The Great Wall of China is one of the largest construction projects ever completed. It was constructed by different dynasties over the past two millennia. The wall measures 6,700 metres in length, which extends from the Jiayuguan Pass in Gansu Province to the Shanhaiguan Pass in Hebei Province. Since the Great Wall trudges through mountain areas, barren deserts of China’s northern interior and vast plains, machinery is impossible to help.
Therefore, the Great Wall was constructed mainly by human labor. It was constructed at that time to act as the first line of defense to protect northern borders of the Chinese Empire against intrusions from nomadic groups. Main Body
Construction techniqueThe early construction process usually starts with clearing and leveling the ground, and then flat stone foundation slabs are placed on the leveled earth. After that, engineers started building the exterior stone walls. The exterior walls are usually paved with three or four layers of regular shaped gigantic rocks. When the exterior walls progress upward, the interior space is filled with different materials, for example earth, clay and rubble, and they are packed into layers to minimize settlement.
However, the above wall-building method may not be perfect as the wall structure may not be stable. In order to make the wall erect, builders improved by using a wall-building technique called hangtu (also called the tamped earth process) The basic technique:
1. Earth and gravel are poured inside removable wooden shutters. 2. Then a layer is tamped down one at a time and this process repeated. With this technique, each layer can be compacted down to 5 inches (originally 7 inches). These walls also stood up especially well in arid areas. When building the Great Wall, workers first completed building the wall sections, and then they tried to combine them into a massive one.
They had used a wall construction technique called rammed earth. It means compacting earth materials between formwork to make a homogeneous mass wall. In other words, rammed earth construction is a process of compressing a damp mixture of earth materials that has similar proportions of sand, gravel, and clay into an external supported frame that molds the shape of a wall section creating a solid wall of earth. After compressing the earth, the wall frame can be immediately removed and it requires an extent of warm dry days after construction to dry and harden. Advantages of the technique:
Using rammed earth technique helps to reduce the reliance on cement in building materials, which is responsible for 5 percent of man-made carbon output. In other words, it helps to cut carbon emissions. Moreover, since rammed earth materials are commonly sourced locally, which means they don’t need to be transported long distances, this further minimizes the environmental impact of them. Materials used: (IF YOU GOT IT, USE IT)
The materials used for different sections of the wall varies greatly and were dependent on availability of building materials near the wall. For example, the section of the wall near Beijing is mostly constructed with quarried limestone blocks while in other locations, the materials may be quarried granite or fired brick. When two different materials are used for two different sections of walls, the finished walls are usually paved with earth and rubble to fill the space in between to form a single unit. Moreover, in desert locations, where there is a scarce of building materials, the wall was built with dirt rammed between rough wood tied together with woven mats. Other considerations
When the engineers built the Great Wall, they had also considered the terrain. On low, flat plains, the Great Wall was built high and more defense lines were added. On the lofty mountains, the wall was built to be a little lower in order to save financial cost. This is because steep cliffs can be served as natural walls to thwart enemies. Moreover, in order to drain precipitation on the wall in a timely fashion, at certain intervals of walls, engineers built barrel drains. With these drains, rain water could be drained to the outside of the wall, which protected the Great Wall from erosion of rainwater. Conclusion
The Great Wall is not just a review of history of over two thousand years, but surely one of the engineering wonders under the collective effortof millions of workers. References:http://www.engineering.com/Library/ArticlesPage/tabid/85/articleType/ArticleView/articleId/80/The-Great-Wall-of-China.aspx http://arch.usc.edu/Programs/Research/RammedEarthConstruction http://www.china-mike.com/china-tourist-attractions/great-wall-china/construction-history/ http://ahmadladhani.wordpress.com/2009/06/08/ancient-building-technique-are-more-eco-friendly/ http://www.travelchinaguide.com/china_great_wall/construction/wall/