疏松砂岩工程地质特性研究

发布时间：2018-12-07 15:17

【摘要】：疏松砂岩是近年来重大地下工程中揭露一套结构疏松,自稳能力差,涌水、塌方等工程事故频发的岩层。针对目前对其工程地质性质研究的不足,本文以疏松砂岩为研究对象,依托多个已建和在建工程,通过野外调查,采用系统室内实验,分析归纳了疏松砂岩基本的工程地质特性,并对其冻结效应及成因问题进行了深入研究和探讨。从而补充并丰富了对疏松砂岩基础性状的研究,尤其是补充了其物理力学性质、结构特征等基础性规律及其机理,为岩土工程领域内疏松砂岩的进一步研究和工程建设提供理论及实验数据支持。本文获得以下几点结论：(1)疏松砂岩分布特征及物质成分的研究表明,疏松砂岩分布广泛,主要位于陇东区及陇中的兰州盆地内；属于红层中的一层或多层,为新近系及古近系沉积物；其物质成分单一,主要为石英,胶结物含量很少,杂质含量极少。(2)疏松砂岩结构及物理力学性质实验表明,其宏观上属于散体状结构似连续介质；微观上属于骨架状结构,胶结差,并构成均匀松散的孔隙结构类型：力学强度很低,岩性软弱,属于极软岩。疏松砂岩属于泥质粉(细)砂岩,结构松散,孔隙大；骨架颗粒分选好,且具一定磨圆度,以点触式接触为主；泥质胶结或微弱的钙质胶结；物理力学性质差,接近于松散砂,渗透性弱、易崩解,抗剪强度很低,压缩性低。(3)疏松砂岩冻结效应研究表明其物理力学性质、结构特征等均受到冻融作用的影响。物理性质中,含水特性、密度及渗透特性等均随着冻结状态改变而发生变化；冻融过程中的结构效应包括其整体结构的变化,微裂隙的新生,孔隙的变化及粘土矿物的变化等；冻结大大改善了其力学强度,而解冻后强度劣化,且低于天然状态。工程中应考虑并合理利用其冻融过程中物理力学性质变化规律。(4)疏松砂岩成因研究中各种特征综合表明,它属于一套风沙活动的产物,受后期赋存水环境作用的影响。疏松砂岩具有成岩作用较弱、成岩环境复杂等特征,是与干热气候相适应、形成于干旱气候环境下的风成沙产物,且受后期赋存环境及成岩作用的影响。并以此对新近系、古近系时期的干旱气候及环境问题进行了探讨。
[Abstract]:Loose sandstone is a kind of rock stratum which has been exposed in the important underground engineering in recent years, such as loose structure, poor self-stability, water gushing, collapse and other engineering accidents. In view of the deficiency of the present research on its engineering geological properties, this paper takes loose sandstone as the research object, relies on many existing building and construction projects, through field investigation, adopts systematic indoor experiments. The basic engineering geological characteristics of loose sandstone are analyzed and summarized, and the freezing effect and genetic problems are deeply studied and discussed. It complements and enriches the study of the basic characteristics of loose sandstone, especially the basic laws and mechanisms of physical and mechanical properties, structural characteristics, etc. To provide theoretical and experimental data for further research and engineering construction of loose sandstone in geotechnical engineering field. In this paper, the following conclusions are obtained: (1) the study of the distribution characteristics and material composition of loose sandstone shows that the loose sandstone is widely distributed, mainly located in the east of Gansu and Lanzhou basin in the middle of Gansu; Belonging to one or more layers of the red beds, which are Neogene and Paleogene sediments; Its material composition is single, mainly quartz, the content of cement is very little, impurity content is very few. (2) the structure and physical and mechanical properties of loose sandstone show that it belongs to the granular structure like continuum medium macroscopically; Microscopically, it belongs to skeleton structure, poor cementation, and forms uniform and loose pore structure type: low mechanical strength, weak lithology and very soft rock. Loose sandstone belongs to shaly silt (fine) sandstone with loose structure and large porosity. Physical and mechanical properties are poor, close to loose sand, weak permeability, easy to disintegrate, low shear strength and low compressibility. (3) the freezing effect of loose sandstone shows that its physical and mechanical properties and structural characteristics are affected by freeze-thaw process. In physical properties, the characteristics of water content, density and permeability change with the change of freezing state, and the structural effects in freezing and thawing process include the change of its whole structure, the creation of microcracks, the change of pores and the change of clay minerals, etc. Freezing greatly improved its mechanical strength, but its strength deteriorated after thawing and was lower than that of natural state. During the process of freeze-thaw, the variation of physical and mechanical properties should be taken into account and reasonably utilized. (4) the study on the genesis of loose sandstone shows that it belongs to the product of wind-sand activity and is affected by the effect of water environment in the later stage. Loose sandstone has the characteristics of weak diagenesis and complex diagenetic environment. It is the product of aeolian sand formed in arid climate and adapted to dry and hot climate. It is also affected by late occurrence environment and diagenesis. The arid climate and environment of Neogene and Paleogene were discussed.
【学位授予单位】：兰州大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：P642

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