摘 要

黄土高原地区的黄土台塬大量的农业引水灌溉水事活动，地下水位逐渐抬高，改变了黄土台塬塬边斜坡渗流场，使坡体内部区域的土体处于渗流和剪切叠加作用，强烈影响着土体的力学和水理特性。论文以泾阳南塬饱和黄土为研究对象，通过开展饱和原状和重塑黄土的三轴渗透-剪切试验，研究不同围压状态、不同渗透压力条件下饱和黄土试样渗透特性和剪切强度性状，探讨泾阳南塬饱和黄土渗透-剪切机理，取得结论如下：

（1）三轴渗透-剪切试验过程中，饱和黄土试样渗透系数先急剧减小再减小趋势相对缓慢趋于基本不变；低围压状态下，随着轴向应变增加，饱和黄土试样渗透系数曲线降幅较大，而高围压状态下则降幅相对微小；不同渗透压力条件下饱和黄土试样渗透系数变化范围呈前大后小规律；渗透-剪切试验初期，饱和原状黄土试样渗透系数远大于饱和重塑黄土试样，随着渗透-剪切的继续进行，饱和原状黄土试样渗透系数降低幅度相对显著，最终饱和黄土试样渗透系数曲线逐渐重合。

（2）随着渗透压力增大，饱和黄土试样偏应力出现了不同程度的降低；其应力-应变曲线由三轴渗透-剪切试验初期相接近，继而出现趋于分离，不同围压状态对其分离程度影响不同；饱和黄土试样剪切强度随围压增大而显著增大，随渗透压力增大而降低；随渗透压力增大，饱和黄土试样总应力下黏聚力显著降低，而有效粘聚力降低相对较小，相同渗透压力条件下，饱和原状黄土试样黏聚力和有效黏聚力分别小于相应地饱和重塑黄土试样；饱和黄土试样内摩擦角随渗透压力增大而略有降低。

（3）饱和黄土试样三轴渗透-剪切试验中，其渗透性变化机理主要取决于剪切作用下土颗粒相互移动而处于动态调整排列，进而使其孔隙发生改变，同时，不同围压状态时渗透压力作用下水的渗透流动的动能对土颗粒的冲蚀，进而引起其结构性改变，最终影响饱和黄土渗透性；其剪切强度变化机理取决于波动的孔隙水压力对土颗粒进行持续冲蚀，可使土颗粒之间的联结遭受破坏而结构逐渐溃散，使其黏聚力显著降低，同时，水动能携裹土颗粒移动，降低了土颗粒之间相互挤压咬合的摩擦力，使其摩擦角略有降低。因此，受应力场与渗流场耦合作用，故对饱和黄土剪切强度产生劣化效应。

                                          Abstract

A large number of agricultural water diversion and irrigation activities in the loess plateau of the Loess Plateau, the groundwater level gradually increased, changed the seepage field of the slope of the loess plateau, and made the soil in the inner region of the slope under the superimposed effect of seepage and shear. Affect the mechanical and hydraulic properties of the soil. This thesis takes the saturated loess in the southern plateau of Jingyang as the research object, and studies the permeability and shear strength properties of saturated loess samples under different confining pressures and different osmotic pressures by carrying out triaxial permeability-shear tests of saturated undisturbed and remolded loess , To discuss the permeability-shear mechanism of saturated loess in South Jingyang Plateau, and the conclusions are as follows:

(1) During the triaxial penetration-shear test, the permeability coefficient of the saturated loess sample decreases sharply first and then decreases relatively slowly and tends to be basically unchanged; in the low confining pressure state, as the axial strain increases, the saturated loess sample The permeability coefficient curve of the sample has a large decrease, while the decrease is relatively small under high confining pressure; the variation range of the permeability coefficient of the saturated loess sample under different seepage pressure conditions is large and small; at the beginning of the permeability-shear test, saturated undisturbed loess The permeability coefficient of the sample is much larger than that of the saturated remolded loess sample. As the infiltration-shearing continues, the permeability coefficient of the saturated undisturbed loess sample decreases relatively significantly, and the permeability coefficient curve of the saturated loess sample gradually overlaps.

(2) As the seepage pressure increases, the deviator stress of the saturated loess sample decreases to different degrees; the stress-strain curve approaches from the initial stage of the triaxial permeability-shear test, and then tends to separate, and the confining pressure states are different. The degree of separation is different; the shear strength of the saturated loess sample increases significantly with the increase of confining pressure, and decreases with the increase of osmotic pressure; with the increase of osmotic pressure, the cohesive force of the saturated loess sample under the total stress decreases significantly , While the effective cohesion is relatively small. Under the same seepage pressure, the cohesion and effective cohesion of the saturated undisturbed loess samples are respectively smaller than the corresponding saturated remolded loess samples; the internal friction angle of the saturated loess samples increases with the infiltration The pressure increases and decreases slightly.

(3) In the triaxial permeability-shear test of saturated loess samples, the permeability change mechanism mainly depends on the mutual movement of soil particles under shear action and dynamic adjustment of the arrangement, which in turn causes the pores to change. At the same time, different confining pressures In the state, the kinetic energy of the seepage flow of water under the action of osmotic pressure erodes the soil particles, which in turn causes its structural changes, and ultimately affects the permeability of saturated loess; its shear strength change mechanism depends on the continuous pore water pressure on the soil particles. Erosion can damage the connection between soil particles and gradually disintegrate the structure, so that the cohesion force is significantly reduced. At the same time, the water kinetic energy carries the soil particles to move, reducing the friction between the soil particles when they squeeze and bite each other. The friction angle is slightly reduced. Therefore, the coupled effect of the stress field and the seepage field will degrade the shear strength of saturated loess.

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