Abstract: Gobi is a common geological formation in Northwest China. The gobi gravel soil is made up of the coarse-grained soil, the fine-grained soil, and the bond particles among them. Gobi gravel soil contains soluble salts and exhibits salt cementation, which makes it different from other soil-rock mixtures. In this study, the pH values and the soluble concentrations are tested on gobi gravel soil obtained from Xinjiang Autonomous Region and Gansu Province. The mechanism and the type of salt cementation are analyzed. The microstructure, mineral composition, and bond character of structural soil particles were examined by the techniques of X-ray, SEM, and moss-Bauer spectroscopy to investigate the physicochemical mechanism of bond forces. According to the results on the mineral composition and the microstructure, the possible chemical bond types and the physicochemical mechanism of bond forces were suggested. Finally, the mechanical model and the corresponding formulae of the relationship between the shear parameter and the cementation were established, in which the content and distribution of the cementing agent was suggested as the variables. The cohesion values were calculated and compared to the in-situ shearing test results. The results show that the essence of chemical bond is the formation of the ionic bond by the non-metal atoms in the minerals or CaCO3 (for example, by the oxygen atom). The magnitude of this chemical bond force is determined by the ionic bonds. In addition, the contribution of the salt cementation must be taken into consideration in the determination of the shearing strength for gobi gravel soil.

Key words: gobi gravel soil, bond force, microstructure, strength parameters