石英云母片岩各向异性特征及其对围岩稳定性影响的研究

发布时间：2018-08-19 19:19

【摘要】：岩石在其成岩及后期次生演化过程中，形成了诸如层理、片理、节理及断层等原生或次生结构面，正是由于这些成岩缺陷和构造损伤的存在，使得岩石或岩体呈现明显的各向异性特征。石英云母片岩具有片状构造，它所表现出的力学各向异性特征主要受控于岩石的矿物组成和排列组合方式，此特征对地下洞室稳定性具有显著影响。本文以丹巴水电站石英云母片岩为研究对象，通过微观结构及宏观物理力学特性试验，并结合大量的现场调查和分析，以工程地质分析评价为主线，运用构造地质学、矿物岩石学、岩体力学、断裂力学、各向异性理论等多种理论方法，准确地把握了石英云母片岩的各向异性及其对围岩稳定性的影响。通过上述研究本文主要取得以下成果：（1）现场地质调查表明：研究区在印支、燕山和喜山期经历了多期次变质活动的叠加改造，构造作用极为复杂，区内以剥蚀中-高山地貌为主，最大地应力近水平且其值处于中等偏高级应力量级，地下水不发育且以具一定的埋深基岩裂隙水为主。CPD1平洞围岩（石英云母片岩）片理密集发育，强度较低，为软质岩，平洞自开挖至今未支护，整体稳定性较好。（2）通过铸体磨片试验和扫描电镜试验对石英云母片岩矿物组成及微观结构进行研究，揭示了石英云母片岩呈现各向异性的微观机理。首先，通过对CPD1平洞42组磨片试验统计分析可得，平洞围岩矿物以片状云母、粒状石英为主，矿物组成随洞深呈现规律性变化。其次，采用电镜扫描对石英云母片岩进行鉴测表明，片状和粒状矿物呈现定向排列，且晶粒间或其内部存在晶粒边界、晶格断裂、微裂隙等多种定向性微弱面。最后，结合地质成因分析可知，石英云母片岩组构单元经历了漫长的地质年代，这使得其内部矿物颗粒及微弱面具有矿物晶格和形状优势取向，从而使得石英云母片岩从宏观和微观均呈现出各向异性的特征。（3）结合岩体各向异性理论，并采用单轴抗压强度试验、三轴卸载试验、原位直剪试验及现场声波测试对石英云母片岩宏观物理力学各向异性进行研究。单轴压缩试验表明：随着β值的增大，石英云母片岩的单轴抗压强度与弹性模量均有先减少后增大的趋势，呈“U”型，约在β=30°时，两者均达到最小值；试样的破坏模式主要为张拉破坏，并且破坏特征受控于片理与加载方向。三轴卸荷试验结果表明：石英云母片岩在卸荷作用下其强度及变形均存在各向异性特性，且随着围压的增大石英云母片岩各向异性逐渐减弱；岩样破坏模式均为穿层剪切破坏。现场声波测试表明：石英云母片岩波速具有各向异性特征，沿顺片理方向波速最高，沿垂直片理方向波速最低，其他方向的波速介于此两者之间；岩样从上部到下部波速明显增高，且各向异性指数呈逐渐减少的趋势。现场岩石直剪试验表明：石英云母片岩剪切参数及岩样变形特征均具有显著的各向异性；平行片理的抗剪断峰值强度参数f=0.61，C=0.84MPa，抗剪强度参数f′=0.45，C′=0.30MPa，试样几乎都有切层破坏现象；垂直片理的抗剪断峰值强度参数f=0.76，C=2.75MPa，抗剪强度参数f′=0.69，C′=0.23MPa，试样大多数剪切面都有1~3cm的起伏。（4）通过现场地质调查收集CPD1平洞相关地质资料，并基于断裂力学理论从微观和宏观角度对围岩稳定性的影响因素进行分析。从微观角度来说，石英云母片岩的矿物组成对围岩稳定性具有较明显的影响，对于围岩石英矿物含量越高，围岩力学性能越好，则围岩稳定性也就越好；除此平洞开挖后沿片理方向上易产生应力集中，该方向上的微裂纹易发生扩展或产生沿颗粒间的滑移。从宏观角度来说，影响围岩稳定的因素可以分为地质因素（岩体强度、岩体完整性、岩体结构、地应力、地下水等）和工程因素（开挖方式方法、洞室形状及尺寸等）。其中，岩体强度、地应力及开挖方式对围岩稳定性影响显著，为平洞围岩稳定性控制性因素。（5）通过现场地质调查，结合大量室内及现场试验数据统计分析。首先，作者认为石英云母片岩的片理是一种特殊的结构面，其各方面的性质已经在岩石纵波速度、岩石单轴饱和抗压强度等参数中得到了比较充分的反映，故片理不应与节理、断层破碎带等其他结构面一起参与岩体参数的划分或评定，并将平洞围岩的岩体结构类型定名为“似块状结构”；其次，，以水电工程围岩工程地质分类和围岩初步分类标准为基础，针对高地应力、岩体结构及片理产状进行修正，建立丹巴水电站地下洞室围岩初判标准；最后，根据围岩工程地质分类以及实际围岩类别、岩体变形与围岩类别分类标准，依据丹巴软岩岩质类型、岩体结构类型和岩体完整程度，并结合现场地质调查及监测资料，建立了适合丹巴地下洞室的软弱围岩分类体系—SRCS体系（Soft Rock Classification System）
[Abstract]:Primary or secondary structural planes such as bedding, schistosity, joints and faults are formed in the process of rock diagenesis and later secondary evolution. It is precisely because of these diagenetic defects and structural damage that the rock or rock mass exhibits obvious anisotropic characteristics. In this paper, the quartz mica schist of Danba Hydropower Station is taken as the research object, through the test of microstructure and macroscopic physical and mechanical properties, and combined with a large number of field investigation and analysis, the engineering geological analysis and evaluation are carried out. As the main line, the anisotropy of quartz-mica schist and its influence on the stability of surrounding rock are accurately grasped by many theoretical methods, such as tectonic geology, mineral petrology, rock mass mechanics, fracture mechanics and anisotropy theory.
(1) Field geological survey shows that the study area underwent multi-stage metamorphic superimposition in Indosinian, Yanshan and Himalayan periods, and the tectonic process was extremely complex. The area was dominated by denuded middle-alpine landforms, the maximum geostress was near the level and its value was in medium-to-high-grade stress magnitude, and the groundwater was undeveloped and the bedrock fissures with certain buried depth were found. The surrounding rock (quartz mica schist) of CPD1 flat cave is densely developed and has low strength. It is soft rock. The flat cave has not been supported since excavation, and the overall stability is good.
(2) The mineral composition and microstructure of quartz-mica schist were studied by casting grinding test and scanning electron microscope test, and the mechanism of anisotropy of quartz-mica schist was revealed. Firstly, through the statistical analysis of 42 groups of grinding test of CPD1 flat cave, it was found that the surrounding rock minerals of flat cave were mainly lamellar mica, granular quartz and mineral composition was mainly granular quartz. Secondly, the quartz-mica schist is characterized by directional alignment of schist and granular minerals, and there are grain boundaries, lattice fractures, micro-cracks and other orientational facets between or within the grains. Finally, combined with the analysis of geological genesis, the fabric unit of quartz-mica schist is known. After a long geological age, the mineral grains and faint faces in the quartz-mica schist have the predominant orientation of mineral lattice and shape, which makes the quartz-mica schist exhibit anisotropic characteristics both macroscopically and microscopically.
(3) The macroscopic physical and mechanical anisotropy of quartz-mica schist is studied by uniaxial compressive strength test, triaxial unloading test, in-situ direct shear test and in-situ acoustic wave test. Uniaxial compressive test shows that the uniaxial compressive strength and elastic modulus of quartz-mica schist increase with the value of beta. The results of triaxial unloading test show that the strength and deformation of quartz-mica schist are anisotropic under unloading, and the failure mode is mainly tensile failure, and the failure characteristics are controlled by the direction of sheeting and loading. With the increase of confining pressure, the anisotropy of quartz-mica schist gradually weakens, and the failure modes of rock samples are shear failure through layers. The in-situ direct shear tests show that the shear parameters and deformation characteristics of quartz-mica schist have significant anisotropy, and the peak shear strength parameters of parallel schist f = 0.61, C = 0.84MPa, shear strength parameters f'= 0.45, C'= 0.30MPa. The peak shear strength parameter f = 0.76, C = 2.75 MPa, shear strength parameter f'= 0.69, C'= 0.23 MPa, and most of the shear planes of the specimens fluctuate from 1 cm to 3 cm.
(4) Based on the fracture mechanics theory, the factors influencing the stability of surrounding rocks are analyzed from the micro and macro aspects. From the micro point of view, the mineral composition of quartz-mica schist has obvious influence on the stability of surrounding rocks. The higher the content of quartz minerals in surrounding rocks, the higher the content of quartz minerals in surrounding rocks. The better the mechanical properties of rock, the better the stability of surrounding rock; besides, the stress concentration along the cleavage direction is easy to occur after excavation of the flat tunnel, and the micro-cracks in this direction are easy to expand or slip along the grain. From a macroscopic point of view, the factors affecting the stability of surrounding rock can be divided into geological factors (rock strength, rock integrity, rock mass consolidation). Structure, in-situ stress, groundwater, etc.) and engineering factors (excavation method, cavern shape and size, etc.). Among them, rock mass strength, in-situ stress and excavation method have significant influence on the stability of surrounding rock, and are the controlling factors of the stability of surrounding rock of flat cavern.
(5) Through on-site geological survey and statistical analysis of a large number of laboratory and field test data, the author considers that the schistosity of quartz-mica schist is a special structural plane whose properties have been fully reflected in the parameters of P-wave velocity and uniaxial saturated compressive strength of rock, so schistosity should not be associated with joints. Other structural planes, such as fault fracture zones, participate in the division or evaluation of rock mass parameters, and name the rock mass structure type of the surrounding rock of Pingdong Tunnel as "block-like structure"; secondly, based on the engineering geological classification of surrounding rock of hydropower engineering and the preliminary classification standard of surrounding rock, the high geostress, rock mass structure and schistosity occurrence are modified and constructed. Initial criteria for surrounding rock of underground cavern of Lidanba Hydropower Station; Finally, according to engineering geological classification of surrounding rock, actual surrounding rock classification, rock mass deformation and classification criteria of surrounding rock, according to soft rock type, rock mass structure type and rock mass integrity of Danba Hydropower Station, combined with on-site geological survey and monitoring data, an underground cavern suitable for Danba Hydropower Station is established. Classification system of weak surrounding rock in the room -- SRCS system (Soft Rock Classification System)
【学位授予单位】：成都理工大学
【学位级别】：硕士
【学位授予年份】：2014
【分类号】：TU45

【参考文献】