads?

Sinkholes are common in urban areas, especially during monsoons, posing risks to public safety and causing traffic disruptions. Understanding the causes is crucial for prevention and mitigation. The United States Geological Survey defines a sinkhole as a ground depression without natural drainage.

Dr Sanjay Sharma, a geotechnical engineer at the National Institute of Technology Rourkela, told Ground Report,

"Sinkholes are a type of subsidence, occurring when the ground goes down due to material removal from below, creating a cavity and causing the land above to subside."

Water infiltration can come from sources like leaking underground water pipes or sewage lines, eroding the soil and creating cavities beneath the road. Heavy rainfall, like during monsoon seasons, worsens the problem as water levels rise and flow increases. When buildings are constructed, the soil is compressed to make it stable and sometimes groundwater level is lowered to prevent soil settlement. While roads usually only compress the top layer of soil. Water and sewage lines often run beneath roads, and leaks from these pipes can weaken the soil. Over time, increased vehicle traffic and vibrations further weaken soil which leads to sinkholes. 

So, several factors can contribute to this, but the main issue is that the ground underneath can’t support the weight of the road. 

• If the soil isn’t properly compacted, it gradually sinks.  

• Mining or digging underground can weaken support structures. 

• Old or weak infrastructure may not be able to handle the weight of the road or the traffic passing over it. 

Dr Sarah Qazi, a Hydrogeologist expert and Faculty member at Kashmir University's Department of Earth Sciences, told Ground Report, 

"Sinkholes form over thousands of years as rainwater, slightly acidic from atmosphere and soil, erodes soluble rocks, creating underground cavities and caves. As these cavities grow, the ground above becomes unstable and collapses, forming a sinkhole."

However, she said, in urban areas, human activities cause more collapses. She added,

“Sinkholes are complex geological phenomena caused by natural and human-induced factors. They are depressions in the Earth's surface caused by ground collapse, often due to karstification, where water dissolves rocks like limestone, dolomite, or gypsum”.

Sinkholes are common in urban areas, especially during monsoons, posing risks to public safety and causing traffic disruptions. Understanding the causes is crucial for prevention and mitigation. The United States Geological Survey defines a sinkhole as a ground depression without natural drainage.

Water infiltration can come from sources like leaking underground water pipes or sewage lines, eroding the soil and creating cavities beneath the road. Heavy rainfall, like during monsoon seasons, worsens the problem as water levels rise and flow increases. When buildings are constructed, the soil is compressed to make it stable and sometimes groundwater level is lowered to prevent soil settlement. While roads usually only compress the top layer of soil. Water and sewage lines often run beneath roads, and leaks from these pipes can weaken the soil. Over time, increased vehicle traffic and vibrations further weaken soil which leads to sinkholes.

Ageing infrastructure causes urban sinkholes

The Hefei University of Technology study found that the deterioration of underground infrastructure is a common human-induced cause of city sinkholes. Leaking water mains, sewer pipes, or stormwater drains can erode the soil, creating voids that lead to surface collapse, especially in older cities. These incidences are increasingly common, and they are often related to aged infrastructure.

The construction can trigger sinkhole formation. Excavation, drilling, and heavy machinery disturb the soil and create pathways for water infiltration. Improper fill practices can lead to settling and collapse. Another study showed that natural processes, like chemical weathering, cause sinkholes, while human activities like groundwater extraction and construction can worsen them.

The study identified three types of sinkholes: solution, cover-collapse, and cover-subsidence, each with distinct formation mechanisms and hazards. It explored their impact on flora, fauna, water flow, and biodiversity.

The research highlighted the economic impact of sinkholes, including property damage, reduced land values, and infrastructure disruptions. It stressed the need for early warning systems, land-use planning, and community awareness to mitigate sinkhole risks.

Metro tunnelling poses sinkhole risk

The Bengaluru sinkhole in Bengaluru was caused by Metro tunnelling work. Dr. D Paramesha Naik, a geo-environmentalist and Assistant Professor at the Department of Environmental Sciences at Bangalore University, warns of the threat sinkholes pose to infrastructure projects like Metro Reach-6 connecting Gottigere to Nagawara.

According to a study by the International Society for Soil Mechanics and Geotechnical Engineering, metro tunnelling poses unique sinkhole risks compared to roads, involving compressed soil and altered groundwater levels. Underground leaks from pipelines exacerbate soil instability. Metro tunnels use specialized EPB machines prone to settlements or sinkholes if not managed well. 

"Karst topography, excessive groundwater extraction, and construction have caused road cavity," says Dr. Naik. "Water and sewer lines are at risk due to heavy vehicle movement. Bengaluru Metro Rail Corporation Limited (BMRCL) and BWSSB should collaborate, conduct a joint survey, and proceed with tunnelling."

Dr. Niak said, 

"Before starting the Metro or any big project in Bengaluru, Mysuru, and Southern Karnataka, there should be a comprehensive geophysical survey to understand the water, soil, weather zone, and hard rock, which could span 30-40 km. He adds that fractures in hard rock due to internal dynamics can cause sinkholes and road cave-ins, with a relatively low impact in Bengaluru".

Climate change intensifies sinkhole risks

In an April 2024 study, researchers warned that climate change could exacerbate the sinkhole problem. Intense rainfall, more frequent due to climate change, can cause rapid changes in groundwater levels and increased erosion, leading to more sinkholes. The link between extreme weather and sinkhole formation is becoming clearer. Heavy rainfall saturates the ground, increasing water pressure in soil and rock formations, speeding up erosion and destabilizing areas.

Another concern is long-term damage to buildings. Ground destabilization can lead to costly repairs or render buildings uninhabitable, even if not directly affected by a sinkhole.

Dr. Sarah said, 

“Sinkholes are unpredictable and dangerous. The sudden formation can collapse a road or land, endangering lives and property."

According to the USGS website, sinkholes are a hazard to property and human safety worldwide. Sinkholes pose economic challenges beyond safety risks, as repairing damaged infrastructure costs millions. Road collapses cause traffic disruptions, congestion, longer commute times, and reduced productivity for businesses in affected areas.

Preventing and mitigating sinkholes

Dr Sharma stressed the need for cities to invest in regular maintenance of underground pipes and drainage systems. Advanced monitoring techniques, like ground-penetrating radar, can help identify potential sinkhole areas.

Preventive measures include ensuring sound sub-structures before construction, monitoring and maintaining drainage pipes and sewers to prevent or fix leakage, using best building practices, and removing soluble rocks like limestone to prevent cavities and road sinking.

Recognizing warning signs of a potential sinkhole is crucial for public safety. Look out for cracks in the ground, unexplained depressions, tilting or falling trees or fence posts, and rapid ground hole appearance. On roads, new surface cracks or crumbling shoulders could indicate a developing sinkhole."

USGS notes, “Sinkholes are dramatic because the land stays intact until the underground spaces become too big. The subsidence rate poses a significant potential risk to public safety.”