Wetting–Drying–Freezing–Thawing Cycle Effect on the Swelling Pressure of Yanji Mudstone Using Various Determination Methods

Abstract

Swelling rocks and soils can generate significant swell or swelling pressure upon contact with water due to their special mineralogical composition, and thus a reliable determination of their swelling property is essential when evaluating the long-term safety and stability of adjacent geotechnical infrastructure. In this work, the swelling pressures of Yanji mudstone before and after seasonal wetting–drying (WD), freezing–thawing (FT) and wetting–drying–freezing–thawing (WDFT) processes were experimentally determined by zero-swell, load-swell, and swell-consolidation methods. It was found that the seasonal processes significantly reduced the swelling pressures determined by different methods because of the contraction of aggregates and the appearance of large pores and fissures/cracks. Due to the more intensive microstructure change, the WDFT process had a more detrimental influence on the swelling pressure of Yanji mudstone than separate WD or FT cycles. Moreover, a comparison among three determination methods showed that a larger swelling pressure was measured by the swell-consolidation method owing to the greater resistance of the even microstructure after hydration under a low vertical stress and the possible friction with cell wall during consolidation compared with the load-swell and zero-swell methods. With the increase of WDFT cycles, this difference method decreased because the large pores and fissures/cracks could increase the compressibility of swollen specimens in the swell-consolidation tests and accelerate the water infiltration in the zero-swell and load-swell tests.