岩土孔隙尺度水力耦合特性细观模拟研究

发布时间：2018-04-20 17:23

本文选题：岩土体 + 孔隙水压力　；参考：《武汉大学》2016年博士论文

【摘要】：目前,大规模资源开采、水利工程施工、二氧化碳的地下封存及高放射物的地质处置,都涉及到地下水和深部岩体的相互作用。深部地层中的岩土体在地下水变化时,孔隙水和裂隙水的渗透过程直接影响地层中的应力分布。在外部扰动荷载作用下,饱和岩土体易产生超孔隙水压力,将对岩土工程的安全与稳定造成极大的隐患。水力耦合问题一直是岩土工程中的重要课题,然而,仅从单一的宏观尺度来认识这一问题已经不能满足我国工程实践和基础科学研究的需求。本文从细观孔隙尺度上研究了颗粒形状的表征方法,定义了形状参数并详细阐述了形状参数-球度,及其与岩石的宏观力学特性的关系。针对颗粒离散元中的粘结接触模型,提出了考虑胶结厚度的孔隙度算法。改进了颗粒流程序中的流体耦合算法并进行了流体注入诱导的裂纹扩展研究。然后提出了颗粒-流体耦合的计算模型,解决了颗粒流程序中现有流体算法所面临的问。并采用该算法模拟了饱和土的三轴排水和不排水剪切试验。本文的主要研究成果如下：(1)定义了描述颗粒形状的形状参数-球度,球度定义为与颗粒等体积的球体表面积和颗粒表面积之间的比值。球度描述了一个颗粒和球体的接近程度,能够反映颗粒之间的咬合作用的强弱。通过生成四种代表颗粒研究了颗粒形状和岩石宏观力学特性的关系。结果表明矿物颗粒的形状影响岩石的启裂强度、损伤强度和峰值强度。具体来说,随着球度增大,特征强度指标均降低。随着颗粒球度的增大,试样的弹模降低,泊松比会增大。颗粒球度降低时,颗粒之间的咬合作用增强,试样的内摩擦角和粘聚力都呈增大趋势。(2)在颗粒流程序中的流体算法-固定网格法的基础上加入力学伺服模块,模拟了三轴渗流耦合试验,研究了全应力应变过程中渗透特性的变化规律。考虑到离散元模拟中孔隙度和真实试样的巨大差异,提出了考虑胶结厚度的孔隙度计算方法。计算结果表明所提算法能够反映真实孔隙度。同时,所提算法考虑裂纹扩展过程中接触粘结失效的问题,建立了孔隙度和裂纹数目之间的关系,并利用Kozeny-Carman方程推推导了渗透率的变化规律。结果表明采用新的孔隙度算法得出的全应力应变过程中渗透率变化曲线与其他学者在试验中得出的渗透率曲线一致。(3)对颗粒流程序中的流体耦合算法进行了改进,加入了流体流动对于颗粒的剪切力,并在计算中考虑了流体网络由于颗粒位移造成的网格体积的变化。采用双注水孔试样研究了流体注入诱导的裂纹扩展过程,阐述了注水孔间距对于裂纹生长模式、定向以及裂隙拓扑结构的影响。通过Dijkstra算法预测了两个注水孔之间的流体最短路径。计算结果表明,当注水孔间距较近时,微裂纹相互作用较强,微裂纹数目较多,裂隙网络连通性较差,从两个注水孔启裂的裂纹趋向于直接聚合；当注水孔间距较大时,裂隙网络连通性较好,微裂纹数目较少。裂纹方向基本上与压力力链垂直,在裂纹扩展尖端区域,张力力链较为集中。(4)基于前人的研究,提出了一种新的颗粒-流体耦合离散元计算模型,详细推导了超孔隙水压力的计算方法,阐述了水压力的作用机制。在模型中考虑了应变诱导的孔隙水压力及孔隙体积的变化,并对测量球的大小进行了优化,提高了计算效率。(5)在颗粒流平台下分三个模块实现了所提出的颗粒-流体耦合模型。通过北京黏质粉土的三轴不排水试验数据校准了颗粒的细观参数。将耦合模型计算得到偏应力曲线和孔隙水压力曲线与试验和常体积法的计算结果进行比较,发现耦合方法得到结果与试验及常体积法均一致。采用校准之后的细观参数,模拟了不同围压下饱和土的排水和不排水三轴压缩试验。结果表明,随着围压的升高,偏应力升高。在不排水条件下,应力比随着围压升高而降低,孔隙水压力随着围压升高而增大。
[Abstract]:At present, large-scale resource exploitation, water conservancy project construction, underground sealing of carbon dioxide and geological disposal of high radioactive materials all involve the interaction of groundwater and deep rock mass. In deep stratum, the infiltration process of pore water and fissure water directly affects the stress distribution in the stratum when the groundwater changes. Under the load, the saturated rock and soil can easily produce super pore water pressure, which will cause great hidden danger to the safety and stability of geotechnical engineering. The hydraulic coupling problem has always been an important subject in geotechnical engineering. However, it is impossible to meet the needs of the engineering practice and basic scientific research in our country only from a single macro scale. This paper studies the characterization of the shape of the particle from the meso pore size, defines the shape parameters and expounds the shape parameter sphericity, and its relation to the macroscopic mechanical properties of the rock. In view of the bond contact model in the particle discrete element, the aperture degree algorithm considering the cementation thickness is proposed. The fluid in the particle flow program is improved. The coupling algorithm is used to study the crack propagation induced by fluid injection. Then the calculation model of the particle fluid coupling is proposed to solve the problem of the existing fluid algorithm in the particle flow program. The three axis drainage and undrained shear test of the saturated soil is simulated with this algorithm. The main research results of this paper are as follows: (1) definition The degree of sphericity describing the shape parameter of the particle shape is defined as the ratio between the surface area of the sphere and the surface area of the particles. The sphericity describes the proximity of a particle and the sphere, which can reflect the strength of the occlusion between the particles. By generating four kinds of representative particles, the particle shape and macroscopic mechanics of the rocks are studied. The result shows that the shape of mineral particles affects the opening strength, the strength and the peak strength of the rock. In particular, with the increase of the sphericity, the index of the characteristic strength decreases. With the increase of the sphericity, the modulus of the specimen is reduced and the Poisson's ratio will increase. When the particle sphericity is reduced, the bite effect between particles is enhanced and the sample is enhanced. The internal friction angle and cohesive force are all increasing. (2) on the basis of the fluid algorithm fixed grid method in the particle flow program, the mechanical servo module is added, the three axis seepage coupling test is simulated, and the change law of the permeability characteristic in the full stress and strain process is studied. The great difference between the porosity and the true specimen in the discrete element simulation is taken into account. The porosity calculation method considering the thickness of cementation is proposed. The calculation results show that the proposed algorithm can reflect the true porosity. At the same time, the proposed algorithm takes into account the problem of contact failure in the process of crack propagation, establishes the relationship between the number of porosity and the number of cracks, and deduces the change law of permeability by using the Kozeny-Carman equation. The results show that the permeability change curve obtained by the new porosity algorithm is in accordance with the permeability curve obtained by other scholars in the experiment. (3) the fluid coupling algorithm in the particle flow program is improved, the fluid flow is added to the shear force of the particles, and the fluid network is considered in the calculation. The change of the mesh volume caused by the displacement of the particle is studied. The process of crack propagation induced by fluid injection is studied by the double injection hole specimen. The effect of the distance between the water injection hole on the mode of crack growth, the orientation and the topological structure of the crack is expounded. The shortest path between two water injection holes is predicted by the method of Dijkstra. The calculation results show that When the spacing of water injection holes is near, the interaction of micro cracks is stronger, the number of micro cracks is more, the connectivity of fracture network is poor, the crack initiation from two water injection holes tends to direct polymerization. When the spacing of water injection holes is large, the connectivity of the fracture network is better and the number of micro cracks is less. The crack direction is basically perpendicular to the pressure chain, and the crack propagation is extended. In the tip area, the tension chain is more concentrated. (4) based on the previous research, a new calculation model of particle fluid coupling discrete element is put forward. The calculation method of super pore water pressure is derived in detail, and the mechanism of water pressure is expounded. In the model, the changes of pore water pressure and pore volume induced by strain are taken into account, and the measurement ball is also measured. The size is optimized and the calculation efficiency is improved. (5) the proposed particle fluid coupling model is realized by three modules under the particle flow platform. The fine parameters of the particles are calibrated through the three axis undrained test data of the Beijing clay silt. The coupling model is calculated to get the partial stress curve and the pore water pressure curve and the test and constant. The results of the volume method are compared. It is found that the results of the coupling method are in agreement with the test and the normal volume method. The three axial compression tests of the drainage and undrained soil under different confining pressure are simulated with the calibrated parameters. The results show that the stress ratio increases with the rise of the confining pressure. Under the condition of undrained, the stress ratio is with the surrounding. The pore water pressure increases with the increase of confining pressure.

【学位授予单位】：武汉大学
【学位级别】：博士
【学位授予年份】：2016
【分类号】：TU43

【相似文献】