​The goal of this paper is to evaluate the use of electromagnetic and mechanical waves to monitor the evolution of high-porosity granular salt during constrained loading, thermal changes, and moisture changes. Experimental results show that P and S wave velocities are better correlated with cumulative strain than with stress; the opposite is true for amplitude. This behavior can be explained at the micro-level using Hertzian and frictional contact laws. The complex dielectric permittivity is primarily sensitive to changes in moisture content; load and compaction-creep do not alter the prevailing polarization mechanisms. Other observations relate to creep rates, residual effects of temperature cycles and transient changes in wave velocity immediately after flooding. The magnitude of changes in the measured parameters support the monitoring of granular salt backfill with wave-based techniques.