Abstract: One-dimensional swelling tests under different load conditions were conducted to obtain the evolution of Nanyang expansive soil’s microstructure. Samples with initial state and samples swelling under different conditions were freezing-dried to get prepared for Scanning Electron Microscope (SEM) tests and Mercury Intrusion Porosimetry (MIP) test. Then the modification in microstructures and pore size distribution were analyzed. SEM tests show that soil-particle arrangement has no obvious directionality. Samples with initial compacted state and swelling under constant volume are in turbulent flow structures, while samples swelling under 0 or 50 kPa surcharge are of granular structures after reaching steady state. MIP test shows that the pore size distribution curves of samples under different swelling conditions are of three peaks. Pores in soils can be classified into macro-pore, fine-pore, micro-pore and ultra-micro-pore. Compared with initial states, fine-pores in samples swelling under constant volume are compressed into micro-pore. The volumes of all kinds of pores in samples swelling under 0 or 50 kPa surcharge loads all increase as the surcharge loads are larger than the expansive force. In this situation, soil particles can push each other away.

Key words: weak expansive soil, microstructure, pore size distribution, one-dimensional swelling, MIP, SEM