It is important to clarify the mechanisms of molten-fuel-pool sloshing behavior that might be encounteredduring a core disruptive accident of sodium-cooled fast reactors. In this study, motivated byacquiring some evidence for understanding the characteristics of this behavior at more realistic conditions,a number of experiments are newly performed by injecting nitrogen gas into a water pool with theaccumulation of solid particles. To achieve comprehensive understanding, various parameters includingparticle bed height, particle size, density, shape, gas pressure along with the gas-injection duration, wereemployed. It is found that due to the different interaction mechanisms between solid particles and thegas bubble injected, three kinds of regimes, termed respectively as the bubble-impulsion dominantregime, the transitional regime and the bed-inertia dominant regime, could be identified. The performedanalyses also suggest that under present conditions, all our experimental parameters employed can havenoticeable impact on the regime transition and resultant sloshing intensity (e.g. maximum elevation ofwater level at pool peripheries). Knowledge and fundamental data from this work will be used for thefuture verifications of fast reactor severe accident codes in China