Active fault raises geotechnical questions for the Brahmaputra mega dam

Chinese geologists have warned that an active fault line beneath the planned Yarlung Tsangpo hydropower project could affect the structural stability of one of the world’s most ambitious dam schemes. The project is being built on the river known downstream as the Brahmaputra, before it enters India and Bangladesh.

The study focuses on the Paizhen Fault, a tectonic structure in the eastern Himalayas. Researchers reported that the fault has remained active since the Pleistocene and continued showing activity into the Holocene, with evidence of movement as recently as about 9,500 years ago. They also cited the 2017 magnitude 6.9 earthquake in Milin, Tibet, near the northern end of the fault, as evidence of modern seismic potential.

The concern is not only the dam itself. The researchers warned that the fault could affect nearby infrastructure including dams, roads, bridges, tunnels and reservoir slopes. In a project of this scale, geological weakness does not remain a local issue. It becomes a system-wide risk affecting construction, long-term operation and emergency planning.

The Paizhen Fault has fractured the surrounding rock mass and altered its mechanical properties. This can reduce foundation bearing capacity, weaken slope resistance and make engineering structures more vulnerable under seismic loading.

The terrain around the project has been described as having loose structure and weak cohesion. This is especially important for reservoir areas. Once a reservoir is impounded, long-term water immersion can reduce slope strength, increase pore water pressure and reactivate pre-existing weaknesses in soil and rock. When this is combined with earthquake shaking, the probability of landslides and collapses can increase significantly.

For a major hydropower project, reservoir slope instability can be one of the most serious geotechnical hazards. Large landslides into reservoirs can damage infrastructure, block access roads, affect water quality, generate impulse waves and threaten personnel and downstream communities.

This means that the key engineering challenge is not simply building a strong dam. It is understanding the whole geological environment around the dam, reservoir, tunnels, access roads and support infrastructure.

The researchers recommended stronger slope stability measures and retaining protections to reduce the risk of landslides and collapses during construction and operation. These measures may include slope reinforcement, retaining structures, drainage systems, rock bolts, anchors, protective barriers and continuous geotechnical monitoring.

In a seismically active mountain setting, design must account for both static and dynamic conditions. Slopes that appear stable under normal conditions may behave very differently after reservoir filling or during earthquake shaking. This makes detailed geological mapping, fault investigation, seismic hazard assessment, reservoir slope modelling and emergency response planning essential.

The project is expected to generate around 300 billion kWh of electricity annually, far more than the Three Gorges Dam. Its scale explains why it has attracted regional attention, including concern in downstream countries over water, sediment and environmental impacts.