Abstract: The microstructure changes of Q2 loess in Pucheng power plant, Shaanxi province before and after wetting are studied by using Quanta ESEM (environment scanning electron microscope). A lot of microstructure pictures are obtained. The microstructure qualitative analysis results of Q2 loess before and after wetting with different pressures show that the intra-particle pores are more sensible to pressure and water than inter-particle pores. The maximum pressure of collapsibility of Q2 loess is more than 200 kPa. The area proportion, the roundness, the orientation and the distribution fractal dimension of pore, the gray entropy, the Euler value decrease with increase of pressure and wetting; however, the area proportion, the roundness, the orientation and the distribution fractal dimension of particle increase with pressure and wetting. The quantities of pores with diameter greater than 20 ?m during wetting; while the quantities of pores with diameter less than 20 ?m the pore content increases during wetting. Most pores change during wetting; the large pores turn into medium and small pores; the medium and small pores turn into smaller pores. The peculiar collapsibility of Q2 loess can be explained well by the microstructure changes of Q2 loess before and after wetting with different pressures. The microstructure qualitative analysis provides a new method to research the mechanisms of collapsibility of loess.

Key words: Q2 loess, wetting, microstructure, collapsibility