黄土节理的强度与渗流问题研究

发布时间：2018-03-22 14:55

本文选题：黄土　切入点：节理　出处：《西安建筑科技大学》2014年博士论文　论文类型：学位论文

【摘要】：节理是黄土地区普遍存在的一种地质现象。节理的存在破坏了土体的整体性和连续性。节理面是剪切弱面，会使水分运动加快，，对黄土地区洞室和边坡的稳定构成安全隐患。目前对节理的研究多集中在其地质属性上，而工程性质的研究尚不足，尚缺乏黄土节理剪切和渗流特性的研究文献。基于此本文对黄土节理的剪切性质和渗流性质展开研究工作。通过对不同含水率、干密度以及表面形态的黄土节理进行直剪试验，研究了黄土节理强度参数变化规律。结果表明：黄土节理内摩擦角随含水率呈开口向下的抛物线形态变化。存在一个界限含水率，使土样的含水率为该界限值时，节理面的摩擦角最大。在低含水率时节理表面形态对粘聚力的影响较大。粗糙节理面的粘聚力明显大于平整节理面。随着含水率的逐渐升高，表面形态对节理面粘聚力的影响逐渐减小。通过室内节理变水头试验、表面饱和入渗试验以及现场节理渗水试验研究了黄土节理的渗流性质。结果表明：黄土中有节理存在时，其流动仍然可以用达西定理来描述，但随着水头的增大，试验结果逐渐偏离达西定律；在表层饱和入渗的情况下，节理对水分入渗有促进作用，其渗透性随着节理开度的增大而增大；现场节理入渗试验表明黄土中的垂直节理在入渗初期具有高渗透性。黄土沿节理方向的入渗速度远大于水平方向的入渗速度。对黄土节理渗流问题进行了理论分析。黄土节理渗流属于沿节理方向入渗和垂直于节理方向往黄土体入渗的二维渗流问题。考虑节理内流体向土体的入渗及土体自身流速的影响，建立了黄土节理二维渗流模型，采用欧拉变数法推导了流体元运动微分方程，得到了以流速为函数的渗流微分方程。进而基于黄土节理渗流特征及边界条件，推导得到黄土节理二维稳态流的流量方程，表明岩体节理立方定律可归结为此方程在特定条件下的简化形式。进一步结合达西定律推导得到黄土节理渗透系数的表达式。考虑水分沿黄土节理的二维运动时，因为有水平向流动的影响，流体的广义阻力增大。建立了黄土节理渗流问题的数值分析方法。首先给出了黄土节理二维渗透系数矩阵，并建立了当考虑黄土中节理的存在时，水分场数值计算的模型。随后针对现有的在非饱和土体水分场数值计算中普遍存在的不考虑主渗透系数与坐标轴不重合的情况，采用四边形一次等参元研究建立了非饱和土体瞬态渗流的有限元算法。最后运用该数值模型和算法对多种边界条件下的黄土节理二维水分入渗问题进行了数值计算。验证了模型的适用性，并得到了节理入渗过程中湿润峰运动规律。
[Abstract]:Joint is a common geological phenomenon in loess area. The existence of joint destroys the integrity and continuity of soil. The stability of caverns and slopes in loess area is a safety hazard. At present, the study of joints is mostly focused on its geological properties, but the study of engineering properties is still insufficient. There is a lack of literature on the shear and seepage characteristics of loess joints, based on which the shear and seepage properties of loess joints are studied. Through the direct shear test of loess joints with different moisture content, dry density and surface morphology, The variation law of the strength parameters of loess joints is studied. The results show that the internal friction angle of loess joints varies with the moisture content in the parabola. There is a limit moisture content, when the moisture content of the soil sample is the limit value, The friction angle of joint surface is the largest. The influence of surface morphology on cohesion is greater at low moisture content. The cohesion of rough joint surface is obviously greater than that of flat joint surface. The effect of surface morphology on the cohesion of joint surface decreases gradually. The seepage properties of loess joints are studied by laboratory tests of joint head change, surface saturation infiltration test and field joint seepage test. The results show that the flow of loess joints can still be described by Darcy's theorem when joints exist in loess. However, with the increase of water head, the experimental results deviate from Darcy's law gradually, in the case of surface saturated infiltration, joints promote water infiltration, and its permeability increases with the increase of joint opening. The in-situ joint infiltration tests show that the vertical joints in loess have high permeability in the early stage of infiltration, and the infiltration velocity along the joint direction of loess is much higher than that in horizontal direction. The seepage problem of loess joint is analyzed theoretically. The seepage of loess joint belongs to the two dimensional seepage problem, which is perpendicular to the joint direction and to the loess body perpendicular to the joint direction. The infiltration of fluid into soil and soil in the joint are considered. The effect of body velocity, The two-dimensional seepage model of loess joints is established, and the differential equation of fluid element motion is derived by using Eulerian variable method, and the differential equation of seepage flow with velocity as function is obtained, which is based on the seepage characteristics and boundary conditions of loess joints. The flow equation of two-dimensional steady flow in loess joints is derived. It is shown that the cubic law of rock mass joints can be reduced to the simplified form of the equation under certain conditions. Furthermore, the expression of permeability coefficient of loess joints is derived by combining Darcy's law. When considering the two-dimensional movement of water along loess joints, Because of the influence of horizontal flow, the generalized resistance of the fluid increases. The numerical analysis method for the seepage problem of loess joints is established. Firstly, the two-dimensional permeability coefficient matrix of loess joints is given, and when the existence of joints in loess is considered, The model of numerical calculation of water field. Then, the existing numerical calculation of unsaturated soil water field does not consider that the principal permeability coefficient does not coincide with the coordinate axis. The finite element method for transient seepage of unsaturated soil is established by using quadrilateral isoparametric element method. Finally, the numerical model and algorithm are used to calculate the two-dimensional water infiltration problem of loess joints under various boundary conditions. The applicability of the model is verified. The movement law of wetting peak in the process of joint infiltration is obtained.
【学位授予单位】：西安建筑科技大学
【学位级别】：博士
【学位授予年份】：2014
【分类号】：TU444

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