Penetration of open- and closed-ended model piles into intact chalk, a soft calcareous rock, was investigated using microfocus X-ray computed tomography (XCT). Three-dimensional images of the specimens showed that the piles crushed and densified the chalk in their path, creating a crushed chalk annulus around the shaft, a region of compressed destructured chalk below the tip, and fractures across cemented regions of the specimen. Laser-diffraction particle-size analyses of the crushed chalk annulus after exhumation showed limited difference with laboratory-remoulded chalk, which suggested thorough de-cementation. Installation stresses and XCT-derived densities were paired using a simplified cylindrical cavity expansion solution to estimate effective radial stress–void ratio states at the pile tip during penetration. More complex numerical solutions could not be applied using the available data. This approach posed significant problems, as it could not suitably incorporate hardening and non-linear stiffness behaviours of chalk during pile penetration, nor account for the creation of discontinuities. However, effective radial stress–void ratio estimates were found to converge with the reconstituted critical state line of the material at high stresses and low void ratios. This partially supported the use of a critical state framework to characterise pile penetration in chalk, as proposed in recent literature.

中文翻译：

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使用 X 射线计算机断层扫描法研究钙质软岩中的桩穿透

使用微焦点 X 射线计算机断层扫描 (XCT) 研究了开放式和封闭式模型桩对完整白垩（一种软钙质岩石）的渗透。样本的 3D 图像显示，桩在其路径中压碎并致密白垩，在轴周围形成压碎的白垩环，尖端下方的压缩破坏白垩区域，并在试样的胶结区域断裂。折返后粉碎的白垩环的激光衍射粒度分析显示与实验室改造的白垩的差异有限，这表明彻底脱胶。安装应力和 XCT 导出的密度使用简化的圆柱形扩腔解决方案配对，以估计穿透期间桩尖的有效径向应力-空隙比状态。使用可用数据无法应用更复杂的数值解。这种方法带来了重大问题，因为它不能适当地结合桩穿透过程中白垩的硬化和非线性刚度行为，也不能解释不连续性的产生。然而，发现有效的径向应力-空隙率估计值在高应力和低空隙率下与材料的重构临界状态线收敛。这部分支持了使用临界状态框架来表征粉笔中的桩穿透，正如最近文献中提出的那样。然而，发现有效的径向应力-空隙率估计值在高应力和低空隙率下与材料的重构临界状态线收敛。这部分支持了使用临界状态框架来表征粉笔中的桩穿透，正如最近文献中提出的那样。然而，发现有效的径向应力-空隙率估计值在高应力和低空隙率下与材料的重构临界状态线收敛。这部分支持了使用临界状态框架来表征粉笔中的桩穿透，正如最近文献中提出的那样。