How soil behaviour shaped destruction and why geotechnical insight is key to earthquake resilience.
Introduction
On 28 March 2025, a powerful magnitude 7.7 earthquake struck central Myanmar near the cities of Sagaing and Mandalay. The shallow depth of the quake led to strong surface shaking, causing widespread structural damage and tragic loss of life both locally and in distant regions such as Bangkok, over 1,000 kilometres away.
While the immediate focus was on the visible devastation, an equally important story unfolded beneath the surface. The way soils responded, whether by amplifying seismic waves, liquefying, or shifting unevenly, played a decisive role in the scale and distribution of the damage. This event highlighted that earthquakes are not just geological events, but geotechnical ones too.
In Mandalay and Sagaing, areas built on soft, water-saturated soils suffered the most, with building collapses, road fractures, and infrastructure failures such as the collapse of the historic Ava Bridge. Meanwhile, in Bangkok, local ground conditions amplified the distant tremors enough to topple a 33-storey building under construction.
The 2025 Myanmar earthquake demonstrated once again that understanding soil behaviour is critical to protecting lives and infrastructure, not just where a quake strikes, but across entire regions.
The Ground Beneath – Soil Behaviour and Failures
This earthquake vividly demonstrated that soil isn’t static; it plays an active, sometimes destructive, role during seismic events.
1. Liquefaction in River Plains
Central Myanmar is home to wide alluvial plains, particularly around the Irrawaddy River. These consist of loose, water-saturated sands and silts, prime candidates for liquefaction. When shaken violently, these soils temporarily lose their strength, behaving like a fluid.
Field and satellite evidence suggest extensive liquefaction occurred along the riverbanks, with sand boils, lateral spreading, and subsidence observed. Structures built on these weak soils often settled unevenly or tilted, while roads cracked and slumped.
2. Site Amplification in Bangkok
Bangkok is built on deep, soft clay. These conditions are known to amplify long-period seismic waves, especially from distant, large earthquakes. The 7.7 Myanmar quake radiated low-frequency energy that travelled through the Earth and was intensified by Bangkok’s soft soil basin, resulting in prolonged shaking that caused a 33-storey concrete tower to collapse entirely.
This phenomenon, soil amplification, meant the quake’s impact was far greater than would be expected based on distance alone. It’s a textbook example of how site conditions can magnify and extend the reach of seismic hazards.
3. Differential Settlement and Ground Rupture
Along fault lines and in areas with soft subsoil, structures experienced differential settlement, uneven sinking that can tear buildings apart. Roads in Naypyidaw and Mandalay displayed fissures and buckling. Historic pagodas suffered partial collapses, likely due to unequal movement beneath their foundations.
In other locations, surface rupture from fault movement sheared directly through roads and buildings, leaving long, visible ground cracks.
Lessons in Soil-Structure Interaction
Soil-structure interaction (SSI) is the dynamic interplay between the ground and the structures built upon it. This earthquake underscored several critical lessons:
1. Buildings React Differently on Different Soils
Structures on stiff ground or rock experienced far less damage than those on deep alluvium. In Mandalay, buildings on the floodplain were devastated; in slightly firmer zones, many stood firm. Understanding this difference requires proper geotechnical site investigations, including boreholes, SPTs, and CPTs, before construction.
2. Foundation Design Matters
Many buildings that failed had shallow foundations or were built on poorly compacted fill. Structures with deep pile foundations anchored in stable layers fared better. In liquefiable zones, shallow foundations can float, tilt, or collapse.
3. Structural Resonance
Tall buildings have natural frequencies. If the shaking frequency of the ground matches that of the building, resonance can occur, amplifying motion and leading to catastrophic failure. This likely contributed to the Bangkok collapse, where soft clay extended the shaking duration, and the building’s flexible flat-slab design couldn’t cope.
4. The Importance of Codes and Retrofitting
Many buildings in Myanmar were constructed without adequate seismic design. The event highlighted the need not just for better codes, but for enforcement, education, and retrofitting of existing vulnerable structures.
The Role of Geotechnical Engineering and Laboratory Testing
As this disaster has shown, what lies beneath our feet is just as important as what we build above it. Geotechnical engineering plays a critical role in:
- Identifying hazardous soils (such as loose, liquefiable sands or soft, compressible clays).
- Designing foundations that can safely interact with ground movements during seismic events.
- Predicting how soil layers will respond to cyclic loading and stress redistribution during earthquakes.
One of the key tools in achieving this understanding is laboratory testing. Geotechnical laboratories around the world use a wide range of advanced equipment to simulate and measure soil behaviour under controlled conditions. These include:
- Triaxial testing systems to assess strength and deformation characteristics.
- Cyclic and dynamic loading equipment to replicate seismic forces.
- Consolidation tests to evaluate compressibility and settlement potential.
- Advanced soil characterisation tools that provide data on stiffness, permeability, and pore pressure response.
This laboratory data forms the backbone of seismic soil analysis and informs foundation design, soil improvement strategies, and risk assessments for infrastructure in earthquake-prone regions.
When paired with field instrumentation, such as piezometers, inclinometers, and data loggers, engineers gain a complete picture of soil performance both before and after seismic events. Together, these methods support safer design, real-time monitoring, and more resilient construction practices worldwide.
Conclusion
The 2025 Myanmar earthquake was not just a tale of tectonics, it was a wake-up call about the ground we build on. From the liquefied plains of Mandalay to the swaying towers of Bangkok, soil behaviour dictated outcomes.
For engineers, planners, and policymakers, the lesson is clear: earthquake resilience begins with understanding the soil. Investing in geotechnical investigation, soil-aware design, and robust instrumentation isn’t just smart, it’s essential.