大足石刻砂岩材料风化程度量化评估

发布时间：2018-09-11 13:03

【摘要】：大足石刻位于重庆市大足区境内,是唐末、宋初时期的宗教摩崖石刻,以佛教题材为主,儒教和道教造像并陈。石刻文物经历了数百年乃至千余年的历史时期,发育了不同类型和不同程度的风化病害。然而,对于砂岩质石窟寺及石刻保护的核心问题,表层岩石的风化破坏还缺乏明确、清晰的定性、定量认识和评估。论文以大足石刻砂岩材料为研究对象,选取不同风化程度砂岩样品48个,测试样品的里氏硬度、对测波速、平测波速、抗压强度、钻进阻力、毛细吸水系数、矿物成分、化学成分、微观结构、干密度、孔隙率等指标。分析各测试结果与风化程度的相关性,对比各检测技术手段的优缺点,综合多种测试技术进行成果解释。全面掌握大足石刻砂岩材料风化过程中在物理力学性质、矿物化学成分、微观结构方面的变化规律,建立大足石刻砂岩材料风化程度量化评估体系。本文研究的主要结论如下:(1)大足石刻砂岩材料的干密度较小,孔隙率和吸水率较大。并且开孔孔隙率与总孔隙率相差不大,与之对应的是自由吸水率和饱和吸水率相差不大(即饱水系数较大)。这些特性导致砂岩容易受水及水中盐分的影响,抗风化能力稍弱。(2)通过测试新鲜岩芯的抗压强度,并参考《工程地质手册》第四版中关于风化程度的定量划分标准,以及各指标之间的拟合关系,得到大足石刻砂岩材料的风化程度量化评估体系。但每种测试指标各有优缺点,运用多种指标对研究对象进行综合评价,可以有效避免单个指标的局限性。(3)大足石刻砂岩材料风化过程中伴随着矿物成分和化学成分的变化,具体表现为方解石和白云石的分解,以及Na、Mg、Ga、K的氧化物流失减少。所选矿物风化指数Wck、以及4种化学风化指数均对大足石刻砂岩材料风化程度具有较好的指示作用。大足石刻砂岩材料中含有一定量的的黏土矿物(主要是伊利石、伊蒙混层矿物、绿泥石、绿蒙混层矿物),这些黏土矿物具有吸水膨胀、失水收缩的特性,容易导致砂岩风化。
[Abstract]:Dazu stone carvings, located in Dazu district of Chongqing, are religious cliff stone carvings in the late Tang Dynasty and the early Song Dynasty, with Buddhism as the main theme, Confucianism and Taoism as statues and Chen. Stone carvings have experienced hundreds or even thousands of years of history, developed different types and different degrees of weathering disease. However, there is a lack of clear, qualitative, quantitative understanding and evaluation of the weathering damage of the surface rock for the core problems of the protection of sandstone grottoes and stone carvings. Taking Dazu stone engraved sandstone as the research object, 48 sandstone samples with different weathering degrees were selected to test the Richter hardness of the samples, and the wave velocity, compressive strength, drilling resistance, capillary water absorption coefficient and mineral composition of the samples were measured. Chemical composition, microstructure, dry density, porosity and so on. This paper analyzes the correlation between test results and weathering degree, compares the advantages and disadvantages of each testing technique, and synthesizes various test techniques to explain the results. A quantitative evaluation system for the weathering degree of Dazu stone engraved sandstone materials is established by mastering the changing laws of physical and mechanical properties, mineral and chemical composition and microstructure of the sandstone materials in Dazu lithography. The main conclusions of this paper are as follows: (1) the dry density, porosity and water absorption of Dazu lithographic sandstone are small. The difference between the open porosity and the total porosity is not significant, corresponding to the difference between the free water absorption rate and the saturated water absorption rate (that is, the saturated water coefficient is large). These characteristics result in sandstone being vulnerable to the influence of water and salt in water, and slightly weaker in weathering resistance. (2) by testing the compressive strength of fresh cores, and referring to the quantitative classification criteria for weathering degree of the fourth edition of the Manual of Engineering Geology, The quantitative evaluation system of weathering degree of Dazu stone engraved sandstone material is obtained. However, each test index has its own advantages and disadvantages. Comprehensive evaluation of the research object by using a variety of indicators can effectively avoid the limitation of a single index. (3) the changes of mineral and chemical compositions accompany the weathering process of Dazu lithographic sandstone material. The decomposition of calcite and dolomite and the decrease of oxide loss of Na,Mg,Ga,K. The selected mineral weathering index (Wck,) and four chemical weathering indices can indicate the weathering degree of Dazu lithographic sandstone materials. Dazu lithographic sandstone materials contain a certain amount of clay minerals (mainly Illite, Illite, mixed layer minerals, chlorite, green mixed layer minerals). These clay minerals have the characteristics of water absorption, water loss and shrinkage, which can easily lead to sandstone weathering.
【学位授予单位】：兰州大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：K877.4;P512.1

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