宁夏干旱区石质文物劣化机理及岩石材料耐久性研究

In view of endangered prominent problems results from serious weathering of open-air stone relics in arid region of Ningxia, the degradation mechanism and durability of the rock will be studied in this project. Firs, the weathering degree, characteristics of fracture development and rock strength attenuation law are obtained by the field tests with the geophysical prospecting and close range photogrammetry. Then, the indoor simulation accelerated aging analysis and evaluation are carried out with freezing and thawing test, wind tunnel experiment and ultraviolet radiation together with NMR,SEM and XRD. The damage process is displayed dynamically with the analysis of pore development , extension features and strength. The decay function model will be proposed with the index of decay constant and half-life period. At the same time, the thermal-mechanics(TM) coupling is to be build based on equivalent continuum theory.And the ASHRAE intensity of solar radiation in clear sky model is used to analyze the stress distribution of rock thermal, which will descript the typical Ningxia arid environment factors of rock material thermal degradation mechanism quantitatively. Finally, the damage is introduced to the TM coupling after the porosity is defined as the damage factor. The Laws for the degradation and durability under the several environmental factors coupling will be simulated numerically. The damage of rock mass stress distribution and structural strength are analyzed. The critical values will be constructed for the security porosity and environmental condition. The research results will clarify the stone relics deterioration process and speed, which are the foundation of rock material deterioration warning criterion, and meanwhile they will provide important theoretical guidance for the future design of the protection and restoration.

针对宁夏干旱区环境致石质文物风化严重而濒危的突出问题，通过现场物探和近景摄影测量方法，获得文物风化等级、裂隙发育特征和岩石强度衰减规律。模拟温度、风场和光照等主要环境因子，开展室内冻融、风洞、紫外辐射等老化试验，结合核磁共振、微观测试和力学等试验，探讨岩石物理、力学、(矿物)成分及微观结构特性，重点动态显示其损伤过程，分析孔隙发育、扩展特性和抗拉强度变化规律，引入衰变常数和半衰期的概念，提出岩石衰变函数模型。理论上基于岩石等效连续介质模型，利用ASHRAE太阳辐射强度晴空理论，将孔隙率作为损伤因子建立热-力-损多场耦合场，分析岩石热劣化特性、岩体损伤应力分布和结构强度，提出文物安全稳定性和环境条件的临界数值。研究成果旨在揭示长期服役于文物的岩石材料劣化特性和耐久性机理。为提高适于宁夏区情露天不可移动文物预防性保护和修复能力提供科学理论依据。

我国宁夏境内的贺兰山岩画是中国北方游牧民族的重要文化载体，在世界岩画中占有极其重要的地位。但是，经过长期的风化侵蚀，濒临消失。为此，本项目采用室内试验和理论建模相结合、多学科交叉、多尺度跨越及引入声发射技术，首先，测定贺兰山岩画载体材料岩性，开展物理特性试验，探讨块体密度和颗粒密度关系及吸水率随时间变化规律，利用风洞试验探讨风蚀模数变化，采用超声波测量波速，开展力学变形破坏特性试验研究。然后，干湿循环-化学-力学多场耦合，研究两种溶液下砂岩变形破坏和力学性能规律，观察微观结构演化历程，进行侵蚀过程化学热力学分析。最后，基于声发射原理，结合力学试验 分析岩石变形破坏模式，探究声发射信号特征，讨论AE时空演化规律，建立基于声发射累计振铃计数的损伤演化模型。研究结果表明，贺兰山岩石属于弱变质层状钙质细粒石英砂岩，主要碎屑为石英及少量长石，碎屑间胶结物为碳酸盐和少量泥质。砂岩强度与循环次数之间的指数函数模型，干湿循环交替导致强度和弹性模量均显著降低并逐渐趋于一个定值，破坏特征则由张拉劈裂—剪切转变，受到了不可逆的渐进损伤作用。微观结构表现出由一致的致密状→疏松状→泥化过渡、颗粒主要呈现出扁平→卷曲→紊流推进、孔隙之间由紧密→连通→扩张演化。AE时空演化规律能够定量表征岩石内部损伤过程，可以用来判断岩样岩石内部（微）缺陷状态；利用岩石声发射现象急剧增加阶段的起点判断岩石的破坏前兆。根据这一特征可以预测文物安全稳定性临界值和岩（体）石的失稳时间。岩石损伤发展主要经历微损伤、损伤产生、损伤加速扩展、损伤稳定扩展四个演化历程；损伤演化模型的力学和物理意义明确，可以描述贺兰山岩石损伤破坏过程和状态。发展了一种宁夏干旱区环境致石质文物劣化的分析方法，丰富了水岩相互作用的内涵，突破宁夏贺兰山岩画载体材料劣化问题的定性解释和共性评价，实现对长期服役文物的岩石材料劣化性机理的理论研究和定量描述。