弱胶结西域砾岩细观组构及其力学性能演化机理研究

Weakly cemented Xiyu conglomerates often exposed as steep valley slopes in nature. This landform obviously discrepancies to the poor cemented, low strength and easily weathered mechanical characteristics of Xiyu conglomerate. However, the essential knowledge of the contradiction of the geomorphological phenomenon to the mechanical characteristics of Xiyu conglomerate is still insufficient. The microfabric characteristics and evolution mechanism of the mechanical behavior of weakly cemented Xiyu conglomerates need to be researched. Environmental scanning electron microscopy, CT visualization triaxial test and digital image processing technologies are intended to be used in this project. The gravel content, cements characteristics and porosity characteristics are researched to reveal the heterogeneity characteristics of the Xiyu conglomerates. In order to ascertain the mesoscopic structure characteristics of the Xiyu conglomerates, the distribution of particles, the skeleton arrangement features and the contact relationships are also studied. Then, CT visualization triaxial tests are carried out. According to Stress - strain curve and the evolution laws of the mesoscopic structure characteristics, the damage evolution equation of load-microfabric parameters- macro mechanical parameters will be established and the evolution mechanism of the mechanical behavior of the weakly cemented Xiyu conglomerate would be revealed. Through the study of this project, it will be useful to improve the essential knowledge of the mechanical behavior of weakly cemented Xiyu conglomerate, and it will be able to ensure the safety of major projects in Xiyu conglomerate regions. So on, this research has important theoretical significance and application value.

弱胶结西域砾岩常以陡峻谷坡形态出露，与其胶结差、强度低、易风化的力学特性明显不符。目前有关于这种地貌现象与力学性能相矛盾的本质认识尚具有一定的局限性，亟需对西域砾岩细观组构特征及其力学性能演化机理展开研究并取得突破。本课题拟采用环境电镜扫描、CT可视化三轴试验、数字图像处理等技术，研究西域砾岩砾石含量、胶结物性状与孔隙率特性，揭示西域砾岩物质组成的非均质特性；研究西域砾岩的颗粒分布规律、骨架排列特征与接触关系，揭示西域砾岩细观空间结构特征；基于CT可视化三轴试验，研究西域砾岩的应力-应变曲线特征与孔隙、裂纹等细观结构性状的变化发展规律，建立西域砾岩荷载-细观组构参数-宏观力学特征参数的损伤演化方程，揭示西域砾岩力学性能演化机理。开展本项目研究，从细观组构性状变化的角度揭示西域砾岩力学性能演化机理，对于提高西域砾岩力学性能的本质认识，确保重大工程建设安全，具有重要的理论意义和应用价值。

弱胶结西域砾岩广布于天山南北两麓与昆仑山北麓，具有物质成分复杂、胶结差、强度低、易风化、遇水泥化等特性。由于对西域砾岩的结构及力学特性的认识不足，大大制约了天山经济带内相关工程的开发建设与地质环境防灾减灾。本项目以新疆天山北麓弱胶结西域砾岩为研究对象，开展了物质组成、结构特征与力学性能研究。在西域砾岩物质组成特征研究方面，查明西域组砾岩由粒径不同的粗碎粒屑组成，主要包括砾石、杂基、胶结物、孔隙四部分。其中砾石等大颗粒成份以花岗岩、凝灰岩、板岩、片岩为主，胶结物主要由石英、绿泥石、斜长石、伊利石等矿物组成，化学成分以SiO2，Al2O3，TFe2O3为主。试验获得西域砾岩天然密度为2.30 g/cm3~2.46g/cm3，孔隙率平均值约为15%，天然含水率2%~5%，并且埋深越大，其天然密度也越大孔隙率越低。在西域砾岩宏细观空间结构特征研究方面，获得西域砾岩颗粒级配特征，不均匀系数Cu为65.9~83.4，曲率系数Cc为2.38~ 3.35，级配良好。西域砾岩粗颗粒具有定向排列特征，并划分为颗粒悬浮结构和颗粒支撑结构两种结构类型。西域砾岩胶结物的微观结构为由块状颗粒堆积而成，表面光滑且致密平整，存有少量孔隙。在西域砾岩力学性能演化机理研究方面，通过室内外岩体力学试验获得西域砾岩变形模量为0.225GPa~3.78GPa，并表现出明显的尺寸效应与各向异性特征。受砾石颗粒排列特征的影响，铅直变形模量最大，颗粒短轴方向的变形模量次之，颗粒长轴方向变形模量最小，并且随着应力水平增加，西域砾岩呈现出各向同性的变形趋势。西域砾岩的抗压强度随着围压的增加表现出一定的非线性关系，可采用分段莫尔-库伦强度准则或幂函数型莫尔强度准则表征西域砾岩抗剪强度。西域砾岩抗剪强度由砾石颗粒间的内摩擦角以及由胶结物和水膜的分子引力所产生的粘聚力共同组成，并且与固结成岩作用的强弱、胶结程度的好坏密切相关。通过本项目研究初步获得了西域砾岩结构性状、不同荷载作用下力学特性与破坏机理，可为我国西部水利水电、交通等工程的建设和发展，提供重用科学支撑。