Expert Risk Articles
Risk Consulting In Focus: How To Survive Earthquakes In Mud Buildings
AGCS risk experts journey to the mountains of Fujian province in China to learn about tulou, ancient structures which were effective against natural disasters – and enemy attack, as Senior Risk Consultant, Ryan Du explains.
Designated by UNESCO as a World Heritage site in 2008, the 46 Fujian tulou (literally, “earthen buildings”) sites, were mostly built in the 12th Century by the Hakka people of Southern China. Wracked by years of wars, many migrated to Fujian in order to escape fighting. They settled on wetlands due to lack of arable land and despite the ground being less than desirable for construction.
As today, the Hakka had to consider a wide variety of risks when building their homes. Flooding was common. The unstable and wet ground on which the tulous’ foundations were built was low-lying and prone to collecting water. In addition, the region was exposed to natural catastrophes like earthquakes and windstorms. The mass migration of the Hakkas was also met with hostility by the natives and skirmishes often broke out.
Without cement and other modern construction methods and materials, the Hakka improvised to ensure the tulou would withstand destructive natural disasters. Despite their name, tulou construction materials consisted of more than just mud, incorporating pine logs and stones, with walls made of mud reinforced with bamboo, sand, and lime compacted with a thick staff. This soft foundation proved to be effective during earthquakes, bracing the structure and preventing it from toppling or collapsing. While early tulou were rectangular and single-storied, as the Hakka population grew buildings increased in height, with some growing to more than 16m tall. They discovered that multistoried, rectangular tulou sustained more windstorm damage due to the wall faces bearing the full brunt of the wind. In response, circular tulou were built, lessening the wind-resistance and significantly mitigating storm damage.
In addition to providing shelter, tulou also were equipped for defense against various methods of assault. One solution was to thicken lower walls by a meter or two in order to mitigate attempts to break through with fire or conventional weapons. The walls of some tulou actually stopped cannon fire. Another safety innovation was to limit the number of openings on the first or second levels of multistoried tulou, making it difficult for enemies to enter. Further exposure was minimized by extending wall bases two meters underground to dissuade intruders from digging inside.
Another peril for tulou, owing to the amount of wood and bamboo used in fortifying them, not to mention enemies’ tendency to employ it, was fire – still the bane of building managers everywhere today. While there were no sprinklers or fire hydrants, tulou used an ingenious sprinkler-like method to deliver water to the premises. In addition to easily accessible wells, water tanks were installed at the top of exterior walls over the gate, which could quickly extinguish fire before it grew out of control.
That tulou have survived, considering the Hakka people did not have the sophisticated risk mitigation techniques we have today, is a credit to their design, which aids in minimizing risk exposure. Risk managers and engineers should bear this in mind, as proper design in accordance with proven standards will help avoid the need for expensive retrofitting or repairs, should an accident occur in future.