Free iron oxides in soils usually have distinct electrochemical properties, relatively high surface energy, a strong ability to adsorb, and provide structural cementation in the soil. Thus, soil properties are influenced by the content, characteristics and occurrence of free iron oxides. This paper reports a study on Zhanjiang clay and Longmen laterite, both of which are rich in free iron oxides, to investigate the occurrence characteristics of free iron oxides in soils. Dithionite-citrate-bicarbonate solution was adopted to remove free iron oxides from the soils, and qualitative filter paper was used to extract particles with size d \ 25 lm. X-ray diffraction, scanning electron microscopy, and energy dispersive spectrometry were used to analyze alterations in the physical and chemical properties, mineral composition, and microstructure caused by the removal of free iron oxides. The results obtained in this study show that free iron oxides act as a bridge in Zhanjiang clay and mostly in the form of cladding in Longmen laterite. Both forms enhance the cementation and structural strength of the soils and weaken the swelling-shrinkage capacity. The findings of this paper will contribute to a deeper understanding of the formation and failure of soils.
Fully grouted rock bolts are widely used in civil engineering and mining engineering, playing a significant role in keeping the stability and safety of excavations. In this paper, the load transfer mechanism of fully grouted rock bolts was studied with an analytical model. A trilinear model was used to depict the bond-slip behaviour of the bolt/grout interface. The displacement of the confining medium was involved in this analytical model. Then, the shear stress propagation along the bolt/grout interface was analysed in the elastic, elastic-softening, elastic-softening-debonding, softening-debonding, and debonding stages. Experimental pull-out tests were used to validate this analytical model. There was a good correlation between experimental and analytical results. A parametric study was conducted to evaluate the influence of Young’s modulus of the confining medium, the shear strength of the bolt/grout interface, and the residual shear strength of the bolt/grout interface on the load transfer performance of rock bolts. The results show that increasing Young’s modulus of the confining medium was beneficial for improving the load transfer performance of rock bolts. However, once Young’s modulus of the confining medium was beyond a critical limit, it had marginal effect on the peak load of rock bolts. Furthermore, increasing the shear strength of the bolt/grout interface and the residual shear strength of the bolt/grout interface led to rising of the peak load of rock bolts. However, compared with the residual shear strength of the bolt/grout interface, increasing the shear strength of the bolt/grout interface had more apparent effect in improving the peak load of rock bolts.
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