Pile foundations frequently endure dynamic loads, necessitating an in-depth examination of the cyclic shear properties at the pile–soil interface. This study involved a series of cyclic direct shear (CDS) tests conducted on sand and concrete with irregular surface, utilizing varying displacement amplitudes (1, 3, 6, and 10 mm) and joint roughness coefficients (0.4, 5.8, 9.5, 12.8, and 16.7). Discrete Element Method (DEM) models, informed by experimental data, facilitated mesoscopic mechanical response analyses. Findings indicate that the sand–concrete interface undergoes softening, with hysteresis loops' morphology dependent largely on displacement amplitude. A maximum ultimate shear stress corresponds to a specific critical surface roughness, while the initial tangent modulus escalates with increased concrete roughness. Volume variations of the specimen inversely correlate with displacement amplitude and directly with surface roughness. As displacement amplitude expands, there is a reduction in the maximum shear stiffness and an elevation in the maximum damping ratio. Empirical formulas for the surface roughness and normalized shear stiffness were proposed. Larger displacement amplitudes result in more substantial shear bands and heightened energy dissipation, yet the incremental energy ratio remains largely unaffected. Predominant energy dissipation mechanisms include both slip and rolling slip, with the former surpassing the latter in energy dissipation capacity. The anisotropy directions of contact normal, normal contact forces, and tangential contact forces consistently fluctuate with shear direction alterations.

中文翻译：

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分析砂-粗糙混凝土界面处的循环剪切行为：不同位移幅度的实验和 DEM 研究

桩基经常承受动荷载，因此需要深入检查桩土界面的循环剪切特性。本研究涉及在具有不规则表面的沙子和混凝土上进行一系列循环直剪 (CDS) 试验，利用不同的位移幅度（1、3、6 和 10 毫米）和接缝粗糙度系数（0.4、5.8、9.5、12.8、和16.7）。离散元法 (DEM) 模型根据实验数据，促进了细观机械响应分析。研究结果表明，砂-混凝土界面发生软化，磁滞回线的形态很大程度上取决于位移幅度。最大极限剪切应力对应于特定的临界表面粗糙度，而初始切线模量随着混凝土粗糙度的增加而增大。样本的体积变化与位移幅度成反比，与表面粗糙度成正比。随着位移幅度扩大，最大剪切刚度降低，最大阻尼比升高。提出了表面粗糙度和归一化剪切刚度的经验公式。较大的位移幅度会导致更大的剪切带和更高的能量耗散，但增量能量比基本上不受影响。主要耗能机制包括滑移和滚动滑移，前者的耗能能力优于后者。接触法向、法向接触力和切向接触力的各向异性方向始终随着剪切方向的变化而波动。