A standard stress path triaxial test system was applied to carry out conventional triaxial shearing tests for gravelly sands under confining pressures ranging from 50 kPa to 400 kPa at the initial relative densities of 0.15, 0.35, 0.55, and 0.75, respectively. The test results show that all the samples of gravelly sand present strain hardening and shear contraction during the process of shearing test. Additionally, gravelly sands are significantly affected by the initial relative density. The hardening degree of gravelly sand samples rises in line with increasing initial relative densities during shearing tests. When initial relative densities D_r are at 0.15 and 0.35, the volume shrinkage of samples decreases with the increasing confining pressures. Instead, when initial relative densities D_r are at 0.55 and 0.75, the volume shrinkage of samples increases with the growth of confining pressures. To describe these triaxial shearing mechanical properties of gravelly sands, a higher-order dilatancy equation was proposed based on the concept of a super yield surface. A constitutive model which can describe the mechanical properties of gravelly sand was established when the associated flow laws were applied to compare with the results of the triaxial shearing test under the consolidated drained condition. The comparison results showed that the proposed model can reflect the strain hardening and shear contraction characteristics of gravelly sands from low to high confining pressures under different initial relative densities.

中文翻译：

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基于高阶剪胀方程的饱和砂砾岩本构模型

应用标准应力路径三轴试验系统，在初始相对密度分别为0.15、0.35、0.55和0.75的限制压力为50 kPa至400 kPa的情况下，对砾石砂进行常规的三轴剪切试验。试验结果表明，所有砾石砂样品在剪切试验过程中均出现应变硬化和剪切收缩现象。另外，砾石砂受到初始相对密度的显着影响。在剪切试验期间，砾石砂样品的硬化程度与初始相对密度的增加一致。当初始相对密度D _r为0.15和0.35时，样品的体积收缩随围压的增加而减小。相反，当初始相对密度D _r为0.55和0.75时，样品的体积收缩率随围压的增加而增加。为了描述砾石砂的这些三轴剪切力学特性，基于超屈服面的概念，提出了一个高阶剪胀方程。当应用相关的流动规律与固结排水条件下的三轴剪切试验结果进行比较时，建立了可以描述砾石砂土力学特性的本构模型。比较结果表明，所提出的模型可以反映出在不同初始相对密度下，低，高围压下砾石砂的应变硬化和剪切收缩特性。