Study on the Characteristics and Influencing Factors of Erosion Diseases on the Upper Part of the Ming Great Wall in Gansu Province, China

Most of the past studies only focus on the bottom erosion but ignore the upper erosion. Therefore, this paper reveals the morphological characteristics and distribution rules of upper erosion and constructs a simple framework of its influencing factors by field investigation and data analysis of the Ming Great Wall in Gansu Province. The results show that the upper erosion occurs only on the rammed earth walls, which can be morphologically divided into slender groove type and discontinuous cavity type. Except for Shandan County, the linear erosion rate, average erosion depth and average distance to the top of the upper erosion gradually increased along the Ming Great Wall in Gansu Province from northwest to southeast, while the average erosion height gradually decreased. Climatic factors have an important influence on the severity and location of upper erosion, of which rainfall is the most critical factor, followed by daily temperature difference and solar radiation. The soil property factors that play a role are those related to water and salt in the soil, which only have some influence on the severity but not on the location. It is tentatively inferred that the formation of upper erosion may be related to the destruction of water and salt changes within the soil caused by environmental changes.