Study On The Risk Assessment And Prediction Of Deterioration Of The Bottom Wall Of Xi’an Dayan Pagoda

Brick pagoda is a typical type of ancient Chinese building,and also One of the masonry relics.The Tang and Song Dynasties witnessed the rapid development of ancient Chinese brick pagoda technology and art.Dayan Pagoda is the earliest and largest existing brick pagoda of the Tang Dynasty in China.Wet walls in ancient masonry buildings are common due to rainfall,groundwater and other environmental factors,and usually accompanied by the degradation phenomena such as powdering,shedding,salting out,which threatens the value and safety of ancient buildings.The deterioration of architectural heritage not only appears on the surface of the wall,but mostly implies the instability of the internal heat and humidity.The long-term aggravation of many small diseases may even threaten the stability of the brick pagoda structure.Therefore,it is necessary to study the mechanism of the deterioration of brick pagodas and the impact of the environment on it.It is found that the bottom of Dayan Pagoda has been damp and gloomy for a long time.In recent 40 years,the waterline at the bottom has risen by about 0.5 ～1m,and the wet area on the north wall is even as high as 5m.So this paper mainly focuses on the core issue of "the deterioration of Dayan Pagoda and the cause of the waterline rise".,and discusses the impact of environmental factors on the wall deterioration of Dayan Pagoda.In this research,a field survey and numerical simulation were adopted to clarify the cause of the rising waterline and the source of water of Dayan Pagoda.The correlation between degradation of Dayan pagoda and environmental factors such as temperature,humidity,rainfall and solar radiation was established.Then a coupled heat and moisture transfer model is developed to obtain the heat and moisture distribution in the brick wall and evaluate the impact of rainfall and groundwater.Finally,the trend of waterline rises and deterioration in the future is predicted by simulation.The measured results show that during 2018-2020,the waterline of the west wall of Dayan Pagoda has the largest rise(about 20cm),while the south wall has the smallest rise(about 10cm).The simulation results show that the water source of rising waterline is mainly rainfall rather than groundwater rising.The result contributes to propose environmental control measures to alleviate the degradation of masonry buildings caused by water.Finally,the paper discusses the correlation between the fluctuation of environmental factors and the deterioration of Dayan Pagoda,and predicts the impact of rainfall on the future development of the Dayan Pagoda’s waterline rise and deterioration.And on this basis,the existing protection,monitoring and management strategies of Dayan Pagoda were evaluated.And the protection strategy was discussed and optimized.At present,there are limited studies on the heritage protection of ancient brick pagodas at home and abroad,and few studies on the internal mechanism of the brick pagodas’ deterioration are quantitatively analyzed based on the coupled heat and moisture migration theory.Therefore,the results of this paper will provide new ideas and new directions for the protection strategy of ancient pagodas in China.