Dhaka has long expanded faster than it has planned. Wetlands have been filled, low-lying areas built over, and high-rises have been raised that may not withstand a major earthquake. In the first instalment of a six-part series, Star examines the city’s fragile ground, soil liquefaction, and construction gaps that could turn a powerful tremor into a disaster.
Residents across large parts of Dhaka face serious risks during a major earthquake, as much of the city stands on hazardous, liquefaction-prone soil, experts have warned.
They called for strict compliance with the Bangladesh National Building Code (BNBC), particularly proper piling and soil improvement, before buildings are constructed in high-risk areas.
A recent study by Rajuk and Buet shows that about 55-60 percent of Dhaka falls within the red and magenta zones of the city’s liquefaction hazard map, indicating highly vulnerable soil conditions.
“These areas also face high seismic amplification, as both hazards are linked to loose or artificially filled ground,” said Prof Mehedi Ahmed Ansary of Civil Engineering at Buet.
Within the 1,528 square kilometres under Rajuk’s jurisdiction, Buet researchers found that more than half the area is highly susceptible to soil liquefaction during a major earthquake.
Geologists said Dhaka’s soil profile, mainly red Pleistocene clay and soft alluvial deposits, is not suited to the city’s dense and largely unplanned expansion. A strong earthquake could therefore cause widespread structural failure.
Experts recommended proper piling and soil improvement, especially within the top five to six metres, in high-risk areas.
Buet classified Dhaka’s ground conditions into four colour-coded zones using the Liquefaction Potential Index. Red, with an LPI above 15, indicates the highest risk; magenta, with 10–15, indicates moderate to high risk; blue, with 5–10, indicates lower risk; and green, below 5, indicates the lowest risk.
Prof Ansary said red-zone areas could suffer severe ground failure during a magnitude 7.5 earthquake, particularly where groundwater levels are high, such as areas near ponds, canals and rivers.
Explaining seismic amplification, Ansary cited the 1985 Mexico City earthquake, where many mid-rise buildings collapsed despite the epicentre being 300 kilometres away because soft soil amplified the shaking.
“Sandy fill causes both liquefaction and amplification, while soft clay fill mainly causes amplification. Both are dangerous,” he said.
Large sections of Dhaka’s recent expansion near the Balu and Shitalakkhya rivers have been developed on sand-filled or reclaimed land, he added.
Construction in such areas is possible only with proper soil treatment, which developers often avoid because of the cost. Proper compaction can require up to ten times more material than loose filling.
“As a result, about 90 percent of Dhaka’s filled areas rely solely on piles without improving the surrounding soil, creating severe risk,” he said.
He cited the 2001 Kandla Port earthquake in India, where a building supported by 60-foot piles tilted by 15 degrees because the piles rested in weak, water-saturated soil.
On soil-improvement techniques, Ansary said methods such as cement injection, used at the Rooppur Nuclear Power Plant, can significantly strengthen sandy soil.
In typical filled plots where the fill depth reaches 40-45 metres, improving just the top five to six metres can substantially reduce earthquake shaking, he said.
Without treatment, both upper and lower soft layers remain weak, causing piles to bend and buildings to tilt during strong shaking, he added.
Echoing him, Md Zillur Rahman, former chairman of the Department of Disaster Science and Climate Resilience at Dhaka University, said only about 35 percent of Dhaka stands on strong red Pleistocene soil.
The rest consists of marshlands, floodplains, abandoned channels and low-lying basins, he said.
Neighbourhoods on Pleistocene terraces, such as Old Dhaka, Gulshan, Banani, Dhanmondi, the Dhaka University area, Khilgaon, Motijheel, Farmgate and Mirpur, benefit from relatively stronger soil conditions.
In some areas, including parts of Basabo, Badda, Uttarkhan and Dakshinkhan, red soil lies 10–20 feet below the surface, creating medium-quality ground conditions.
However, in floodplain areas near the Buriganga, Turag, Balu and Shitalakkhya rivers, red soil may lie 80-150 feet deep beneath thick layers of soft clay and recent fill, making construction particularly challenging.
Rahman said seismic waves can sharply amplify in former wetland zones, sometimes doubling in intensity. Building height must therefore be carefully designed to avoid resonance during earthquakes.
“You can build anywhere,” he said. “But the design must follow soil conditions. If guidelines are properly followed, severe damage can be avoided.”
Former Bangladesh Urban Resilience Programme project director Abdul Latif Helali said a soft-soil hazard map had been prepared, but Rajuk has yet to incorporate it into planning.
Rajuk’s Chief Town Planner Md Ashraful Islam said the authority received the map and planning proposals after the gazette notification of DAP-2022.
“It is under consideration. We will incorporate it when the DAP is updated,” he said.
Contacted, Liakat Ali Bhuiyan, senior vice president of the Real Estate and Housing Association of Bangladesh, said member developers follow the BNBC to reduce earthquake risks.
“The construction materials we use, including steel and cement, are produced with earthquake resistance in mind,” he said.
After the recent 5.7-magnitude earthquake, REHAB opened a control room and reported no damage.
However, he acknowledged uncertainty about the impact of a major quake. “The impact of a magnitude-7 earthquake is difficult to predict,” he said.
Red Zone areas include Hazratpur, Savar, Keraniganj, Narayanganj, Tegharia, Konda, Enayetnagar, Kashipur, Kalagachia, Narayanganj Pourashava, Bandar, Mugrapara, Narayanganj Sadar, Baktabali, parts of Mohammadpur and Dhanmondi, New Market, Lalbag, Madanpur, Dumni, Badda, parts of Pathalia, Ashulia, Kataballi and Darus Salam.
Magenta Zone areas include Konabari, Yearpur, parts of Harirampur, Biralia, Paurashava areas, Cantonment, Pallabi, Gulshan, Rupganj, Bulta, Khilgaon, parts of Kafrul and Dakkhinkhan, Adabor, Tejgaon, Rampura, Motijheel, Demra, Sabujbagh, Jatrabari, Kadamtali, Kadam Rasul Paurashava, Musapur, parts of Fatulla and Hazaribagh, Sadipur, Kachpur and Paltan.
