Abstract: In this paper, a large number of one-dimensional tests, including constant water content compression and soaking under constant stress, are conducted. The microstructure evolution and deformation mechanism of the compacted loess under loading and wetting conditions are investigated with mercury intrusion porosimetry (MIP) and scanning electron microscope (SEM) analysis. Experimental results show that, as the saturation of compacted loess increases at a constant moisture content, it will develop into a saturated consolidation process under further compression. At the microscopic level, the compression of the unsaturated compacted loess results from the collapse reduction of its macrospores, while the distribution of microspores is unaffected in compression. During increasing wetting under the constant vertical stress, the wetting deformation of compacted loess shows a trend of increasing and then decreasing with the increase of vertical stress, and the maximum wetting strain occurs near the compaction stress. Under wetting conditions, the bonds between particles and aggregations are weakened, and the particles and agglomerates collapse and slip, resulting in the reduction of macrospores and the increase of microspores. Also, the soil structure tends to be more uniform and stable after wetting. The creep of compacted loess is caused by the further slippage of particles under constant load and further compression of macrospores. In addition, the settlement law of compacted loess fill is summarized from the construction and post-construction period according to testing results.

Key words: compacted loess, one-dimensional compression and wetting test, microstructure analysis, pore size distribution, deformation upon wetting