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proof of healing in salt rocks. It has to be mentioned that further experiments are necessary to establish
the dependency between the mechanical and hydraulic properties of the interfaces between the
salt blocks among self and between the blocks and the host rock (rock salt).
Figure 3. Shear strength characteristics of lab-dry and moistened brick-brick and brick-rock salt
contacts. Healing effects, as indicated by development of cohesion, are promoted by the presence of
moisture and increase systematically with stationary ageing over 16, 70 and 94 hours at fixed normal
stress (multiple step tests at constant normal stress). – modified after [3].
3.2 Review of appropriate material laws for modelling granular salt compaction
Four published constitutive models (ITASCA, HEIN, ZANG and SPIERS, for details see [1]) describing
crushed salt behaviour have been evaluated and adapted to recalculate the measured longterm
hydrostatic creep behaviour to remaining porosities in the order of some few percent, i.e. in
the order of natural salt.
Actually the ZHANG model [5] seems to be the most suitable constitutive law to describe the compaction
behaviour of the pre-compacted crushed-salt bricks (compare modeling curves for wet salt
in Fig. 1). However an implementation in commercial available codes is necessary allowing prognosis
calculations for real underground situations. Nevertheless, the potential of the SPIERS mechanism
based pressure solution-model (e.g. [6]) for future modeling is obvious but requires more experimental
work.
The new MINKLEY-shear model for contact interfaces, which implies the displacement-dependent
and the velocity-dependent strength softening is a suitable constitutive law to describe the contact
between pre-compacted crushed salt bricks and to the host rock. This shear model is already implemented
in a commercial code allowing prognosis calculation for real underground situations.
The remaining task is to study and to describe the coupled HM-behaviour of such contact interfaces
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