Where earthquake risk is ever-present, there is a window of opportunity to prevent disaster. We often meet local champions who take this to heart. One of them is a colleague in Bhutan, a small nation in the towering Himalaya. Huge earthquakes have occurred on a major fault that runs along its southern border with India, but not for a while, which leads scientists to expect a big one.
Dago Zangmo is a well-educated Bhutanese engineer with a master’s degree in structural engineering from Japan. She takes part in a core group of engineers that GHI’s international experts are mentoring to become Bhutan’s earthquake engineering leaders. The team is learning how Bhutan’s unique building types behave during shaking and how to make them safer. Dago took on a personal project too, and we all learned from it.
Dago’s parents lived in the traditional rammed earth home above. After a moderate 2011 earthquake, it suffered large cracks, and walls moved when someone walked to the third floor. Traditional style buildings are Bhutan’s cultural treasures, and Dago’s mother insists on doing things the traditional way. Given the damage to the house though, she let Dago design a new home in the traditional style. Dago’s master’s degree dissertation was on rammed earth, and she used her knowledge of vernacular structures to design a safer single-story rammed earth home. You can see the beginning of the new walls in front.
Rammed earth is the main traditional construction practice in western Bhutan, characterized by massive rammed earth walls with wooden floors and roofs. The foundation is stone masonry with mud mortar. Rammed earth is inherently weak under side-to-side earthquake motion, so buildings must be carefully built in order to reduce the risk. People developed good practices over the centuries to increase the strength and stability of these buildings and to suit local conditions. However, the practices were not sustained, and rammed earth structures have become more vulnerable to earthquakes. GHI’s challenge, shared with our Bhutan partners, is to make them earthquake resistant while maintaining historic features.
Rammed earth walls are constructed with a minimum thickness of 2 feet, and tall walls must be even thicker. Soil is poured into wooden forms (shown above) and rammed with a wooden tool that has with one end shaped like an elephant leg. Normally, it takes half a day to complete one block of rammed earth wall. Women usually do this task, and they sing while they work--nothing to improve on that! Dago ensured that her family’s new home followed the traditional good construction practices. For this talented engineer, safe construction is both a personal and a professional pursuit. Millions of people face manageable risks in vulnerable communities. It matters to us that each person has a story, dreams, and a family.