峨眉山玄武岩结构体风化特征研究

发布时间：2018-11-20 10:19

【摘要】：我国西南地区广泛分布着峨眉山玄武岩,该区域炎热多雨的气候,特别有利于岩石的化学风化,风化的岩石与新鲜岩石在完整性、矿物组成、力学特性等差异特别显著。风化的岩石是滑坡、泥石流、石漠化等地质灾害最重要的物质来源之一,同时风化岩体的建基面及其所取的最优值是岩土工程师们、设计者们长期关注的问题。本文以峨眉山玄武岩斜坡非饱和带低渗透性的结构体作为研究对象,通过野外调查以及室内试验例如：SEM、薄片鉴定、岩石全化学分析等,系统、深入的分析了风化过程中岩石的宏微观特征、矿物组成、化学元素移动性等的变化规律。风化结构体呈现明显的圈层结构,外层为腐岩,内部为核心石,风化程度由内向外明显增大,核心石与腐岩壳三维界线区域突变特别显著,核心石表面溶蚀不明显,孔隙、裂隙不发育。然而,腐岩表面溶蚀严重,造岩矿物如斜长石等粘土化现象明显,可观察到矿物呈不规则的鳞片状,孔隙极其发育。在风化程度较低的风化前期,Fe2O3的含量增加明显而FeO的含量亏损显著,其他元素的迁移性行为并不明显或者说对于风化程度的变化敏感性并不显著。风化程度较高的风化中、后期,岩石的主量元素如活动性相对较弱的如Al等、迁移性较强的Na、Ca等以及不同价态的Fe其行为与风化程度的变化敏感性显著,两者之间关系明确简单,同时表征岩石物理力学参数如密度、孔隙度、抗压强度等随着风化的进行也在显著变化,即使是微风化的玄武岩,相对于母岩而言,完整性、宏观特征无明显差异,但是,力学强度却发生了急剧的减少,这可从微观观察到的微裂隙发育以及结构面出现的铁质渲染物质解释强度减小的原因。在上述研究的基础上,根据结构体风化过程中主量元素的迁移特征,提出了新的风化指数：A-FM风化指数,对比既有的风化指数如CIW、CIA、R等,无论是风化程度较低的前期还是风化程度较高的中、后期,A-FM指数与岩石的风化程度关系简单明确,敏感性显著,因此,A-FM指数可作为玄武岩风化程度评价的重要依据。
[Abstract]:Emeishan basalts are widely distributed in southwest China. The hot and rainy climate in this area is especially conducive to the chemical weathering of rocks, and the differences between weathered rocks and fresh rocks in integrity, mineral composition and mechanical properties are particularly significant. Weathered rock is one of the most important sources of geological hazards, such as landslide, debris flow, rocky desertification, etc. At the same time, the foundation surface of weathered rock body and its optimum value are the problems that geotechnical engineers and designers pay close attention to for a long time. In this paper, the low permeability structure in the unsaturated zone of the Emeishan basalt slope is taken as the research object. Through field investigation and laboratory tests, such as SEM, sheet identification, rock total chemical analysis, etc. The changes of macro and micro characteristics, mineral composition and mobility of chemical elements during weathering are analyzed. The weathering structure shows obvious circle structure, the outer layer is saprophyte, the inner part is the core stone, the weathering degree increases obviously from inside to outside, the abrupt change of three-dimensional boundary area between core stone and saprophyte crust is especially remarkable, the surface dissolution of core stone is not obvious, and the pore is not obvious. The fissures are not developed. However, the surface of the saprophyte is seriously corroded, and the clay-forming phenomena of rock-forming minerals such as plagioclase are obvious. The minerals can be observed to be irregular scales, and the pores are extremely developed. In the early stage of weathering with low weathering degree, the content of Fe2O3 increased obviously, the content of FeO decreased significantly, and the migration behavior of other elements was not obvious or sensitive to the change of weathering degree. In the weathering with higher weathering degree, in the late stage, the main elements of rock such as relatively weak activity such as Al, Na,Ca with strong migration, and Fe with different valence states are sensitive to the change of behavior and weathering degree. The relationship between the two is clear and simple, and the physical and mechanical parameters such as density, porosity and compressive strength of rock are also changed with weathering. There is no obvious difference in macroscopic characteristics, but the mechanical strength has been sharply reduced, which can be seen from the microscopic development of microcracks and the explanation of the intensity of the iron rendering material on the structure surface. On the basis of the above research, a new weathering index, A-FM weathering index, is proposed according to the migration characteristics of principal elements in the weathering process of structural bodies, and the existing weathering indices such as CIW,CIA,R, etc., are compared. The relationship between the A-FM index and the weathering degree of rock is simple and clear, and the sensitivity is significant, whether it is in the early stage of low weathering degree or in the middle weathering stage with high weathering degree, therefore, the relationship between the A-FM index and the weathering degree of rock is obvious. A-FM index can be used as an important basis for evaluating the weathering degree of basalt.
【学位授予单位】：昆明理工大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：P588.145

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