Evolution of dilation with time based on the molecular microkinetics of red-bed argillaceous sandstone in Hubei Province, China

Red-bed argillaceous sandstone is a typical soft rock with swelling characteristics and is prone to cause problems in engineering geology such as dilation deformation when used in high-speed railway subgrades or uneven settlement when used in foundations. This potential impact emphasizes the importance of understanding the long-term dilation and contraction of red-bed soft rocks. To thoroughly study the dilation properties of red-bed soft rock, the evolution of red-bed argillaceous sandstone dilation over time was characterized through a series of tests. The red-bed argillaceous sandstone dilation has a conspicuous time effect, and the dilatability shows an increasing reverse sigmoidal curve with increasing time. The dilation deformation gradually increases with increasing dry–wet cycle number until the shrinkage deformation offsets the dilation deformation, finally reaching a balance between dilation and shrinkage. Here, the microscopic mechanism of red-bed argillaceous sandstone dilation was revealed by qualitative analysis of microscopic unit particles and quantitative analysis of microscopic pores. A logistic evolution model was established based on molecular microkinetics, with the inflection point (t0) and slope (p) of the dilation curve. The mathematical significance and applicability of the logistic model were verified by model comparison, model application and parametric analysis. The dilation scale and velocity were determined to be restrained by the axial load, and the decrease in the gap between dilation-time curves indicated that the inhibitory effect of the axial load on the expansion potential was nonlinear; with the same axial load increment, this effect weakened with increasing load. Finally, a three-dimensional dilation constitutive model considering the microkinetic time model was proposed to amend the traditional one-dimensional dilation model, and the practicality of this three-dimensional model was evaluated against measured data. The results provide a theoretical reference for solving argillaceous sandstone swelling problems in water-rich red-bed rock and determining the long-term deformation mechanism of high-speed railway subgrades. •Logistic distribution curve describes the evolution of the dilation with time.•Face-face connections have the most favourable spatial arrangement for expansion.•Dilation scale and velocity were determined to be restrained by axial loading.•A three-dimensional dilation constitutive model considering tim