What's the use of building walls in earthen pits and kilns on the Loess Plateau?

In the plane area where there are no cliffs, hutongs and other areas that are conducive to the construction of the first two kinds of caves, people use old abandoned waterlogged ponds, natural potholes and places that they think are good in geomantic omen and convenient in and out. In fact, Kengyuan is the most direct development and evolution of ancient "cave dwelling" houses in Qingyang after the people of the Loess Plateau entered the civilized era. This kind of residence is generally based on an old waterlogged pool or abandoned pit, with a big pit and a cave carved in the wall. Most caves are dug on three sides, and one side is open to traffic. The biggest problem in this pit life is inconvenient drainage. People have to dig a round pit in the middle of the yard to store the rainwater in the yard. There are many low walls on the cliff. This kind of Zhuangzi, built for the people in the original place of residence, is time-consuming and laborious, and is prone to floods. Except that Zhuang Ming, which was built halfway up the mountain, is somewhat special, the basic shape of the cave courtyard is basically the same. The appearance of the cave is a conical circle. Due to the different soil quality, different convenient procedures of natural conditions, labor force, construction time and other factors, the situation of building cave manor in the same area is often different. Mainly manifested in the size of the yard, the height of the kiln surface, the number and depth of caves and so on. Generally, the length of pit cave is about15m, and the depth is about 6m. Due to the nature, topography and landform of the site, the width varies greatly. Small ones are generally more than ten meters square, often facing north and south. Generally, there are three caves in the front, and the same number or less caves are built on the left and right sides, which pays great attention to left and right symmetry. Access channels are mostly built opposite the main kiln of the champion. Generally, caves are not built on the side where the passage is located, which is only smaller than many auxiliary caves on the three sides of the front, such as toilets, chickens, pigs, cows and sheepfold houses. The main kiln (that is, the front cave) is generally slightly larger than other caves, about 6.6 meters deep, 3-4 meters high and 3-3.3 meters wide at the bottom. The larger yard is more than 20 meters or even dozens of meters square. A kiln can accommodate dozens of large families by digging five or seven holes. The hole is made of adobe or stone, leaving a door, two windows or three windows. Set up a heatable adobe sleeping platform near the window in the kiln, and then put simple furniture in turn. A cave used as a kitchen is also used to build a kang, a pot table, a chopping board, pots and pans by the window. The chimney of the pot platform must pass through the heatable adobe sleeping platform or cliff top outside the kiln, which is probably the remarkable feature that distinguishes Qingyang cave from other dwellings!