Deliberately making a road icy sounds like a bad idea for disaster, but in 16th-century China it helped things run smoothly. Repairs to the Forbidden City in Beijing in 1557 called for huge stones from a quarry(采石场) more than 70km away. The biggest was the 300-ton“Large Stone Carving”.Such stones were too heavy for any cart, and too fragile for rollers. The builders adopted a wise alternative approach to carry the heavy stone.
They dug a series of wells, spaced a few hundred metres apart, along the route to the quarry. Then, in the depth of winter, when temperatures reached around -4℃, buckets of water were poured on to the dirt track, transforming it into an ice road.
The stone blocks were pushed along the road on wooden sledges. Modern engineers have calculated that it would take 1,500 workers to drag a sledge on the dirt road, but only 300 on ice. Ancient texts suggested the ice was made slippery with more water; and this reduced the friction further and just 50 men could pull a sledge. This technique only works when the temperature is close to zero, otherwise the film of water freezes too quickly.
The researchers at Princeton University estimated that the blocks could be moved at six metres a minute, and the journey could be completed in 28 days. This would be well before the spring when the ice would melt. It was once suggested that similar ice-sledges transported Stonehenge stones, but the ground that had a lot of holes and comparatively mild conditions probably rule this out.
本时文内容由奇速英语国际教育研究院原创编写,未经书面授权,禁止复制和任何商业用途,版权所有,侵权必究!(投稿及合作联系:028-84400718 QQ:757722345)