遗址土劣化进程中微观结构变化的类比研究

长期的风化会使遗址土体劣化，进而威胁到遗址本体的安全，但在自然条件下这一演化过程尚不明确。遗址土体微观结构的变化是该过程的重要体现，研究选取风化条件近似而暴露时间不同的黄土质边坡作为类比对象，采用扫描电镜法（SEM）和压汞法（MIP）分别对表部以及内部土样的微观孔隙结构进行观察和量测。试验结果表明，表部土体微观结构的变化程度大于内部土体，并呈现一定的规律性；与内部土体相比，表部土体的土颗粒排列为致密的叠片状；其孔径分布为双峰模式，团聚体内孔隙占比较大；随着风化时间的增长，表部土体的孔隙总体积和表面分形维数逐渐减小，导致孔壁粗糙程度降低，减小了颗粒间的摩擦，在宏观上容易诱发土体表层的剥离损耗或其他病害。

Analogy study on evolution of microstructure of earthen monument during natural weathering process

The long-time weathering causes significant deterioration of earthen building materials, which poses a great threat to the durability of earthen monuments. This process, however, keeps unknown under the real weathering conditions because of their complexity and large time scale. Soil micro-structure changes with the natural exposure and its evolution is an important feature characterizing the deterioration process. The loess road cuts, which were exposed to similar weathering for different years, were selected as analogy model to capture the evolution of micro-structures of undisturbed soil samples from surface and internal parts, respectively. Scanning electronic microscope (SEM) was used to observe the fabric and texture of soil samples. Mercury intrusion porosimetry (MIP) was used to measure the pore size distribution (PSD) quantitatively. The experimental results show that the micro-structure of surface soil changes much more significantly with weathering time compared to that of internal soil. The fabric of surface soil is in lamellar form and its PSDs are bimodal (i.e., inter-aggregate pores and intra-aggregate pores). The inter-aggregate pores volume accounts for a larger proportion in the surface soil and shows a decreasing trend with weathering time. Fractal analysis of pore surface indicates that building age has a tendency to decrease the irregularity and roughness of micro-pore walls in the surface soil samples, which could lead to a reduction in friction forces between soil aggregates or particles. Consequently, surface weathering, like crusts or peeling off, or other diseases would be engaged at the macro-scale.