The Study Of Rainfall Erosion Models And Mechanism About The Great Wall Of Ming Dynasty In Yuyang Region

The Great Wall is one of the World Cultural Heritage, and the Great Wall of Ming dynasty is the most complete one in China. Being affected by the human and nature factors, the situation of Great Wall is pressing, and the conservation is extremely urgent. The preventive conservation means that to take effective measures before damage occurring in order to avoid or relic the destruction. The damage mechanism is an important component of preventive conservation, and is the premise of making protection measures. The rainfall erosion models and mechanism research of the Great Wall in Yuyang has great significance for evaluating the existing condition in the similar circumstance and for establishing certain conservation planning. The research focus on the developing process of rainfall erosion of hammed earthen site, to exploring the mechanism that how the rainfall characteristics and soil properties result in the deterioration of hammed earthen site, ultimately, draw the conclusion of rainfall erosion mechanism of The Ming Great Wall under the typical rainfall condition in Yuyang region.By field investigation and statistic analysis result, we draw the conclusion about the existing forms and rainfall erosion models. Statistic analysis result helps find the four typical combinations of rainfall intensity and rainfall duration, which offer the aging condition in field experiment that test the damaging process of hammed wall. The laboratory test verify the function that soil water content for rainfall erosion models and soil strength for rainfall erosion degree. And finite element numerical simulate calculation was taken to calculate the stable coefficient of five typical site forms under four typical rainfall conditionThe research shows that:There are dry-wet erosion, scouring erosion and collapse erosion three damage models in the rainfall erosion process of Ming Great Wall in Yuyang region, and the three models degree are increasing. In Yuyang region, almost 80% rainfall are light rain which rainfall intensity below 0.1mm/min and rainfall date below 10mm, and the rainfall erosion models under this condition is dry-wet erosion, which is the most frequent erosion models in the whole year. Under heavy rain or rainstorm condition which occurs accidental in summer and autumn, the erosion models of the Great Wall is scouring erosion and collapse erosion, in general case, the heavy rain and rainstorm are keep 2.5hours to 3.5hours and the rainfall intensity are above 0.3mm/min. The scouring erosion and collapse erosion are the most destructive erosion models although they happened at a low frequency. Under the heavy rain and rainstorm, the high soil water content is more easily leads to collapse erosion, and there are quantitative relationship between soil water content and soil saturated time, water content and collapse time, water content and soil loss mass. The hammed soil strength has effect on the erosion models and soil loss mass. At the early stage of heavy rain or rainstorm, the fragile hammed soil performs wet function until saturated, and at the late stage it performs collapse as whole. And the strength hammed soil performs sustained scouring erosion at a low speed, and the hammed soil density and soil loss mass exist quantitative relationship. The stability of hammed soil determined by site shape and rainfall intensity, the hammed earthen site with steep facade and lots cracks are more easily collapse under high rainfall intensive.