The in situ state of rock mass stresses is a key design parameter, e.g., for deep engineered geothermal systems. However, knowledge of the stress state at great depths is sparse mostly because of the lack of possible in situ tests in deep boreholes. Among different options, core-based in situ stress estimation may provide valuable stress information though core-based techniques have not yet become a standard. In this study we focus on the Diametrical Core Deformation Analysis (DCDA) technique using monzogranitic to monzonitic rock drill cores from 4.9 km depth of the Basel-1 borehole in Switzerland. With DCDA the maximum and minimum horizontal stress (S_Hmax and S_hmin) directions, and the horizontal differential stress magnitudes (∆S) can be estimated from rock cores extracted from vertical boreholes. Our study has three goals: first, to assess photogrammetric core scanning to conduct DCDA; second, to compare DCDA results with borehole breakout and stress-induced core discing fracture (CDF) data sets; and third, to investigate the impact of rock elastic anisotropy on ∆S. Our study reveals that photogrammetric scanning can be used to extract reliable core diametrical data and CDF traces. Locally aligned core pieces showed similar S_Hmax orientations, conform to borehole breakout results. However, the variability of core diametrical differences was large for the Basel-1 core pieces, which leads to a large spread of ∆S. Finally, we demonstrate that core elastic anisotropy must be considered, requiring robust estimates of rock elastic moduli, to receive valuable stress information from DCDA analyses.

岩体应力的原位状态是一个关键的设计参数，例如，对于深部工程地热系统。然而，对大深度应力状态的了解很少，主要是因为在深钻孔中缺乏可能的现场测试。在不同的选项中，虽然基于岩心的技术尚未成为标准，但基于岩心的原位应力估计可能会提供有价值的应力信息。在这项研究中，我们重点研究了直径岩心变形分析 (DCDA) 技术，该技术使用来自瑞士 Basel-1 钻孔 4.9 公里深度的二长花岗岩至二长岩钻孔岩心。DCDA 的最大和最小水平应力（S _Hmax和S _hmin）方向，以及水平差异应力大小（∆ S) 可以根据从垂直钻孔中提取的岩心进行估算。我们的研究有三个目标：第一，评估摄影测量核心扫描以进行 DCDA；其次，将 DCDA 结果与钻孔崩裂和应力诱导的岩心钻削裂缝 (CDF) 数据集进行比较；第三，研究岩石弹性各向异性对 ∆ S 的影响。我们的研究表明，摄影测量扫描可用于提取可靠的岩心直径数据和 CDF 轨迹。局部对齐的芯片显示出类似的S _Hmax方向，符合钻孔突破结果。然而，Basel-1 芯块的芯直径差异的可变性很大，这导致 ∆S 的大范围传播。 最后，我们证明必须考虑岩心弹性各向异性，需要对岩石弹性模量进行稳健估计，才能从 DCDA 分析中获得有价值的应力信息。