Speakers
Description
Large scale tests on cylindrical specimen are well established in major rock engineering projects in Germany. Suggested methods of ISRM and DGGT describe the standard procedures. The paper reviews two case studies of LST where testing procedures exceeded the given standards:
• for the 1060 MW Goldisthal Pumped Storage Project prismatic samples were tested under true triaxial loading conditions.
• for the foundation of the ca. 100m high Leibis-Lichte concrete gravity dam, the anisotropy of the schistous rock mass was investigated
PSP Goldisthal in the Thuringian Forrest, developed by VEAG and now owned and operated by Vattenfall, was built from 1997 to 2003. The true triaxial LSTs on the prismatic slate/quartzite rock samples (62 x 62 x 120 cm³) simulated the potential failure mode in the long side walls of the powerhouse cavern (width 25.8 m, height 48.5 m, length 137.4 m) and supported the optimization of the rock support design.
The design of the Leibis-Lichte concrete gravity dam (owned by the Thüringer Fernwasserversorgung and commissioned in 2005) has required the determination of the strength and deformability of the foundation in schistous rock mass. LST on cylindrical and prismatic samples were performed on specimens, which had orientations of the planes of schistosity parallel and normal to the maximum principal stress. Additionally, the strength and deformability of the discontinuities were investigated in direct shear tests. It can be shown, that laboratory tests, combined with the numerical triaxial tests give robust results of the strength and deformation parameters of the rock mass.
The authors are convinced that the above described tests performed in the 1990ies delivered valuable results to the respective owners that supported the definition of reasonable parameters, allowing for optimized designs. The paper intends to promote the use of true triaxial LST in rock for situations where the rock mass shows distinct anisotropy, which may be tested representatively in a LST with triaxial loading conditions and will show examples of recent or ongoing projects where the availability of LST could lead to optimized or safer designs or reduced risk, which would justify more extensive testing programs, including true triaxial LST.