Undrained deformation of dilative sand generates negative excess pore pressure. It enhances the strength, which is called dilative hardening. This increased suction is not permanent. The heterogeneity at the grain scale triggers localisations causing local volume changes. The negative hydraulic gradient drives fluid into dilating shear zones. It loosens the soil and diminishes the shear strength. It is essential to understand the mechanism behind this internal drainage and to capture it numerically. The purpose of this paper is to develop a macroscopic constitutive relationship for the undrained deformation of saturated dense sand in the presence of a locally fully or partially drained shear band. Separate constitutive relations are generated for the band and intact material. Both time and scale dependence during pore fluid diffusion in saturated sand are captured, eliminating the mesh dependency for finite element implementations. The model is applied to the Gauss points that satisfy the bifurcation criterion. The proposed method is calibrated to recreate the undrained macroscopic response bestowed by an extra‐small mesh. The microscopic behaviours inside and outside shear band predicted by this model are qualitatively in good agreement with individual material point behaviours inside and outside the shear band in the extra‐small mesh. Depending on the loading rate and the shear band thickness, the response inside the band can be fully or partially drained, which governs the ultimate global strength. The calibrated model is exploited to simulate an upscaled biaxial compression test with semipermeable boundaries.

中文翻译：

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二维模型的饱和膨胀硬化材料局部变形建模

膨胀砂的不排水变形会产生负的超孔隙压力。它增强了强度，这称为膨胀硬化。这种增加的吸力不是永久的。晶粒度的异质性触发了局部化，导致局部体积变化。负水力梯度将流体驱动到扩张剪切区。它会使土壤疏松并降低剪切强度。重要的是要了解这种内部排水的机制，并对其进行数值捕获。本文的目的是在局部或局部排水的剪切带存在的情况下，为饱和致密砂土的不排水变形建立宏观的本构关系。对于带和完整材料会生成单独的本构关系。捕获了饱和砂中孔隙流体扩散过程中的时间和尺度相关性，从而消除了有限元实现中的网格相关性。该模型应用于满足分叉标准的高斯点。所提出的方法经过校准，可以重新创建由超小网格赋予的不排水的宏观响应。该模型预测的内部和外部剪切带的微观行为在质量上与超小网格中剪切带内部和外部的单个材料点行为良好吻合。根据加载速率和剪切带厚度，带内部的响应可以全部或部分耗尽，从而决定了最终的整体强度。该校准模型被用来模拟具有半渗透边界的高档双轴压缩试验。