Polyaxial Strength Criteria and the Assessment of the In Situ Stress Magnitudes in the KTB Ultra Deep Borehole

KTB项目位于德国东南部，是前苏联以外世界上最深的科学钻探项目（深9.1公里）。这是威斯康星大学和斯坦福大学之间的一个联合项目，代表了美国和德国合作研究项目的延续，通过实施综合应力测量策略，在很大程度上依赖于对井眼观察到的压缩和拉伸破坏的评估，确定应力大小和方向作为KTB井眼深度的函数。迄今为止，这项工作相当成功，但这项工作的一个重要弱点是缺乏足够的岩石强度数据。该项目的目的是填补这一关键空白，从而大大提高我们在深度限制应力大小的能力。具体来说，研究的主要目的是全面研究KTB超深钻孔岩心样品在各种应力条件下的强度：拉伸，单轴，压缩，三轴压缩，特别是真多轴。全面的多轴抗压强度测试将在一个新设计的单元中进行，该单元将最大限度地减少棱柱状岩石样品表面的摩擦。这些研究结果将用于提高KTB井中最大水平主地应力估计的可靠性。＊＊＊

9418738 Haimson The KTB project, located in southeastern Germany, is the world's deepest scientific drilling project outside the former Soviet Union (TD 9.1km). This is a joint project between the University of Wisconsin and Stanford University and represents a continuation of a cooperative US/German research project to determine stress magnitude and orientation as a function of depth in the KTB borehole through implementation of an integrated stress measurement strategy, relying heavily on evaluation of compressive and tensile failures observed in the borehole. To date, this work has been quite successful but an important weakness in this effort has been the lack of sufficient data on rock strength. The purpose of the this project is to fill this critical gap and thus greatly improve our ability to constrain stress magnitudes at depth. Specifically, the principal objective of the research is to comprehensively investigate the strength of core samples from the KTB ultra-deep borehole under a variety of stress conditions: tensile, uniaxial, compressive, triaxial compressive, and in particular true polyaxial. Comprehensive polyaxial compressive strength tests will be conducted in a newly designed cell that minimizes friction at the faces of prismatic rock specimens. The results of these studies will be used to improve the reliability of estimates of the maximum horizontal principal in situ stress in the KTB hole. ***