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

小行星9418738 KTB项目位于德国东南部，是世界上除前苏联（TD 9.1公里）外最深的科学钻探项目。 这是威斯康星州大学和斯坦福大学之间的一个联合项目，代表了美国/德国合作研究项目的延续，该项目旨在通过实施综合应力测量策略，在很大程度上依赖于对钻孔中观察到的压缩和拉伸破坏的评估，确定KTB钻孔中作为深度函数的应力大小和方向。 到目前为止，这项工作已经相当成功，但在这项工作中的一个重要弱点是缺乏足够的数据岩石强度。 本项目的目的是填补这一关键空白，从而大大提高我们约束深度应力大小的能力。 具体而言，研究的主要目标是全面调查各种应力条件下的KTB超深钻孔岩心样品的强度：拉伸，单轴，压缩，三轴压缩，特别是真正的多轴。 综合多轴抗压强度测试将在一个新设计的单元中进行，该单元可最大限度地减少棱柱形岩石试样表面的摩擦。 这些研究的结果将用于提高KTB孔中最大水平主原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. ***