Monitoring And Simulation Of Thermal Deterioration Of Unsheltered Earthen Monuments

Thermal deterioration induced by temperature variation is one of the most important degradation modes of unsheltered earthen monuments. Up to now, there is few research about the evolution mechanism of thermal deterioration. For the purpose of conservation of unsheltered earthen monuments, this thesis focused on the thermal deterioration by temperature monitoring and simulation so to reveal the significance of thermal deterioration to unsheltered monuments and to discuss the internal relation between temperature variation and thermal deterioration.Thermal parameter tests were carried out by Hot Disk TPS2500s Thermal Constants Analyzer to measure the thermal parameters (thermal conductivity, thermal diffusivity and volumetric specific heat) of soils, untreated and PS consolidated, from the Ancient City of Jiaohe Ruins. Test results illustrate that the thermal conductivity of soil increase with the increase in water content and dry density, and that decreases after being consolidated by PS:the higher the PS concentration, the lower the thermal conductivity. By data fitting method, good linear relationships were founded between thermal conductivity and thermal diffusivity with water content and PS consolidation.Temperature fields across the sections of artificial walls exposed in the sunlight in Jiaohe site were monitored and simulated through finite element analysis software. Based on the monitoring data and formulas of soil thermal parameters, a differental thermal configuration was established for unsheltered earthen wall, defining material properties hierarchically, such as the original, the deteriorated and PS treated parts of a wall. Through transient thermal analysis, thermal responses of wall sections in different directions during daytime were obtained.The monitored and simulated results contribute to predict the degradation process of unsheltered earthen monuments. In the long run of temperature cycles, deterioration may firstly appear at the top corners and the outside surfaces of the wall, where soil particles become to be looser from the exterior side to the interior side, and finally peel off from the wall surface. This phenomenon tends to be more severe on the west and south wall surfaces. In case that the deteriorated or PS consolidated layer is existed as a cover, the inner part of the wall body presents a better thermal stability, tends to be protected, or not to be deteriorated because of a slower heating up and a smaller temperature variation. In other words, the surface deteriorated layer or PS consolidated layer provides an active protection to the inner wall against further weathering process. However, thermal gradient within deteriorated layer becomes larger that non-deteriorated before. This tends to accelerate the thermal deterioration within the deteriorated layer itself.. Although the PS consolidation improves the mechanical strength of the surface regolith, there exists a weak cohesion boundary below the PS consolidated layer. An elevated thermal gradient in PS consolidated layer increase the risk of peeling off along the PS consolidation boundary.