Abstract Rock samples obtained from excavation and fault damage zones are friable, and it is challenging to obtain cylindrical specimens from such rocks using coring bits in the lab. On the other hand, preparation of prismatic specimens may be less destructive because it does not exert excessive rotational torque around the sides of the rock as in the preparation of cylindrical specimens. Therefore, prism-shaped specimens could become a more favorable sample geometry when working with highly fragile rock samples. However, prism specimens may experience shape-specific boundary effects during mechanical deformation due to the presences of corners and edges, which might cause differences in the measured rock strength and elastic properties compared to a cylindrical specimen. This study aims to investigate how the corners and edges of prism specimens affect the apparent strength and moduli of samples via comparison of laboratory data and finite element modelling results. We find that the prismatic samples can have higher apparent elastic moduli due to the enhanced confinement at the sample edges, which in turn also increases the measured compressional strengths of prism samples compared to cylindrical samples. Whether this apparent strengthening effect influences laboratory data interpretation will also depend on the degree of sample variability and how well specimen edge boundary conditions are controlled.

中文翻译：

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由边缘限制效应引起的圆柱和棱柱试样之间的表观模量和强度差异

摘要 从开挖和断层损伤区获得的岩石样品易碎，在实验室中使用取芯钻头从此类岩石中获取圆柱形样品具有挑战性。另一方面，棱柱试样的制备可能具有较小的破坏性，因为它不像在圆柱试样的制备中那样在岩石侧面施加过大的旋转扭矩。因此，在处理高度脆弱的岩石样品时，棱柱形样品可以成为更有利的样品几何形状。然而，棱柱试样在机械变形过程中可能会由于角和边缘的存在而经历特定形状的边界效应，这可能会导致与圆柱形试样相比，测得的岩石强度和弹性特性存在差异。本研究旨在通过实验室数据和有限元建模结果的比较，研究棱镜试样的角和边缘如何影响样品的表观强度和模量。我们发现棱柱样品可以具有更高的表观弹性模量，因为样品边缘的约束增强，这反过来也增加了棱柱样品与圆柱样品相比的测量抗压强度。这种明显的强化效果是否会影响实验室数据解释还取决于样品变异的程度以及样品边缘边界条件的控制情况。我们发现棱柱样品可以具有更高的表观弹性模量，因为样品边缘的约束增强，这反过来也增加了棱柱样品与圆柱样品相比的测量抗压强度。这种明显的强化效果是否会影响实验室数据解释还取决于样品变异的程度以及样品边缘边界条件的控制情况。我们发现棱柱样品可以具有更高的表观弹性模量，因为样品边缘的约束增强，与圆柱样品相比，这反过来也增加了棱柱样品的测量抗压强度。这种明显的强化效果是否会影响实验室数据解释还取决于样品变异的程度以及样品边缘边界条件的控制情况。