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
The 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...