【作者】 沈云霞；

【导师】 谌文武；

【作者基本信息】 兰州大学 ， 岩土工程， 2011， 硕士

【摘要】 在西北干旱和半干旱地区独特气候条件下遗存了大量珍贵的土遗址,如长城、故城等。这些宝贵的文化遗产不仅是智慧的结晶,也是政治、军事、科学、文化、经济和社会发展进程的历史见证,具有极其重要的意义。土遗址长期处在极端恶劣的气候环境之中,导致土体发育各种病害,其根本原因是土体劣化致使抵抗外界破坏能力下降所致。集中降雨和强烈蒸发的气候改变不但加剧了区域内的干湿循环,还加剧土的盐渍化,盐渍劣化成为西北地区土遗址中典型的工程地质问题之一。因此,加强干湿循环作用下盐分对遗址土的影响研究为预防这些建筑文物发生更大的变形破坏具有科学的指导性,同时也可为文物保护工作提供有效的具有针对性的理论依据。在对西北地区遗址土盐渍劣化定性认识的前提下,选择合理的盐分含量、类别开展干湿循环作用下的含盐遗址土盐渍劣化试验。通过对不同盐分类别、不同盐分含量的试块,在三次干湿循环后所进行的直接剪切试验、无侧限抗压试验以及抗拉试验,较为直观的认识不同盐分类别、盐分含量对含盐遗址土的盐渍劣化程度；通过声波试验,测试在干湿循环过程中含盐遗址土的结构变化,从宏观的角度表现遗址土盐渍劣化过程；通过微结构观测揭示含盐遗址土力学特性与其微结构各参数之间的内在联系,建立具有微结构变化特征背景的关系式,从微观层面研究干湿循环对遗址土盐渍劣化。主要研究成果为：(1)盐渍劣化后的遗址土力学性能测试表明：随着含盐量的增多,试样的黏聚力、抗压以及抗拉强度逐渐减小,内摩擦角则呈现先增大后减小的变化规律；掺入Na2SO4盐分的试样劣化程度更为严重,其表现出的力学性能也相应的比掺入NaCl盐分的试样有所降低；掺入复合盐(Na2SO4+NaCl)的试样,因为NaCl盐分的存在,致使Na2SO4的溶解度明显降低而提前析出,不具有表聚性,对试样整体破坏性最大,表面强度则介于掺入单盐的试样之间。(2)声波测试结果表明：经过三次干湿循环后的纵波波速相比第一次干湿循环后的纵波波速减小了10%以上,且随着含盐量的增加,波速减小幅度逐渐增大,从侧面证实了干湿循环作用下的含盐遗址土确实存在盐渍劣化的过程；经过回归分析发现,试样纵波波速与抗压、抗拉强度之间存在良好的幂指数关系,与抗剪强度之间的关系则表现较强的离散性。(3)通过微观结构观测,孔隙中确实存在针状的Na2SO4晶体以及颗粒状的NaCl晶体；随着含盐量的增加,微观结构类型由骨架状向基质状过渡,土颗粒表面的亮点增多,颗粒粒径趋于均一化,整体结构较为松散；利用多元逐步回归分析方法,分析盐渍劣化后遗址土力学强度参数与微结构参数之间的相关性,得出具有一定参考价值的回归方程和模型。更多还原

【Abstract】 A large amount of precious relics of ancient earthen architecture sites have been saved under arid and semi-arid climatic conditions in Northwest, such as the Great Wall and the Jiaohe Ruins. These precious cultural heritages which are of extremely important, not only representative the achievement of wisdom, but also the historical evidence of the development process in political, military, scientific, cultural and economic. The reduction of the capacity to resist external damage is the root cause of the development of various diseases in soil site, which at the long-term adverse climate change in extreme environment. Evaporation of rainfall and a strong focus on climate change increased the wet and day cycles and salinization of soil, the latter becomes the typical engineering problems of soil sites in Northwest. Above all, concentrating on the research of wet and dry cycles of soil salinity on the soil site to prevent more damage to the heritage has a great significance, what’ more, the research can provide effective theoretical basis on the protection of cultural relic.Choosing a reasonable salt content, the purpose is to do research on salt saline soil degradation test site by wet and day cycles under a premise of qualitative understanding to the soil salinity of sites in Northwest region. First, we may have a more intuitive understanding of influence about different types and contents of salt on soil saline by direct shear test, unconfined compression test and tensile test on various salt types and contents test blocks after three wet and dry cycles; Second, the process of soil salinization deterioration may display from a macro point by doing acoustic experiment to test changes in the structure of soil sites contained with salts under wet and dry cycles; Third, we could establish relationship with micro-structure changes and carry out intensive study on effect of wet and dry cycles on the site of degradation of soil salinization in micro point by reveal the mechanical properties of soil salinity sites and the intrinsic link between the micro-structure of the various parameters.The follows are positive results:1. The mechanics performance testing of the test sample after salinized deterioration shows:With the increase of salt content, the cohesion of the sample, compressive and tensile strength decreases, the internal friction angle of the show is decreases after increase; The sample mixed with Na2SO4 salt deterioration far more serious, compared to the sample adding NaCl salt, its mechanical properties is reduced; Because the existence of NaCl salt, causing the solubility of Na2SO4 reduced significantly, and crystallized early, make the surface strength of the samples mixed with complex salts between incorporation of a single salt while the strength of entire sample is the lowest.2. Acoustic test results show that:Compared with one Dry-Wet cycle, the longitudinal wave of samples decreased by 10% after three cycles, and reduction is increased gradually with the increase of the salt content, from the side confirmed to the salinized deterioration of the ancient relics soil by dry-wet cycle; After regression analysis found that power exponent relationship between longitudinal wave and compressive, tensile strength, the relationship between the longitudinal wave and shear strength is discreteness.3. By microstructure observation, granular Na2SO4 and needle like NaCl are exist in the pores. The type of microstructure change from the matrix to the skeleton-like as the increase of salt content, what is more, the highlight of the surface of soil particles increased and the particle size tends to homogenization, whereas the overall structure is loose. Using multiple regression analysis, we will get certain reference value obtained regression equations and models after analysis of soil salinity deterioration of mechanics strength and the correlation between parameters.更多还原