Temperature effect on the rock salt instant strength characteristics

Abstract

The mechanical behavior of rock salt has been studied for many decades. Early engineering studies were driven largely by the need to design safe salt mines. In recent times more of the study is concerned to understand the long term behavior of the rock salt to develop and assess the safety of rock salt deposits for the storage of radio active waste. The physical and mechanical characteristics of salt are evidenced in its compact texture, low porosity, low permeability and strong rheological properties (creep behavior). These properties are however necessary for stability analysis and the design of engineering structures in salt mines. Long term effect of the temperature on rock salt mechanical behavior has been documented by various researchers. Temperature also has pronounced effect on short term behavior like instant strength of the rock salt. Generally the trend is that as the temperature increases the instant strength decreases. For the stability of structures like solution-mined caverns, dry salt mines, storage and disposal caverns and boreholes used in the exploration and production of oil and gas comprehensive study of the instant strength of the rock salt is also vital. The objective of this research was to study the temperature effect on the instant strength of the rock salt obtained from Polkowice - Sieroszowice mine in the Lower Selicia. After laboratory tests using uniaxial compressive strength test method, it was observed that the at the given range of temperature applied in the test (10 degree C to 80 degree C) the rock salt instant strength does not show any correlation with the temperature. In other words the instant strength of the rock does not decrease as temperature increase. This kind of unanticipated behavior towards the temperature in terms of strength which is rare for the rock salt could be due to the reason that the range of temperature used in the test was not sufficient for the rock salt to show any alteration in its strength value. Since there was no significant effect of given temperature range on the strength values of the rock salt, classical failure criterion like Mohr-Coulomb criterion was considered as the suitable criterion to justify the strength changes on the rock salt samples. On the other hand density emerges out as a crucial factor that influences the instant strength of the rock salt. Higher uniaxial compressive strength values can be observed for the samples having higher density. This research work is useful to understand the mechanical behavior of the rock salt which behaves in a complex manner when there are lots of factors involved like geology, temperature, density, loading history, maturity of the crystals etc. are involved. It is therefore deemed necessary that more through studying and testing is required.