Abstract: Clay compacted at the dry side of optimal moisture content generally has a distinct double pore structure, inter-aggregate pore (also called macroscopic pore) and the intra-aggregate pore (also called microscopic pore). The significant difference of their influences on mechanical responses and water retention behaviors of soils leads to the discrepancy on the evolution rules of these two types of pores. The pore size distribution function of unsaturated soil with double pore structure is the bimodal pore size distribution form, which can be obtained by superposing the unimodal pore size distribution curves of macroscopic pores and microscopic pore. The evolution parameters of translation degree, scaling degree and dispersion degree, are adopted to describe the pore evolution rule of soils with double pore structure. Based on establishing the relationship between the evolution parameter and the porosity during mechanical and hydraulic loading and unloading, a model of the microstructural evolution of soils with dual-pore structure suitable for describing unsaturated compacted soils under variable suction was proposed. Based on the results of mercury intrusion tests on Guilin red clay and the test data of Minia Lubois expansive soil in the literature, the established model parameters were calibrated. The applicability and prediction accuracy of the model was verified by comparing the simulation results with test results.

Key words: unsaturated soil, double-pore structure, bimodal pore size distribution function, pore size evolution;