Abstract This study aims to investigate the influence of cementation on the stress-strain and strength characteristics of soil during cavity expansion in lightly cemented sand deposit using three-dimensional discrete element simulations. Contact models, simulating the cementation effects of bonded clumps and capturing the interlocking effects between discrete sand particles, are incorporated to mimic the cemented sands with various cement contents. The microscopic parameters are calibrated and validated against existing experimental results. Real scale cylindrical cavity expansion models starting from zero initial cavity radius with different levels of cementation are developed, and each proposed model consists of 150,000 particles with boundary conditions carefully selected to reproduce the realistic scenario. The embedded scripting is utilised to precisely measure both the local and global stress–strain variations, and record and analyse the cementation bond breakage during the cavity expansion process. The results confirm that the cementation enhances the material strength through the increase in cohesion and tensile strength at the contacting interfaces, whereas the friction angle is not altered notably. Hence, the failure envelope of the cemented sand gradually merges with the critical state line due to the cementation degradation, particularly at a high confining pressure. It was found that the failure mode of the lightly cemented sand adopted in this study, was mainly controlled by the shear rather than tensile strength at the contacting interfaces. Referring to the numerical predictions it is evident that the zone with significant cementation degradation due to the cavity expansion extends as far as 4 a f for all cemented specimens ( a f being the final cavity radius). In addition, specimens with higher cement content experience a more pronounced dilation at the internal cavity wall, while an inverse trend is captured at a greater radial distance. Furthermore, the radial displacement induced by the cavity expansion reveals a larger influence zone in specimens with higher cement content. Therefore, the effects of excessive lateral displacement transferred to neighbouring structures during installation of the displacement-based inclusions in lightly cemented sand should be carefully assessed by practicing engineers.

中文翻译：

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考虑胶结退化的轻胶结砂岩空洞膨胀离散元模拟

摘要 本研究旨在利用三维离散元模拟研究轻胶结砂层中空洞膨胀过程中胶结作用对土体应力-应变和强度特性的影响。结合接触模型，模拟粘结团块的胶结效应并捕捉离散砂粒之间的互锁效应，以模拟具有各种水泥含量的胶结砂。微观参数根据现有的实验结果进行校准和验证。开发了从初始空腔半径为零开始并具有不同胶结程度的真实尺度圆柱空腔膨胀模型，每个提议的模型由 150,000 个粒子组成，并具有精心选择的边界条件以重现现实场景。嵌入式脚本用于精确测量局部和全局应力应变变化，并记录和分析腔膨胀过程中的胶结键断裂。结果证实，胶结通过增加接触界面的内聚力和抗拉强度来提高材料强度，而摩擦角没有显着改变。因此，由于胶结退化，特别是在高围压下，胶结砂的破坏包络线逐渐与临界状态线融合。结果表明，本研究采用的轻胶结砂的破坏模式主要受接触界面处的剪切强度而不是抗拉强度控制。参考数值预测，很明显，对于所有胶结试样，由于空腔膨胀而具有显着胶结退化的区域延伸至 4af（af 是最终的空腔半径）。此外，具有较高水泥含量的试样在内腔壁处经历更明显的膨胀，而在更大的径向距离处捕捉到相反的趋势。此外，空腔膨胀引起的径向位移表明，在水泥含量较高的试样中，影响区域更大。因此，在轻胶结砂土中安装位移型夹杂物期间，过度横向位移转移到相邻结构的影响应由执业工程师仔细评估。