Sand-clay mixtures are often encountered in natural deposits and compacted soils in earth structures in the form of gap-graded soils. They commonly display anisotropic fabric which markedly influences their wave propagation and mechanical properties. In this study, a comprehensive experimental program is carried out to thoroughly examine the influence of the inclined bedding plane and clay type on the small strain shear modulus (G_max) of granular soils mixed with various portions of low and high plasticity fines, controlling in this way the double diffuse layer of the microparticles. To this end, cylindrical samples containing different fines contents are prepared with their corresponding optimum water contents and maximum dry densities in a standard proctor mold. Undisturbed specimens are then extracted by the continuous coring method and wave propagation tests with bender elements are applied at different angles with respect to the bedding plane (α-direction), evaluating in this way shear wave velocity and G_max. The test results suggested that α-direction has a significant influence on G_max of sand-clay mixtures and this influence is amplified at lower fines contents and higher confining pressures. Mixtures of sand with high plasticity clay are observed to have lower degree of anisotropy compared to those containing low plasticity clay, specifically at lower confining pressures. The contribution of fines in the load carrying structure of the solid skeleton decreases for high plasticity clays; the phenomenon which is primarily attributed to the thick diffuse double layer of the microparticles. This trend becomes more pronounced at higher contents of fines inclusion where the sand-in-fine structure dominates. A previously proposed expression for sands is rectified and extended so as to develop a G_max model of sand-cohesive clay mixtures taking into account the bedding plane direction. Micromechanical-based interpretations are further elaborated considering the intervention of the microparticles on the contact response of sand grains altering their normal and tangential contact behavior, so as to supplement the findings, from the wave propagation tests, with multi-scale insights.

砂粘土混合物经常以间隙级配土壤的形式出现在自然沉积物和地球结构中的压实土壤中。它们通常显示出显着影响其波传播和机械性能的各向异性织物。在本研究中，开展了一项综合试验计划，以彻底检验倾斜层理面和粘土类型对小应变剪切模量 ( G _max) 混合了不同部分的低塑性和高塑性细粒的颗粒土壤，以这种方式控制微粒的双扩散层。为此，在标准 Proctor 模具中制备含有不同细粉含量的圆柱形样品，并具有相应的最佳含水量和最大干密度。然后通过连续取芯方法提取未受干扰的样本，并以相对于层理平面（α方向）的不同角度应用弯曲元件进行波传播测试，以这种方式评估剪切波速度和G _max。测试结果表明α-方向对G _max有显着影响砂粘土混合物，这种影响在较低的细粒含量和较高的围压下被放大。与含有低塑性粘土的砂子相比，观察到砂子与高塑性粘土的混合物具有较低的各向异性程度，特别是在较低的围压下。对于高塑性粘土，细粒在固体骨架承载结构中的贡献减小；这种现象主要归因于微粒的厚扩散双层。这种趋势在细粒夹杂物含量较高的情况下变得更加明显，其中细砂结构占主导地位。对先前提出的沙子表达式进行了修正和扩展，以开发出G _max考虑层理平面方向的砂粘性粘土混合物模型。考虑到微粒对改变其法向和切向接触行为的砂粒接触响应的干预，进一步阐述了基于微观力学的解释，以补充来自波传播测试的多尺度见解。