Extension of biaxial highpressure test system

本装置是将现有双轴试验系统进一步发展和改进为真三轴压缩载荷试验系统。按照双轴试验系统的概念，三轴试验系统中的棱柱形试件将通过6块钢板加载。众所周知，中间主应力对岩石的变形和强度特性有决定性的影响。地壳内的主应力状态和空腔及地下构造影响范围内的次应力状态均具有较强的各向异性。因此，当研究具有大各向异性特征的情况和条件时，在实验室规模上对这些加载边界条件的实验再现是至关重要的。由于在传统的三轴试验（卡门型）中，两个主法向应力总是相同的，因此不能用这种技术来研究平均主法向应力的影响。真正的三轴压缩载荷测试装置目前在弗莱堡工业大学或与之有研究合作的机构都没有。因此，我们的工作组无法获得这样的测试技术，也无法处理与之相关的高度热门的研究课题。真三轴测试装置结构类型选择的核心方面如下：•从100到300 mm边缘长度的棱柱形试样尺寸的灵活选择•实现大压应力（根据试样尺寸可达200 MPa）•所有轴上的动态加载可能性(例如循环加载，地震信号或单一冲击)继续进行具有良好监测可能性的双轴测试；直接通过压力板耦合变形测量传感器和压电陶瓷传感器；在测试样品中实现均匀应力和变形场；该设备将用于以下主题的研究项目应用于结晶岩石断裂时的各向异性强度行为；花岗岩深部地热井的稳定性；三轴载荷下断裂岩石的行为；山脉形成过程/用岩石和等效材料选择造山过程的实验模拟

The device applied for is a further development and improvement of an existing biaxial test system into a test system for true triaxial compressive loading. Following the concept of the biaxial test system, prismatic specimens in the triaxial test system will loaded through six steel plates. It is well known that the intermediate principal stress has a decisive influence on the deformation and strength behaviour of rocks. Both, primary stress states in the earth's crust and secondary stress states in the sphere of influence of cavities and underground structures are generally strongly anisotropic. Experimental reproduction of these loading boundary conditions on a laboratory scale is therefore of central importance when situations and conditions characterized by great anisotropy are investigated. Since in conventional triaxial tests (Karman-type) two principal normal stresses are always the same, the influence of the mean principal normal stress cannot be investigated with this technique.A testing device for true triaxial compressive loads is currently not available either at the TU Bergakademie Freiberg or at institutions with which research cooperations exist. Therefore, our working group has no access to such testing technology and cannot deal with highly topical research topics associated with it. Central aspects in the choice of the type of construction of the true triaxial testing device were the following: Flexible choice of size of prismatic specimens from 100 to 300 mm edge length Realization of large compressive stresses (up to 200 MPa depending on specimen size) Possibility of dynamic loading in all axes (e.g. cyclic loading, earthquake signal or singular impact) Continued possibility of biaxial testing with good monitoring possibilities Coupling of sensors for deformation measurement and piezoceramic sensors directly via the pressure plates Realization of a homogeneous stress and deformation field in the test specimenThe equipment will be used in research projects on the following topics: Development and testing of an extended hydro-mechanical-coupled Hoek-Brown failure criterion for the assessment of anisotropic strength behaviour when applied to fracture of crystalline rocks Stability of deep geothermal wells in granite Behaviour of fractured rock under triaxial loading Mountain formation processes / Experimental modeling of selected orogenesis processes with rocks and equivalent materials