Abstract: Silicification is one of the chemical methods of collapsible loess treatments. Sodium silicate is modified by potassium silicate for better reinforced effect. The mercury intrusion porosimetry (MIP), scanning electron microscope and energy dispersive spectrometer tests (SEM-EDS) are performed on the loess specimens reinforced by compound modified sodium silicate. The microscopic characteristics, such as the entrance pore size distributions, particles' morphology and chemical composition, are carried out. Meanwhile, the relationship between microstructure, chemical composition and macroscopic mechanical behavior is also discussed. Based on the results of MIP, similar entrance pore size distributions, the dual-porosity structure, were found in both modified and unmodified reinforced loess specimens. And the entrance pore size distribution ranges from 0.06 to 8 ?m. According to the decreasing size, the pores can be labeled as large, medium, small and micro-pore, among which the three critical values are 8, 2 and 0.06 ?m, respectively. Moreover, gel-filled effect can be observed if reinforced effect is not significant. The results of SEM-EDS tests show that loess specimens retain granular, trellis pores, contact-cement microstructure after modification. The surface of loess particles became rough and floc was adsorbed after adding potassium silicate material. The EDS data represents that the K element content increases with the increasing of incorporation of potassium silicate. And the unconfined strength of specimens is positively correlated with the percentage of K element. It is also shown that connection strength of soil particles and the structure morphology are the main factors of the macroscopic mechanical properties of loess. The mechanism of loess reinforcement by compound modified sodium silicate is reinforcement of the bond strength of cement in microstructure and formation of three-dimensional networks of frame.

Key words: loess, sodium silicate, potassium silicate, mercury intrusion porosimetry, SEM-EDS test, cementation