Swelling–shrinkage mechanisms of diatomaceous soil and its geohazard implication

Current understanding of soil behaviors from classic soil mechanics is constantly challenged by a variety of unusual soils, one of which is diatomaceous soils (DSs). It is well understood that this biological-origin soil has fundamentally different geotechnical features from that of common fine-grained soils because of the presence of diatom fossils. Recently, increasing geohazards and engineering disasters associated with DS swelling–shrinkage are reported but the exact role of diatoms in determining soil swelling–shrinkage, the underlying mechanisms, and the geohazard implications, have not yet been revealed. This study systematically investigates the swelling–shrinkage behavior of natural DS as well as artificial mixture of diatoms and clay minerals (kaolinite and montmorillonite). The swelling–shrinkage behaviors are explained from the perspectives of mineralogy and microstructure as revealed through X-ray diffraction, scanning electronic microscopy, and transmission electron microscopy. Diatoms have a special microstructure with inter-frustule pores, and the intra-skeletal and skeletal pores in DS make the soil characterized by a high void ratio and water content. In addition, the presence of diatoms curbs the swelling–shrinkage of DS but this may be overwhelmed by the high stress generated due to the swelling of montmorillonite. The wetting–drying cycles subjected to DS result in fissure development, a higher level of swelling–shrinkage behavior, and ultimately in related geohazards such as landslides. The distinct swelling–shrinkage behavior of DS makes the previous classification inapplicable; thus, more rational classification methods are adopted. This study enhances the understanding of the swelling–shrinkage behavior of DS and the control of related geohazards. •Swelling-shrinkage of diatomaceous soil is studied and the mechanism is revealed.•Diatom is found to have special microstructure with inter-frustule pores.•Diatom curbs swelling-shrinkage but this cannot hold upon high clay mineral content.•Wetting-drying cycles cause higher shrinkage-swelling potential.•Swelling-shrinkage behavior of the studied soil is classified.