兰州大学机构库 >土木工程与力学学院
干旱区夯土遗址表层热劣化剥离研究
Alternative TitleStudy of Thermal Deterioration and Detachment of Superficial Layer on Rammed Earthen Ruins in Arid Area
杨龙
Thesis Advisor张虎元
2018-06-01
Degree Grantor兰州大学
Place of Conferral兰州
Degree Name硕士
Keyword土遗址 表层 风化 热物理参数 热应力 模型
Abstract

我国西北干旱区集中而高强度的降雨在冲刷夯土遗址表面时,也致使其表面产生结皮表层。在露天环境中,结皮表层的劣化剥离是夯土遗址存在的主要病害。其中,由于区域内剧烈的昼夜温差及季节温差,遗址表层与母墙的温度场及热应力场将发生剧烈变化。温度场及热应力场的剧烈变化加剧了夯土遗址表层的劣化剥离过程,这种由于温度变化导致的遗址体表层劣化剥离被称为热劣化剥离。

以甘肃省武威市凉州区明代夯土长城遗址为例,通过现场调查取样及室内试验相结合,综合研究干旱区夯土遗址表层的热劣化剥离过程。现场调查表明遗址体保存较为完整,遗址体的表层劣化剥离病害广泛发育。现场取原状样于室内通过XRD粉晶衍射试验、电镜扫描试验及粒度分析试验综合研究遗址结皮表层与内部母墙土体之间存在的矿物成分差异、微观结构差异及颗粒粒度分布差异。结果表明:(1)母墙与表层土体的矿物组成大致相同,主要矿物为石英、长石及云母类矿物,其体积含量超过总矿物组成的75%。(2)遗址表层中的土颗粒呈薄片状,并按叠瓦状紧密排列;母墙土颗粒表面粗糙,形状呈角砾状,颗粒无序紧密排列,夯筑痕迹明显。(3)母墙土颗粒的体积分布曲线呈双峰状,表层土的体积分布曲线呈单峰状;母墙土体中砂粒组土颗粒含量高于表层土,粉粒组土颗粒含量低于表层土。对现场所取的原状样于试验室重塑并进行降雨模拟试验,让试样生成结皮表层,再进行热劣化模拟试验,并在热劣化模拟试验过程中监测试样表层的热物理参数变化规律。试验结果表明:(1)试样表层结皮形成后,表层的热传导系数降低,热扩散系数降低,降低体积比热。(2)在加速热劣化模拟试验及自然模拟试验的过程中,试样表层的热传导系数、热扩散系数及体积比热均维持稳定。试验证明遗址体表层与内部存在显著热物理性质差异,而且这种差异在热劣化剥离过程中维持相对稳定。基于此,研究认为:干旱区的夯土遗址的表层与母墙类似于双层结构,在温差循环作用下表层与内部将产生显著的温度场差异及热应力场差异,这将导致夯土遗址体表层与内部土体间的疏松带疲劳劣化,最终导致夯土遗址表层劣化剥离。

基于夯土遗址表层与内部土体存在稳定且显著的性热物理性质差异这一特性,建立两种夯土遗址表层热劣化剥离的半定量分析模型:单介质裂纹扩展模型和双介质接触面疲劳劣化模型,尝试通过半定量的方法研究探讨干旱区夯土遗址表层的热劣化剥离过程。

Other Abstract

The centralized and heavy  rainfall not only erode the superficial layer of the rammed earthen sites, but also lead to the formation of surface crust on rammed earthen sites in the northwest arid region of China. As is known to all, the detachment of superficial layer is a important deterioration on the earthen sites. Dramatic changes of daily and seasonal temperature differences in large sites will result in significant changes of thermal field and thermal stress field in sites. Furthermore, The significant changes of thermal field and thermal stress field will intensify the process of superficial layer’s deterioration and detachment on the rammed earthen sites. It is the thermal deterioration and detachment process of superficial layer on rammed earthen that mentioned above

Field survey, systematic sampling and laboratory tests are conducted to study the thermal deterioration and detachment process in superficial layer on rammed earthen sites taking the Wuwei Ming Great Wall, Gansu, China for example. The field survey find that the sites is kept intact and the superficial layer deterioration is developed widely. laboratory X-ray diffraction, SEM observation and laser particle size analysis are used to research the mineral composition difference, microstructure difference and the particle composition difference between superficial layer and host soil. X-ray diffraction result shows that the mineral composition difference between superficial layer and host soil is very little, and the content of quartz, micas and feldspar exceeds75%. SEM observation shows that the particles in superficial layer are shown as lamelliform and imbricate arrangement, but rough elliptical shape, unordered close arrangement and obvious rammed vestige are shown in host soil. Laser particle size analysis result that host soil is marked by higher sand and lower silt and superficial layer soil is marked by higher silt and lower sand. In addition, the volume distribution curve of superficial layer is single peak and host soil is double peak.

Based on the simulated rainfall test on remolded specimens, the superficial crust is formed. Then the thermal deterioration accelerated simulation test was taken to research the variation of superficial layer’s thermophysical properties of specimens. The results show that the superficial layer’s thermal conductivity coefficient, thermal diffusion coefficient and specific heat of volume are lower after the superficial crust formed. And superficial layer’s conductivity coefficient, the thermal diffusion coefficient and specific heat of volume keep relatively stable during the thermal deterioration accelerated simulation process. The test proved that there are obvious thermophysical properties differences between superficial layer and the host soil. meanwhile, The obvious differences keep stable during the thermal deterioration and detachment process. Therefore, rammed earthen sites are similar to double layer structure, and obvious thermal field difference and thermal stress field difference between the superficial layer and the host soil will be generated under the cyclic action of temperature. The differences will lead to fatigue deterioration of contact zone which between the superficial layer and host soil. Furthermore, it will lead to the detachment of superficial layer.

Based on the property that there are obvious differences between superficial layer and host soil in rammed earthen sites. In order to semi-quantitative research the superficial layer’s deterioration and detachment of rammed sites in arid region, some necessary assumption are used to build two models which are named homogeneous medium crack propagation model and two-layered medium interface fatigue deterioration model.

URL查看原文
Language中文
Document Type学位论文
Identifierhttps://ir.lzu.edu.cn/handle/262010/226464
Collection土木工程与力学学院
Recommended Citation
GB/T 7714
杨龙. 干旱区夯土遗址表层热劣化剥离研究[D]. 兰州. 兰州大学,2018.
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