夯土遗址表层热劣化模拟试验研究

Study on Thermal Deterioration Simulation Test of Superficial Layer on Rammed Earthen Ruins

以武威明长城夯土遗址为例,通过现场调查及室内模拟试验,研究分析夯土遗址表层的热劣化机制.X射线衍射及电镜扫描试验表明:遗址表层与母墙土的矿物成分相似,表层微观结构平滑,但风化明显.热劣化模拟试验表明,试样表层热传导系数、热扩散系数及体积比热均低于母墙.热劣化过程中,表层与母墙的热传导系数与热扩散系数均维持稳定.研究认为,夯土遗址表层与母墙组成具有热性质差异的双层结构,在温差作用下,双层结构间的稳定热差异会使其接触面产生热应力差.热应力差的持续作用使接触面劣化疲劳,导致遗址表层与母墙分离,产生剥离病害.

Field survey,systematic sampling and laboratory tests were conducted to study the thermal deterioration of superficial layer on the rammed earthen ruins,taking the Wuwei Ming Great Wall at Gansu in China as an example.X-ray diffraction and SEM observation indicate that the superficial layer is characterized by obvious weathering and smoother surface when compared with the host soil.Thermal deterioration simulation test shows that the thermal conductivity coefficient,thermal diffusion coefficient and specific heat of volume in the superficial layer are lower than those of the host soil.The conductivity coefficient and thermal diffusion coefficient keep relatively stable during the thermal deterioration simulation process.It is concluded that,under the effect of temperature variation,interface thermal stresses are generated due to the thermal-parameter difference between the superficial layer and host soil,and then the sustaining action of thermal-stress difference results in the fatigue failure and detachment of superficial layer.