Effects of cyclic loading on mechanical properties of Maha Sarakham salt

A series of laboratory testing has been performed to assess the effects of cyclic loading on compressive strength, elasticity and time-dependency of the Maha Sarakham rock salt. Results from the cyclic loading tests indicate that the salt compressive strength decreases with increasing number of loading cycles, which can be best represented by a power equation. The salt elastic modulus decreases slightly during the first few cycles, and tends to remain constant until failure. It seems to be independent of the maximum loads within the range used here. Axial strain-time curves compiled from loci of the maximum load of each cycle apparently show a time-dependent behavior similar to that of creep tests under static loading. In the steady-state creep phase, the visco-plastic coefficients calculated from the cyclic loading test are about an order of magnitude lower than those under static loading. The salt visco-plasticity also decreases with increasing loading frequency. Surface subsidence and cavern closure simulated using parameters calibrated from cyclic loading test results are about 40% greater than those from the static loading results. This suggests that application of the property parameters obtained from the conventional static loading creep test to assess the long-term stability of storage caverns in salt with internal pressure fluctuation may not be conservative. (C) 2010 Elsevier B.V. All rights reserved.