ABSTRACT
Based on these projects a third joint project funded by the German Federal Ministry of Economic Affairs and Energy started in 2010. A main task of the third project is to compare the capabilities of different constitutive models used by the individual project partners to image the stress strain behaviour of underground structures in the vicinity of repositories for high level radioactive wastes taking into account damage free as well as damage induced creep and healing behaviour respectively damage reduction behaviour of rock salt (Hampel et. al., 2015). To do the bench mark tests first of all a heating test conducted in the eighties by the Netherlands Energy Research Foundation ECN at Asse salt mine was selected. A second example is given by the so called “Dammjoch” which is a backfilled 85 years old drift at Asse mine characterized by damage reduction processes induced in the drift contour by long term convergence. At least a back-calculation of open drift situations in the Waste Isolation Pilot Plant (“Room B” and “Room D” of WIPP) including an in-situ heater
1 INTRODUCTION
For several decades, the geomechanical behavior of rock salt has been investigated resulting in the development of powerful constitutive models. Between 2004 and 2010, within two joint projects funded by the German Federal Ministry of Education and Research, several project partners documented their constitutive models for rock salt and compared their ability in numerical simulations. Both joint projects were focused on the investigation of damage-free and damage-induced creep behavior of rock salt. For this purpose, salt typespecific laboratory tests on rock salt from Asse site have been performed and based on these results each partner has determined model-specific parameter values. In back-calculations of laboratory tests and selected 2-D and 3-D real underground structures the partners checked the ability of their models and compared their modeling results among each other as well as a present in-situ measurement data. The contents of both research projects were presented at SaltMech6 conference in Hannover in 2007 (Schulze et al., 2007, Hou et al., 2007, Hampel
experiment, which was conducted in the 80’s by Sandia (Munson et al. 1988, 1990) was selected. The WIPP site as a bedded salt repository is characterized of mainly argillaceous salt with a pure rock salt (clean salt) layer above the disposal area. To realize numerical back-calculations of the local rock salts with damage free as well as damage induced stress-strain behavior at different temperatures new advanced triaxial laboratory tests are required to determine the mechanical behavior of these WIPP site facies. The paper concerns information about the testing techniques and test evaluations used within the laboratory program as well as the test results regarding the aforesaid material properties. The planned laboratory program has taken into account the demands, given by different constitutive models to estimate a full set of parameters in each case. To enable each individual project partner to determine model parameter belonging to his constitutive model, digital tables of measurement results concerning time, strain, confining pressure, axial stress, dilatancy and ultrasonic wave velocity have been prepared for each single test. To share the total work of laboratory investigations needed within the joint project laboratory tests on clean salt from WIPP site were mainly performed by IfG whereas laboratory tests on argillaceous salt from WIPP site have mainly conducted by Clausthal University of Technology. The core material used for both laboratory programs has been excavated by Sandia National Laboratories. In total 5.5 tons of 11” diameter cores were drilled, packed and shipped to IfG in Germany. From these large cores IfG has prepared samples by coring perpendicular to the axis of the large cores, that is to say the sample axis in each case are in direction of the depth at WIPP site. The following paper exclusively describes the laboratory investigations done on argillaceous salt from WIPP site. Laboratory investigations done on clean salt from WIPP are presented in a paper given by IfG.
