The so-called rammed earth plate building is a building built by ramming the loess with a wooden stick (also known as a ramming pestle) to make it dense and hard. Rammed earth houses were built as early as the Yin Shang era. From the point of view of archaeological excavations, the most ancient example of this ramming technology in China is in the place called Baiyingzi in Tangyin County, Henan Province, which is the site of the end of the Neolithic period seven or eight thousand years ago. After the ll century BC (Shang Dynasty), this technology was widely used in various fields, and many large-scale palaces and mausoleums were built with ramming technology, especially the rammed earth platform foundation became a necessary general type of building. In the era of King Yu more than 4,000 years ago, not only used this technology to build the city palace, but also used to build embankments and dams, and control floods. At present, there are still more than 3,000-year-old city palace ruins in Anyang, Zhengzhou, Henan Province, etc., all of which were built using ramming technology. The mall site in Zhengzhou is 6,960m long and is built section by section with a very solid texture. This ramming technique accompanied the migration of the Han people, from the Yellow River basin across the Yangtze River to the south of the Yangtze River, until it spread to the mountainous villages of southwestern Fujian Province, northeastern Guangdong Province, and southern Jiangxi Province.

With the southward migration of the Han nationality, starting from the Tang Dynasty, Fujian, Guangdong, Jiangxi's ramming technology gradually developed, to the Ming Dynasty, the southwest of Fujian mountainous rural houses are built with clay as the main building material, and the use of rammed earth technology to build, this rammed earth technology has reached the peak level, the building is generally three or four floors, up to five or six floors, some of the height of more than 20 meters. The "Construction of the French Style" edited by Li Jie, in the Northern Song Dynasty, stipulates: "The system of building walls, each wall is three feet thick (1 foot 1 0.33 m), it is nine feet high, and its upward slope is halved in thickness; If the height is increased by three feet, the thickness is increased by one foot, and the same is true for the decrease." And now most of Fujian was built in the Ming and Qing dynasties, is the technology crystallization of rammed earth plate construction technology after thousands of years of accumulation and improvement, is the highest achievement of rammed earth civilization in kind, the technical level of this rammed earth wall to the height and width ratio is 25:1 to the peak of the realm, can be said to be a great contribution to the ancient rammed earth technology.

Fujian tulou has pushed the traditional Chinese rammed earth construction technique to its zenith and is now officially inscribed on the World Heritage List. Comparing the rammed earth walls of Fujian Tulou in the Ming and Qing dynasties, we can know the contribution of Tulou people to the development of rammed earth technology.

Take the typical tulou in Nanjing County as an example: the round building Huaiyuan Building, its outer wall is 12.28 meters high, and the bottom wall is 1.3 meters thick; The total height of the outer walls of the square building and your building is 13 meters, and the thickness of the ground floor wall is 1.3 meters; The height-to-thickness ratio reaches 10:1. If the tulou is built according to the provisions of the Song Dynasty's "Construction Law", the thickness of the ground floor wall should be 4.1-4.3 meters. Fujian tulou is nearly 3 meters thinner than the Song Dynasty, not to mention the four or five storey main buildings in some Wufeng buildings in Yongding County, where the thickness of the internal and external walls is only 50 to 60 centimeters. It can be seen that at the end of the Ming Dynasty and the beginning of the Qing Dynasty, Fujian's rammed earth technology has reached its peak.

The ancient craftsmen of Fujian have accumulated valuable experience in the construction of tulou from the aspects of foundation treatment, rammed earth wall materials, wall structure and ramming methods. Because of this, the rammed earth wall of Fujian Tulou can be so thin and can meet the requirements of solidity and earthquake resistance.

The first is the material used for rammed earth walls. The earth wall is made of soil, and the quality of the soil is directly related to the solidity of the earth wall. The area where Fujian tulou is located is mountainous and soil-rich, and the buildings can be built with local materials. Generally, the loess with good viscosity and more sandy content is selected, and if the viscosity is not enough, it should be mixed with "headland mud" (also known as "field bottom mud", that is, the clay that has not been cultivated in the lower layer of paddy field). Generally, the net loess shrinks greatly after drying, and the rammed earth wall is easy to crack, and the sandy content can reduce the shrinkage rate to reduce the cracking of the soil wall, and some of the soil mixed with the old wall (old wall mud) can also reduce the cracking of the soil wall. The purpose of mixing clay is to increase the viscosity and ensure the integrity and sufficient strength of the wall. Since the sand content of the soil varies greatly from place to place, the ratio of loess, clay and old wall mud is completely determined by experience. Usually the raw soil can not be used directly, but the raw soil and the mixed field bottom mud and so on repeatedly hoe, crushed and mixed evenly, and the more carefully the hoe, the longer the stacking time, the better. This actually causes humus to be lost through fermentation (commonly known as "maturation"), and the walls of the soil are strong and not easy to crack.

The rammed earth of the southern Fujian coastal earth building is more particular, usually with the "triple soil", that is, loess, lime, sand mixed and rammed, and some of the soil is also mixed with brown sugar and rice syrup, in order to increase the hardness of the earth wall. Such rammed earth walls are difficult to drive into, and they are still intact after hundreds of years of wind and rain. In addition, the control of the water content in the soil during ramming is also the key to ensure the quality of the soil wall. The water content is too small, the soil is sticky, and the rammed earth wall is loose and obviously not strong; If the water content is too much, the soil wall cannot be tamped, and the wall is easy to shrink and crack after the water evaporates. Usually in the construction, according to the experience mastered, the cooked soil can be compacted into a ball, and the water is considered suitable when it is thrown down.

The second is the structural treatment of the wall. The base of the wall is dry built with pebbles to prevent flooding. The thickness of the wall is gradually thinned from the bottom layer to the top, the outer skin is slightly retracted, and the inner skin is retreated in layers, generally 3 to 5 inches (about 10-17 cm) per layer, which is more stable in structure and reduces the self-weight of the wall. In order to increase the integrity of the wall, the earthen wall is also reinforced, that is, a "wall bone" is set in the horizontal direction. The usual practice is to split the bamboo into long pieces of bamboo more than an inch wide (about 3-4 cm), as bamboo bars sandwiched in the rammed earth wall, and the height of the wall is to put a layer of bamboo bars every three or four inches (about 10-13 cm), and the horizontal spacing is about 6 to 7 inches (about 20-24 cm). There are also small pine branches and small fir branches used as wall bones. The long bamboo tendon knot between the two fangs is called "drag bone" by the Hakka people, that is, it sticks out at the bottom of the template, which is one or two feet (about 33-66 cm) longer than the template. Because the upper and lower fangs are staggered between each layer in the ramming to avoid through joints, the integrity of the wall is greatly enhanced by adding the tie of the wall bone and drag bone.

In the square tulou, the corners of the outer wall should also be reinforced with special reinforcements, that is, the thicker fir or long planks are cross-fixed into an "L" shape (locally called "Pythagorean"), buried in the wall, and a group of "Pythagorean" knots are usually placed on every three "versions" of the earthen wall to enhance the integrity of the corners.

The Hakka people in western Fujian have a set of scientific ramming methods in the construction of rammed earth walls, which is locally known as the "scooping method", and its operation should be completed in three stages: first, it is necessary to separate 2 to 3 inches (about 6.6-10 cm) in two directions along the thickness and length of the wall, and each hole should be licked twice, and the Hakka people are called "heavy pestle"; Then between every four holes, the Hakka people call it "layer pestle", and finally lick the rest of the place, the purpose of "heavy pestle" is to fix the clay, in order to ensure that the pestle is compact, if irregularly scooping, the clay is squeezed around, the thickness of such a large earthen wall is difficult to ram evenly, rammed solid. After tamping, it is necessary to insert the pointed steel brazing into the earth wall, and the compactness of the earth wall ramming is usually judged by the depth of the steel brazing insertion by experience, and this strict detection method is also an important link to ensure the quality of the earth wall.

In addition, the ramming of the earthen walls of Fujian tulou was carried out in a phased and orderly manner. The height of each floor of the earth building is about 3.6 meters, which is usually rammed in two stages: the first stage is rammed eight plates, each version is 40 centimeters high, and then stopped for one or two months, the second stage is to wait for the wall to dry to a certain extent, and then the ninth version is rammed, and then the groove of the floor keel is dug on the earth wall, and the depth of the groove varies with the size of the keel to ensure the level of the floor. After laying the keel, the above two stages of ramming can be repeated without waiting for the wall to dry, ramming the eighth version of the second floor, and so on until the top floor. In this way, the phased ramming is not only convenient for digging grooves, so that the wall has sufficient strength when the floor keel is shelved, but also can cooperate with the farmer's farming season to construct the new void in stages.

This is a rammed earth wall used to build a building, and the rammed earth wall in the tomb is made in a similar way to this, and it is more solid, so it is no wonder that Duan Yufeng chose to blow up the tomb.